Casa del Agua and Desert House: Two Residential Demonstration-Research Projects on Water and Energy Efficiency

Table of contents: 
1. Introduction
2. Casa del Agua
3. Desert House
4. Questions and Answers
5. Endnotes
6. List of Figures

An Essay on a presentation made by Richard Brittain to Diwan al-Mimar on May 31, 2001

Prepared by Mohammad al-Asad and Majd Musa in association with Richard Brittain, 2002

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Support for the publication of this essay has been made possible by a grant from the Prince Claus Fund for Culture and Development. Additional support has been provided by Darat al-Funun - The Abdul Hameed Shoman Foundation.



Richard Brittain (1) started his presentation with a comparison of rainfall patterns in the Sonoran Desert region, particularly in Tucson, Arizona, and in Amman. He mentioned that both have similar levels of precipitation, which amount to approximately 300 mm per year. He added, however, that the rainfall pattern in Tucson is bimodal, but is unimodal in Amman. (2) Tucson has a rainy season during the summer and another one during the winter. The situation is different in Amman where rain falls in one season, from November through March.

Brittain added that the total water demand exceeds the total available renewable supply in Tucson. This is the result of a number of factors including low levels of precipitation, rapid population growth, and the high levels of water consumption by the mining industries and agricultural activities in the area. Therefore, the issue of water conservation in the different sectors of water use in Tucson is of great significance. Brittain believes that implementing an efficient use of the limited water resources on a residential scale can play a significant role in reducing the amount of municipal water used in Tucson. In order to motivate people to save water, residential education and demonstration projects are required.

By a residential demonstration project, Brittain refers to a house that would demonstrate to the public and educate it about water conservation. Such a house would be one in which a family would live, while researchers would monitor the house and record data about how much water is being used and what possible savings in water use might be achieved. Through such a research project, researchers would be able experiment with the use of water-saving mechanisms such as using graywater and rainwater for irrigation. The project also would allow the general public as well as water conservation specialists and other concerned parties to visit it, tour its facilities, and examine the ways in which different water conservation technologies are implemented in a real-world setting. Such a project should also incorporate a public information center that would allow visitors to gain in-depth knowledge about the project and the research being conducted through it. This would allow them to implement in their own residences some of the ideas on water conservation being used in the demonstration house.

When Brittain, at the College of Architecture, and his colleagues at the Desert Research Unit in the Office of Arid Lands Studies (OALS) at the University of Arizona considered their first water conserving demonstration house in 1983, they had been engaged for a number of years in research on various aspects of water conservation. Before they undertook their first demonstration house project, they had realized that the only way they could possibly succeed in achieving higher levels of water conservation in a given community was through involving a large segment of the community and gaining its support. Brittain and his colleagues spent a couple of years discussing the idea of a water-conserving demonstration house with individuals and relevant organizations. Participants included Tucson Water, the Pima County Wastewater Management Department, the University of Arizona, the Southern Arizona Home Builders Association, and building suppliers. (3) According to Brittain, it is this wide level of commitment to the idea of demonstration projects that allowed for the success of the two demonstration houses in which he has been involved. These two projects are described below.

Casa Del Agua

In 1983, the City of Tucson carried out a road-widening project in suburban Tucson, and subsequently bought the houses located along this particular road with the intention of demolishing them. Brittain and his colleagues convinced the city authorities that one of the residential properties had the potential of being modified and retrofitted as a demonstration and research site for water conservation practices. The single-family residence was very close to a shopping mall, which meant that many people would go to that area, and the mall visitors could be attracted to visit the house through effective advertising. The house was given the name "Casa del Agua," which is Spanish for "House of Water." It was opened for visitors in September 1985, and operated as a demonstration house until April 1999, when it became Tucson Water's conservation offices.

Casa del Agua (figure 1) is a typical ranch-style house that had lawn all around it and was landscaped with the high-water-use plants typical of the Tucson area. Also, it conformed to the customary practice in Tucson of diverting all the rainwater that falls on a residential property off the site and into the street where it would end up in the municipal storm sewer system. The project team worked on developing Casa del Agua in order to accommodate water conservation and data collection purposes. The design development was implemented through several modifications to the original structure and the landscaping of the plot on which it is located. Consequently, the project team removed the lawn and vegetation in the front yard, except for the large African sumac (Rhus lancea) tree that provided the western side of the house with highly needed shade. Several years later this tree was blown over in a monsoon storm and was replaced with a mesquite. They created a concave front yard area with a berm around its perimeter to retain rainwater on-site rather than have it end up on the street. The team also built a ramada across the front yard with vines planted next to it to provide additional shade. Moreover, they reconfigured the driveway so that it would slope towards the concave front yard and direct the rainwater into the site.

Figure 1: A view of the Casa del Agua demonstration project in Tucson, Arizona.

Figure 1: A view of the Casa del Agua demonstration project in Tucson, Arizona.

Alterations were also applied to the backyard (figure 2). Most of the lawn area was removed and brick paving was installed with a slope that directed rainwater to a very small lawn area surrounding a tree. Low-water-use plants were installed and irrigated through a drip irrigation system. (4) A passive solar greenhouse was built on the south side of the house. This was used to grow certain food crops, and also to provide the house with passive solar heating in the wintertime.

Figure 2: A view of the backyard of Casa del Agua that shows the concrete paving and extended  rooftop.

Figure 2: A view of the backyard of Casa del Agua that shows the concrete paving and extended

The project incorporated a rainwater harvesting system. (5) The project team increased the harvested rainwater catchment area of the project by increasing the roof area, which now occupied 232 square meters. Storm water was conveyed to underground storage tanks by means of rain gutters and downspouts. Prior to entering the tanks, storm water flowed through a filter box, where a simple window screen was used as a filtration device that would stop the leaves and other debris from making their way into the storage tanks.

Inside the house, the concrete floor of the master bathroom was cut open to reach the drainage pipes located underneath the slab. A new set of pipes was installed to allow for the separation of graywater from blackwater. Graywater, which includes sink, bathtub, shower, and washing machine water, was made to flow into a recycling system. Blackwater, which includes toilet and kitchen sink water, was directed to the municipal sewer system. Here, Brittain mentioned that the project team members decided to route the wastewater from the kitchen sink into the municipal sewer system because of the degradable material it contains from food waste and food scraps. Such materials make the wastewater from the sink hazardous and unsuitable for use without additional treatment.

Sources of graywater at Casa del Agua were the washing machine, the bathroom sinks, the showers, and bathtubs. Graywater drawn from these sources flowed by gravity via the modified drain system below the slab to a 208 liter sump tank located below the floor level of the house. The tank had an overflow valve that connected to the municipal sewer, and had a pump inside it that pumped the graywater through the various experimental treatment systems and into the graywater storage tanks. The pump would automatically operate as the container in which it is submersed fills up with water. The pump serves to reduce the level of the water so that it would not overflow onto the rest of the equipment. Brittain noted that in the context of this project the rainwater pump and pressure tank were separated from the graywater pump and pressure tank. Moreover, each of those systems served separate drip irrigation zones.

Brittain added that the calculations made for the volume of the expected harvested rainwater for the project indicated that storage tanks with a total capacity of about 51 cubic meters were needed. The project team decided to harvest at least half of the annual rainfall that fell on the roof surface and direct that into storage tanks so that the harvested water would be used for irrigation up to the next rain season. Consequently, two large tanks were first assigned for the harvested rainwater. However, after the first two years of the project's operation, it was found that the house was located in a "rain shadow" area, and therefore was not getting the expected amount of rainfall, and the rainwater storage tanks were not getting filled. Consequently, one of those tanks was converted for use as a second graywater storage tank so that graywater could be stored during the wintertime when the plants did not need the graywater for irrigation. The graywater, however, would be used during the arid pre-summer peak demand season (April through June).

Brittain described the underground rainwater storage tanks and their installation process (figure 3). He mentioned that the project team realized that it is costly to excavate and install the tanks. The two tanks were well compression tanks with approximately 16-mm steel walls. Tucson Water had retired a number of these tanks because they were no longer suited for pressurized conditions. The project team welded manways onto the tanks, provided them with lockable lids, and provided the necessary piping work including the inlets, overflows, and suction pipes from the pump. The manway provides access to the tank, which is especially needed for maintaining the foot valve, which retains the pump prime.

Figure 3: The installation of the underground rainwater storage tanks at Casa del Agua.

Figure 3: The installation of the underground rainwater storage tanks at Casa del Agua.

Figure 4 shows the area located above the underground rainwater tanks as it appeared after the project was landscaped in 1985. A mesquite tree (Prosopis velutina) was placed in the area over the tanks. Mesquites are known to have tap roots, so this particular tree was meant to grow between the two tanks to encourage its growing roots to go down into the ground. The heaviest watering needs would be for the small turf area that appears in figure 4 and that was provided with a drip irrigation system. The two potted plants that also appear in figure 4 are placed right on the access manways. Those can be removed whenever access to the tanks is needed. The manways also allow for monitoring the content of the tanks by inserting a calibrated dipstick into holes plugged with corks.

Figure 4: The landscaped area above the underground rainwater tanks at Casa del Agua: lawn area, Mesquite tree, and potted plants placed on the tanks' access manways.

Figure 4: The landscaped area above the underground rainwater tanks at Casa del Agua:
lawn area, Mesquite tree, and potted plants placed on the tanks' access manways.

Brittain also emphasized the "passive" approaches to water conservation that had been adopted in the project. In addition to using water from the graywater system and from the rooftop rainfall harvesting system, water also was passively being harvested. This is achieved by making sure that all rainfall coming to the site was kept in the site. This means that the water that is not collected into tanks would be stored in the soil for direct use. Otherwise, the water would escape into the street, where not only would it be lost, but also would contribute to the problems of urban flooding.

Brittain added that numerous experiments were carried out on the treatment of graywater during the thirteen years of Casa del Agua's operation. The goal was to explore practical means for achieving the highest quality of graywater possible in order to satisfy the Arizona Department of Environmental Quality (ADEQ) standards for surface irrigation without having to chlorinate. This also was one of Pima County Wastewaters' objectives for the project. Recycled graywater was basically used to irrigate the plants and lawn through an automated drip irrigation system. In a few cases, particularly when the harvested rainwater was not available, recycled graywater was even applied to the herb and vegetable gardens.

The harvested rainwater was primarily used for the evaporative cooling system from 1987 to 1991. It also was used as a supplementary irrigation water supply source, particularly for watering vegetables and herbs grown in the landscape or in the greenhouse. Brittain showed an interesting example in which PVC pipes were drilled with holes, hung from the rainwater catchment area, and planted with lettuces that grew out of the holes in the pipes. The plants in the pipes were irrigated with harvested rainwater by means of a drip irrigation system. It was only an experiment, but it shows how creative ideas can come out of the limited available resources. When one does not have much ground area or much water, one can just grow the food from a "hanging garden" and water it with a drip irrigation system (figure 5).

Figure 5: The "hanging garden" at Casa del Agua: lettuce growing out of PVC pipes.

Figure 5: The "hanging garden" at Casa del Agua: lettuce growing out of PVC pipes.

Both harvested rainwater and graywater were tried for flushing toilets in this project. However, after the local plumbing code made the use of low-flow (6 liters per flush) toilets mandatory, the use of rainwater and graywater for flushing toilets did not seem necessary, especially since people do not feel comfortable having "unclean" water in the toilet bowls.

Water-use activities in Casa del Agua were closely monitored to achieve a better understanding of water utilization in the project. A central monitoring compartment was installed in the project, and meters were installed on all the outside hose bibs. Ten meters were installed in the central monitoring compartment on the lines for drip irrigation to the lawn area and planter beds, evaporative cooler supply, and both input and output of the graywater and the harvested rainwater. Also, the collection and consumption of graywater and harvested rainwater was physically measured by using marked dipsticks inserted into the storage tanks.

The dissemination of knowledge concerning water conservation methods and practices was a major component of the Casa del Agua project. Therefore, the project was provided with a public information center, and the house garage was adapted to serve this function. The media also helped convey information to the public about the house as a water-conserving project. The occupants of the house also took a part in the public education and awareness aspect of the project. In fact, one of the responsibilities of the occupants of Casa del Agua was to document how much water was used and where it was used. Moreover, every Sunday, the day during which the project was open to the public from one to four o'clock in the afternoon, the resident family would accompany visitors on a walking tour of the outside of the house. The family would also give a brief overview of the project and the water conserving systems it incorporates, and would explain the experiments taking place in the house and how successful they have been. Professional presentations were also made in the information center. In addition, one of the residents was doing his master's thesis on educating the public regarding water conservation, and his research revealed that one-half of the people who visited Casa del Agua implemented some of the ideas presented to them during their visit. The study also noted that this house contributed to a dramatic increase in water conservation awareness among the general public. (6)

According to Brittain, the results of the project showed that the amount of water used at Casa del Agua is 24% less than that used in a typical average Tucson single-family residence (the average family in Tucson is about 2.5 persons). The typical average single-family house in Tucson uses about 428 liters per person per day. That amount was reduced in this particular project to 326 liters per person per day. Also, a reduction of 47% in the use of municipal water use was achieved. The amount of municipal water used at Casa del Agua was 227 liters per person per day; the amount of graywater used was 61 liters per person per day; and the amount of rainwater used was 34 liters per person per day. 69.7% of the total water used was municipal, 19.9% was graywater, and 10.4% was rainwater. No municipal water was used for irrigating the garden or for the evaporative cooling system. (7)

Brittain believes that considerable success had been achieved through the Casa del Agua project, which encouraged further experimentation such as the implementation of the Desert House project in Phoenix, Arizona.

Desert House

In 1993, the Desert House demonstration project opened to the public. The project, which consists of a three-bedroom single-family home and an adjoining information center, is located at the Desert Botanical Garden in Phoenix, Arizona (figures 6 and 7). The location of the project is ideal since about 200,000 persons visit the Desert Botanical Garden each year. The Desert House also draws additional visitors to the garden through the publicity associated with it. The house was perceived as an example for improving residential water and energy efficiency. Its objective was to achieve a 40% reduction in water and energy use in comparison to the typical three-bedroom single-family house in the Phoenix area.

Figure 6: A view of the Desert House demonstration project and its surrounding context in the Desert Botanical Garden in Phoenix, Arizona.

Figure 6: A view of the Desert House demonstration project and its surrounding context in the Desert Botanical Garden in Phoenix, Arizona.

Figure 7: The layout plan of Desert House.

Figure 7: The layout plan of Desert House.

The Desert House is about 149 square meters in area. It cost about 125,000 $US to build, which was the cost of the average home in the Phoenix area at that time. It was designed with the main axis running along the east - west direction, and it had a minimal number of windows along the eastern and western facades to reduce heat gain from the morning and afternoon sun. The southern side of the house was provided with the highest window area since that side would collect solar heat in winter but could easily be shaded during the summer. Moreover, a ramada was built along that side and deciduous vines were planted next to it (figure 8). The ramada and vines provide protection from the sun in the summer, but the vines lose their leaves in the winter and allow the sunlight to enter and heat the house. A minimum number of northern windows were included in the house to minimize heat loss in the winter. Instead, the rooms located along the northern side of the house were provided with clerestory windows along their southern side so as to let the sunlight reach them.

Figure 8: A view of the ramada and adjacent vines installed at the south side of Desert House.

Figure 8: A view of the ramada and adjacent vines installed at the south side of Desert House.

Graywater and rainwater storage tanks were located in the basement of the house. Brittain mentioned that the basement in this particular project was referred to as the "research basement" because it houses all the plumbing equipment, water meters, control-valves, storage cisterns, and pumps. The water meters also are connected to a computerized monitoring system that monitors the resident family's use of water. Two 18 cubic-meter tanks were assigned for graywater storage and one 18 cubic-meter tank was assigned for rainwater storage. Brittain mentioned that the Desert House project team benefited from the knowledge they had gained in the Casa del Agua project. Consequently, they knew that significant graywater storage was needed in order to get through the dry period between the two rainy seasons of winter and summer, and that rainwater harvesting, although necessary, would not be enough. Each of the storage tanks for graywater and rainwater storage consists of four pre-cast concrete sections, which were connected together and sealed. The tanks are accessible through manways in their lids.

The Desert House was provided with a water-conserving landscape design. The house was surrounded by a path network so that visitors would be able experience the landscaping and to look at some of the features that were used for shading the house. The soil was mulched and low-water-use plants were used so as to contribute to the reduction of water use at the house. The garden plants were irrigated with graywater or rainwater, depending on the type of plants. The landscaping incorporated a small lawn area in the backyard, which served as an activity zone. Each of the plants, as well as the components of the irrigation system, were labeled so as to be identified by visitors.

In addition to the exterior pathway, the project incorporated two interior display areas. The first is the technical exhibit that is housed in the garage attached to the home; the second is the information center that is housed in a separate building. The technical exhibit deals with the technological aspects incorporated in the project, as well as other equally appropriate alternatives. These include items such as the showerheads, toilets, faucets, drip irrigation, as well as graywater recycling and rainwater harvesting systems. The exhibit also deals with the building materials used in the Desert House. These include appropriate types of glass, insulation materials, walls, and heating and cooling equipment. The idea of exhibiting a variety of materials aimed at illustrating to the public the multiplicity of water and energy efficient designs that can be used. This technical exhibit also is provided with an interactive computer that features a three-dimensional model of the house. One would select an area in the house featured on the model, and the computer would display how much water or energy is being consumed in that area (figure 9).

Figure 9: The technical exhibit at Desert House: the interactive computer.

Figure 9: The technical exhibit at Desert House: the interactive computer.

On the other hand, the information center illustrates the goals of the project, why one needs to conserve water and energy, and how one can design water and energy efficient structures and landscapes. It contains a model of the Desert House and a simulation of the positions of the sun at the different times of the year and the day. This allows visitors to better understand the importance of orientation for a given structure, and the importance of shading devices and of the correct placement of windows (figure 10). The information center is also equipped with a seating area for lectures and presentations. After all, the project addresses the community, and "... is designed to educate the community about the importance of wise water and energy use, and about the practicality of creating more resource-efficient housing at an affordable cost without significantly impacting today's lifestyle expectations." (8)

Figure 10: The information center at Desert House: the model of Desert House and a simulation of the positions of the sun at the different times of the day and different times of the year.

Figure 10: The information center at Desert House: the model of Desert House and a simulation of
the positions of the sun at the different times of the day and different times of the year.

Questions and Answers

One issue discussed following Brittain's presentation was how storing graywater for extended periods of time affects its quality. Brittain mentioned that graywater becomes cleaner the longer it is stored in tanks. This is because of the process of "anaerobic digestion" in which the particles found in the graywater keep digesting themselves. The same applies to rainwater in a storage tank. Rainwater is dirtiest immediately after rainfall since debris and bird droppings go into the tank. But with time, the litter settles down, the process of anaerobic digestion takes effect, and the water becomes cleaner. Brittain added that in both Casa del Agua and Desert House, the drip irrigation systems that distributed rainwater or graywater were never clogged.

A follow up question was whether graywater was unhealthy, and therefore should be treated through processes such as aeration or chlorination. Brittain answered that the plants seem to thrive on the nitrogen and the nutrients found in graywater, and that graywater therefore seems to function as a natural fertilizer. He added that the research he and his colleagues undertook also showed that soaps did not cause any problems. They tried to avoid using soaps containing borax and similar materials that may harm the plants. However, the researchers did not notice any negative signs resulting from using the graywater for irrigating plants during the operation years for the two projects.

Another question enquired as to why mixing graywater with rainwater had not been tried in Casa del Agua and Desert House. Brittain answered that this was because each project included ornamental plants, a herb garden, and a vegetable garden. The project team wanted to control the quality of the water being applied to each of these plant groups. Graywater is best suited for shrubs, trees, and lawn. On the other hand, rainwater is of a higher quality in terms of cleanliness, and therefore was applied to vegetables and herbs. Brittain added, however, that additional research should be carried out regarding the use of graywater for watering certain vegetable crops.

Brittain was asked whether one should provide two cisterns for the harvested rainwater so that when cleaning one cistern, its content of water can be drained to the second cistern rather than being discharged to the sewer system. Brittain agreed that the idea of having two cisterns for the harvested rainwater could be of use, but did not believe it necessary. He added that such tanks rarely need cleaning. In fact, he has crawled down into the rainwater storage tanks of Casa del Agua and Desert House, and has found them to be adequately clean. He did find silty deposits at the bottom of the tanks, but water is pumped out of those tanks from about 160 mm above the bottom, which is above the layer of silt. Brittain added that he crawled into a rainwater cistern that had been in operation for about sixty years, and there was hardly anything in it that really needed cleaning. Still, he agreed that when more than a single storage tank is available, one has the option of draining the content of one cistern into the other if a leak or another problem occurs.

One audience member discussed the economic aspects of installing rainwater and graywater tanks as well as a dual plumbing system in a typical house. He mentioned that municipal water in Jordan is relatively cheap (at least for those who use small amounts of water), while the costs of installing such systems is considerable. He added that the money saved through the use of recycled graywater and harvested rainwater might not be extensive. Since people would not save much through the installation of such systems, they would rather not use them. He wondered if the economic logic for installing rainwater harvesting or graywater reuse systems in a place such as Arizona was more convincing than he expects it to be in Amman.

As a response to this point, Brittain emphasized that harvesting and reusing water is an ethic. Rainwater is water of very high quality, and graywater is a source that is always available: a source that one always can count on. In Arizona, municipal water is very inexpensive. Therefore, in order to encourage people to implement graywater and rainwater harvesting systems, researchers need to look at simple and economically affordable solutions. Brittain mentioned that in some cases people have been using 208-liter drum tanks located above surface for collecting rainwater and graywater, instead of the more costly underground tanks. When one values a system, one will find a way to put it in use. In addition, the implementation of rainwater harvesting might be "need-driven." Brittain added that many people in Tucson even have much simpler systems than the ones he showed in his presentation.

Brittain also highlighted cases where people must use all the water sources available to them. He mentioned that he visited islands where there are no fresh water sources, and people have to desalinate their water. The value of water in such areas therefore is much higher than in other contexts. Often, the cost of drilling wells to reach underground fresh water tables is prohibitively expensive. In such a case, Brittain believes that one would start looking at the value of harvested rainwater and graywater in a totally different way. For example, he mentioned that in certain Islands in the Caribbean, where harvesting rainwater is the only source of water, the inhabitants build their roof in a way that would harvest the highest amount of rainwater. Consequently, they extend their porches as far as possible so as to maximize the amount of collected rainwater that is directed into the cisterns located in a basement underneath the house. Brittain added that in this particular case one is not dealing with a simple "economic incentive," but with a "survival incentive." When there is a shortage in water resources, people should start thinking of the issue of rainwater harvesting and graywater reuse differently, a matter that applies to many locations in the world, including Jordan.

Another question asked as to why a minimum number of northern openings were used in the design of Desert House. It was added that, to the contrary of what was applied in the Desert House, it is often thought that in hot climates one would increase openings in the northern side where solar heat gain is at its lowest. Here, Brittain stressed his view that northern windows should be avoided. He added, however, that exceptions might be made in cases such as the availability of an exceptionally beautiful view along the north side of the house. Brittain mentioned that the path of the sun in the winter and summer is to the south: in the summer time the sun path is at a high angle, so very slight overhangs can shade southern windows and keep the sun out. In fact, southern windows are the easiest to shade and protect, and one can always mitigate the extreme glare one usually gets from southern windows through green groundcovers and through black shade cloth on the roof in front of clerestory windows. On the contrary, a window that is placed along the north side, even the highest efficiency window, is just "a hole in the wall," and the bigger that window is, the more heat is lost through it in the winter months. A room with northern windows will be very cold during the winter, and during the summer when the temperature in Tucson is 110 degrees Fahrenheit (about 43 degrees Celsius) that window would bring in heat. Thus, in order to create truly energy efficient designs, one should place properly sized windows along the southern façade, and minimize windows along the western, eastern, and northern facades.

A follow up question inquired about calculating the proper window size. Brittain mentioned that through his experience in designing passive solar homes and through the use of computer simulations for window designs, he recommends in the Tucson area that the south glass area only occupy 8 - 10% of the floor area of a given space. Consequently a 10 square-meter room ideally should have about 1.0 square meter of glass located along its southern side. Brittain added that designing a passive solar home with too many windows to the south would bring about the same problems he mentioned when placing windows along the northern facade. Too much heat is lost through such windows in the winter, and too much heat is gained through them in the summer. Brittain also pointed out that as one moves into colder climates, where more heat is needed, one might be able to raise the ratio of glass area to floor area. However, in that case, one might need to protect the additional glass with insulating curtains at night to minimize heat loss.

Brittain was asked to elaborate on the issue of using harvested rainwater for cooling purposes. Here, Brittain mentioned that evaporative coolers are very common in Tucson since they are very suitable for hot dry climates. The evaporative cooler releases heat from the incoming dry air, and then distributes cooler, humid air onto the house. However, they are very high water users, and researchers have been looking at harvested rainwater as a source of water for them. The advantage of using rainwater for evaporative coolers is that it is a relatively mineral-free water source compared to the municipal water supply, which is pumped from very deep in the ground. The salts found in the municipal water build-up on the cooler pads, and thus reduce their ability to produce cool air. Since rainwater is softer than municipal water, it does not result in salt build-up on the cooler pads, and therefore provides for more efficient cooling and less annual maintenance.

Another question enquired about the construction of the pre-cast concrete tanks that were installed in the Desert House project. Brittain mentioned that there is a company in Phoenix that casts huge tanks with a storage capacity of up to 30 cubic meters. Those tanks are produced in four pieces, a bottom, two middle rings, and a top, which together form a cube. The top and bottom sections look like an "open box." The lower sections are provided with a groove along the open side, and the upper section is provided with a tongue along the open side. The two sections are placed together by having the tongue fit into the groove. A special mastic is placed in the groove before the upper section is set down on it. This causes the mastic to ooze out, so the excess mastic is then cut off. Cracks in the concrete then are filled with expansive cementitious grout, and the whole internal surface of the tank is coated with a sealer.

Brittain was asked to illustrate the construction materials that he often uses for walls and ceilings in his energy efficient designs, and whether he uses concrete slabs with cavities in them for the roofs. After all, it is through roofs that much heat is gained in the summer and lost in the winter. Brittain mentioned that he always tries to achieve an R rating of 30 or more for the roofs he designs. (9) He added that he often uses lightweight structural insulated panels, which have urethane insulation in the middle and nailable surfaces on the top and the bottom. Also, he mentioned that he does not recommend heavy concrete roofs for Arizona, where earthquakes need to be taken into consideration. The situation is different in Jordan where vertical extension of homes is often expected as families expand. Consequently, it makes sense in Jordan to use heavy concrete roofs that would later also serve as floors.

As for the use of walls in energy efficient designs, Brittain mentioned that in the Desert House, for example, the walls were built of 20 cm-thick concrete blocks that have been developed in Arizona, and that are known as Superlite "Integra mass blocks." The blocks are H-shaped, and therefore are open on the ends. This means that minimal heat conduction takes place between the outside and inside faces of the block. The blocks are insulated with foam insulation between their inner and outer surfaces, yielding a rating of R-25. The windows that were used in the Desert house are dual-pane windows with a "heat mirror" film between the panes, and provide an R rating of 3 plus.

The last question enquired whether the concepts of water conservation, which Brittain demonstrated through the two residential examples of Casa del Agua and Desert House, have been applied in commercial and industrial buildings. It was noted for example that car-washing stations are big users of water, and therefore should be subject to water conserving regulation codes. Brittain asserted that in Arizona there are water conservation regulations for commercial and industrial buildings. For example, any commercial or industrial property that uses 10 acre-feet of water a year has to conform to a different set of regulations than smaller properties, and must recycle water and reuse it a certain number of times. (10) In fact, the standards regarding water conservation that are applied to such large properties are much more rigorous than those applied to residential properties.

Brittain added that Phoenix regulations prohibit, for example, discharging rainwater from large-scale shopping malls into the storm sewer system. Instead, all rainwater should be detained on-site. Consequently, culvert systems are used to harvest rainwater from areas such as parking lots and walkways. The culverts consist of a large network of underground pipes with diameters of up to 4 meters. The pipes are interconnected and they can either be perforated, so that they leak water out into the ground, or they can retain that water as storage tanks. Interestingly enough, Brittain mentioned that in spite of the use of this culvert system, the collected rainwater most often is not used for irrigating the landscapes on these properties. Instead, those landscapes are still being watered with municipal water because it is so inexpensive. Brittain added that harvested rainwater should not be looked at as something to be disposed of, but rather should be looked at as an asset. He added, however, that good examples of using harvested rainwater in Arizona at a large scale do exist.


 (1) Richard Brittain is an Assistant Research Professor in the School of Architecture at the University of Arizona. He teaches courses in desert architecture and architectural photography, as well as design-build studios. His private practice focuses on residential desert architecture, utilizing adobe and rammed earth wall materials, passive solar energy efficiency, and water conservation techniques with rainfall harvesting and graywater reuse systems. For additional information on Richard Brittain, see

 (2) The amount of rainfall in Amman ranges from 300 mm in the eastern parts of the city to about 500 in its western parts. The relationship between the two rainfall patterns, the unimodal of Amman and the Bimodal of Tucson, was discussed in a public lecture entitled "Creating Landscapes In Water-Scarce Environments: A Case Study Of Tucson, Arizona" presented by Margaret Livingston at Darat al-Funun in Amman in May, 30. For additional information on this subject, see the documentation of the lecture in the e-publications section of this web site.

 (3) For a complete list of the participants in the project, see note 7 below.

 (4) For more information on low-water-use plants and drip irrigation systems, see the documentation of Livingston's lecture, "Creating Landscapes in Water-Scarce Environments: A Case Study of Tucson, Arizona" in the e-publications section of this web site.

 (5) Harvested rainwater has been used historically for drinking and irrigation. With urban development, large centralized water supply systems have replaced individual water harvesting systems. However, people more recently have become reacquainted with water harvesting as an effective water conservation tool that provides free water independently from the municipal supply. Water harvesting also reduces off-site flooding and erosion by holding rainwater on site. In addition, passive water harvesting (which also is discussed in this essay) forces salts down and away from the root zone of plants, thus allowing for greater root growth.

For more information on rainwater harvesting, see Harvesting Rainwater for Landscape Use (Tucson: Arizona Department of Water Resources, 1999). This document is available online through the web site of the Water Wiser program of the American Water Works Association. The web site also includes a list of references related to the subject of rainwater harvesting and graywater reuse, as well as full texts of manuals and books on these subjects. In addition, the web site of the American Water Works Association provides downloadable publications relating to water harvesting.

 (6) See Glenn France, Evaluating the Effectiveness of a Community Water Conservation Demonstration / Education Project: Casa del Agua, Tucson, Arizona (Master's Thesis, University of Arizona, 1989).

 (7) For additional information on the Casa del Agua project, see Richard Brittain, K. James Cook, Kenneth Foster, Glenn France, Susan Hopf, and Martin Karpiscak, "Casa del Agua: Water Conservation Demonstration House - 1986 through 1998," Journal of the American Water Resources Association 37-5 (October 2001): 1237 - 1248.

 (8) For additional information on the Desert House project, see Richard Brittain, Kenneth Foster, and Martin Karpiscak, "Desert House: A Demonstration / Experimentation in Efficient Domestic Water and Energy Use," Water Resources Bulletin 30-2 (April 1994): 329 - 333.

 (9) The R-factor refers to "unit thermal resistance," which is the thickness of the element divided by the thermal conductivity of the material of which it is made.

 (10) An acre-foot is the volume of water that would cover one acre (about 4,000 square meters) to a depth of one foot (30.5 cm). This would amount to 1220 cubic meters.

List of Figures*

Figure 1: A view of the Casa del Agua demonstration project in Tucson, Arizona.
Figure 2: A view of the backyard of Casa del Agua that shows the concrete paving and extended rooftop.
Figure 3: The installation of the underground rainwater storage tanks at Casa del Agua.
Figure 4: The landscaped area above the underground rainwater tanks at Casa del Agua: lawn area, Mesquite tree, and potted plants placed on the tanks' access manways.
Figure 5: The "hanging garden" at Casa del Agua: lettuce growing out of PVC pipes.
Figure 6: A view of the Desert House demonstration project and its surrounding context in the Desert Botanical Garden in Phoenix, Arizona.
Figure 7: The layout plan of Desert House.
Figure 8: A view of the ramada and adjacent vines installed at the south side of Desert House.
Figure 9: The technical exhibit at Desert House: the interactive computer.
Figure 10: The information center at Desert House: the model of Desert House and a simulation of the positions of the sun at the different times of the day and different times of the year.

 * All images are courtesy of Richard Brittain.