Graywater Reuse in Other Countries and its Applicability to Jordan -- continued --

3.0   Issues about Graywater Reuse

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3.1   Graywater Quality

The quality of graywater varies depending on the source of the water, and the uses to which the water has been put. The following table indicates the likely constituents of water from various household sources.

Various studies into graywater quality in different countries have been published. The following table gives an overview of some of the parameter concentrations, together with some guideline parameters taken from a number of sources.

Table 3.2:  Graywater Quality Characteristics

BOD5: biochemical oxygen demand – a measure of the amount of organic matter.  It specifically measures the amount of dissolved oxygen that microorganisms use in a water sample to break down organic material at 20 degrees Celsius over a 5-day period.  Clean waters have BOD5 values < 1mg/l and rivers are considered polluted if the BOD5 is > 5 mg/l (Kiely 1997).  Acceptable BOD5 values range according to country and intended use.  For example, Jordanian standards (JS 893) allow BOD5 values of < 150 mg/l for the irrigation of fruit and forestry trees and crops.

SS:  suspended solids – measure of the amount of solid matter

PH: a measure of acidity or alkalinity (less than 7 is acidic, greater than 7 is alkaline)

EC:  electrical conductivity - a measure of all dissolved salts in the water, and therefore a measure of salinity hazard. The higher the concentration of salts and minerals, the greater the potential for adverse impacts on the soil and plants. A standard classification of soils related to salinity is as follows:

Class Specific Conductivity (micromhos/cm (µS/cm)): 
0.   Non saline, 0 - 2,000
1.   Very slightly saline, 2,000 - 4,000
2.   Slightly saline, 4,000 - 8000 
3.   Moderately saline, 8,000 - 16,000 
4.   Strongly saline > 16,000

If the EC in water increases on a frequent basis, and for a prolonged period of time, certain sensitive plants could suffer salt injury (Bennett et al. 2002).

FCC: fecal coliform count – a measure of the degree of bacterial contamination from humans and animals.  Certain standards allow < 1000 CFU (colony forming units)/100 ml in the water used for crop and tree irrigation (Leggett et al. 2001a).

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Most graywater is used to irrigate plants, so the most immediate risks of pollutant constituents in the graywater are related to plant health. It is assumed that users will avoid the disposal of inappropriate substances (paints, antifreeze, solvents, mothballs, wastewater from oily rags, chemicals from photo-labs, etc) into the graywater. However, many graywater sources themselves will contain substances which may have harmful effects.   

Laundry products in particular use a variety of chemicals that can be harmful to plants. Most soaps and detergents - including baking soda - contain sodium compounds.  High levels of sodium can cause discoloration and burning of leaves, and can contribute toward an alkaline soil condition. In addition, high sodium can be toxic to certain plants and can prevent calcium from reaching the plants (the UN Food and Agriculture Organization (UNFAO) indicates “no problems” at sodium levels of < 69 mg/l, “increasing problems” at levels of 69 – 207 mg/l, and “severe problems” at levels of > 207 mg/l) (Bennett et al. 2002).  A second possible effect of some types of sodium is a disturbance of the soil’s ability to absorb water. The sodium adsorption ratio (SAR) is the parameter that measures the effect on the soil structure of sodium compounds.  A high SAR (13 or above) will result in soils with reduced permeability and aeration, and a general degradation of the soil’s structure. A buildup of sodium over time therefore will reduce the soil’s ability to support plants. This is probably one of the most serious potential long-term consequences of irrigation with graywater. Reduction in the amount and concentration of sodium in the graywater – either by reducing the amount of detergents and soaps used or by using reduced-sodium products (to be discussed further later) will reduce the risk to plant health and soils. Also, flushing of the soil by freshwater or rainwater from time to time will reduce the build up of sodium in the soil. Water softeners also introduce sodium-based compounds into the water, and should be avoided where graywater is to be reused. 

Detergent and laundry products also contain other chemicals that are harmful to plants such as boron, chlorides, peroxides, and petroleum distillates.  Boron, for example, is very toxic to most plants. Plant damage from excess boron first shows up as “burning” of leaf edges. Other symptoms of boron toxicity include leaf tip and margin burns, leaf cupping, chlorosis, branch dieback, premature leaf drop, and reduced growth (UNFAO indicates “no problems” at boron levels of < 0.75 mg/l, “increasing problems” at levels between 0.75 and 2.0 mg/l, and “severe problems” at  levels > 2.0 mg/l) (Bennett et al. 2002). On the other hand, most hand and dish soaps and shampoos used in normal residential concentrations will not damage plants (Ludwig 1995-1999). In general, gentle soaps, such as soap flakes, are more suitable than those heavily laden with lanolin, perfumes, and other chemicals. Soaps are less harmful than detergents. However, the use of any soap or detergent product may present problems over periods of sustained graywater application. If salt buildup in the landscape is a concern, it is better to use liquid detergents than powdered detergents. Powdered detergents contain excessive amounts of sodium compounds, which is often used as a ‘filler’ ingredient not essential to clothes cleaning. Many detergents also contain phosphate compounds, but these are a nutrient to plant growth, and will generally benefit the plants. 

Bleaches commonly contain chlorides, which can damage plants, particularly if the bleach water actually touches the foliage. One symptom of chlorine-induced damage is a tendency for new, expanding leaves to appear bleached (UNFAO indicates “no problems” at chloride levels of < 142 mg/l, “increasing problems” at levels between 142 and 355) mg/l, and “severe problems” at levels > 355 mg/l) (Bennett et al. 2002). Bleaches carry large amounts of chlorine.  Therefore, ammonia is often used as a substitute for bleach, as it also cuts grease and is preferable as a household cleaning and deodorizing agent. Ammonia itself may cause damage to plants, although it quickly oxidizes to nitrates and nitrites - themselves plant nutrients - in certain soil conditions. Although kitchen sink water is often prohibited for reuse, few of the constituents of kitchen water cause problems for plants. Organic material and bacteria are generally broken down in the soil, and do not harm plants.

3.3   Keeping the Plants Healthy  

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Plants irrigated with graywater should be monitored regularly for symptoms of damage. If any signs of plant injury appear, use of graywater should be discontinued or reduced. ‘Burning’ of leaf edges may be caused by excess salts in the water. Acid-loving plants may experience some chlorosis or yellowing of the foliage, due to the alkaline nature of the graywater.

If plants appear to be injured, the surrounding area should be flushed with fresh water. If possible, application of graywater should be rotated with fresh water for susceptible lawns and fruit trees. In addition, graywater should be applied over a broad area to avoid build up of harmful ingredients in one particular location. Applying graywater to the same plants all the time should be avoided. Particular care should be taken with water containing detergents, bleach or boron, and the use of rinse water containing fabric softeners should be avoided whenever possible.

Graywater can be used for ornamental trees and shrubs. However, applying the water directly to foliage or stems should be avoided, as most of the feeder roots responsible for absorbing water are located at the base of the plant. Graywater poured directly on the base of trees and shrubs could encourage crown rot. It is best to distribute the water over the whole root system, where it will be most efficiently used.

Graywater should only be used on well-established plants, not on seedlings or young plants as they are more sensitive to the impurities in the graywater. Graywater generally should not be used on potted plants because of possible build up of contaminants in the soil that can damage the restricted root systems in a confined volume of soil. In addition, graywater should never be applied to root crops or leafy vegetables that will be eaten raw, such as carrots, lettuce, or herbs, and it should not come in contact with the edible portion of fruits and vegetables (for instance, with root vegetables, such as radishes, potatoes, and beets). Use of graywater with fruit trees, and other plants where the edible portion is well away from the water, is permissible.

If graywater is used for irrigating food plants, its application should be restricted to the soil surface around plants of which only the above ground part is eaten. Graywater should not be poured directly on plant leaves. Sprinklers should not be used in order to avoid contacting the above-ground portion of the plants. Surface irrigation should not be used for food plants, except for fruit trees. Graywater should be cool before being used since hot water can damage plant roots and stems.

Soil pH (acidity or alkalinity) is very important because it influences several soil properties that directly affect plant growth, and also has a bearing on soil bacteria and nutrient availability. Plants have a range of tolerance to pH, but most plants grow best in soils with a pH between 5 and 7. Plant nutrients generally are most available in the pH range of 5.5 to 6.5, which is also a good range for beneficial soil bacteria. When the soil pH is 5 or below (i.e. strongly acidic), nitrates, phosphates and potassium become less available to plants, earthworms disappear and bacteria become less active. Particularly alkaline soils also lock up vital mineral nutrients needed for plant growth. When the pH is 8 or higher (i.e. moderately or strongly alkaline), iron and zinc become less available to plants. Chlorotic leaves develop, and salt burn from sodium and boron tend to occur. Certain plants will be particularly susceptible to damage from graywater, particularly acid-loving plants.

Click here to view a list of plants that are recommended for irrigation by household graywater.