April 1977 RAIN Page 11 Experiments at the Farallones (Jrban House indicate tbat Wasteuater treatment for a single family can be mucb simpler Tbe following are excerpts from a four-page Gtey Water Fact Sheetprepared by Tom Jaaits and I'om Fricke and aaailable for $1 from tbe Farallones Integral (Jrban House, 1516 Fiftb Street, Berkeley, CA 94210. How much grey water can be used in an urban garden? Use only as much grey water in your garden as is required for reasonable irrigation; scale your waste water recycling effort to suit your garden water requirement. A good, safe ru1e is that a square foot of loamy garden soil, rich in organic matrer, is capable of handling one-half gallon of grey water per week. Sandy, well-drained soils will accommodate more warer; clayey, poorly-drained soils less. If your garden area suitable for grey water application is 500 square feet, then up to 250 gallons of waste water may be discharged each week. This rate might be greater during the summer months when surface evaporation and plant transpiration is considerable and less during the winter, when evapotranspiration is minimal. Frequently check soil moisture ro determine precise application rates for your garden. Follow these suggestions for sound waste water application: 1. Apply the grey water to flat garden areas; avoid slopes where runoff might be a problem. 2. Use the waste water on mature vegetation or well established vegetable plants rather rhan young plants and seedlings. 3. Minimize waste water application to acidJoving plants such as rhododendrons and citrus since waste water is alkaline. 4. To the extent possible, disperse the grey water application over a large garden area. 5. When available use fresh water for garden irrigation on a rotating basis with grey water to help cleanse the soil of sodium salts. 6. Apply thick compost mulches to areas receiving grey water to improve natural decomposition of waste residues. What about soaps and detergents? Are they harmful to the soil and plants? As a general rule, soaps are less harmful than detergents, but either presents potential problems over periods of sustained use of grey u,ater containing them. The common problem of soaps and derergents is that they both contain sodium, an element whicrr in excessive amounts is harmful to soils (de, stroys soil aggregation) as well as to plants (induces tissue burn). The best strategy is to minimize rhe usc of cleaning materials, and wherever possible choose soaps rather than detergents. Gentle soaps, such as soap flakes, are preferred to those heavily laden with lanolin, perfumes and other chemicals. Where detergents must be used, select those which do not advertise their "softening powers" (softeners are rich in sodium-based compounds). If you plan on reusing washing machine water, bleach should be minimized or eliminated, and boron-based (Borax) detergents absolutely avoided. Phosphates in detergents are not as great a problem in soil application as they are in sewage discharge inro water bodies; nevcrtheless, low phosphate detergents are prefe rable. Ammonia is acceptable in reasonable amounts. USINGGREYWATER IN YOURGARDEN How should the grey water be applied to the garden? Apply the waste water directly to the soil; do not overhead sprinkle or allow the waste water to conract the above-ground portion of food plants. Waste water is best conveyed tothe garden by a standard 3/4-inch garden hose. A central hose may feed several laterai short hoses by way of a "y" junction such that the waste water is distributed evenly over larger areas of soil. The lateral arms should be rotated around the garden frequently to reduce the possibility of localized flooding or excessive residue buildup. At the end of each hose lateral, artach (by hose clamp) a cloth bag (cotton or canvas), to intercept particulates and soap residues conveyed in the grey water. The bag will allow for dispersed water outflow while trapping undesirable materials. The bag should be removed periodically, washed, turned inside out and allowed to sun-dry, and re-used. Must any precautions be taken to protect against damage to the soil from sustained use of grey water? Over extende d periods of grey water application, sodium may build-up in the soil resulting in poor soil drainage and potential damage to plant tissue. High levels of sodium may be detected by conducting a pH test of the soil using litmus paper (obtained from a pharmacy or nursery). If the pH reading exceeds 7.5, the soil has become overloaded with sodium. Correct the problem by spreading gypsum (calcium sulfate) over the soil at a rate of 2 pounds per 100 sq. ft. per month. Continue treatment until the soil pH drops to 7.0. As a precaution against furthe r sodium buildup, gypsum may be applied to the soil at a rate of 3 pounds per mo.ntb for every 50 gallons per day discharge ro rhe area being watered. Normal dilution of waste water by rainfall and/or fresh water irrigation will help to cleanse the soil of the sodium. When available use fresh wate r for garden irrigation on a rotating basis with grey water Is there any danger of pathogen transmittal by using grey water in the garden? Waste water from the shower, bath tub and washing machine can conceivably contain human pathogens (disease-causing organisms). However, when the grey warer is discharged to the soil, potentially harmful viruses and bacteria are quickly destroyed by the abundant soil organisms better suited to the soil environment. Also, if the pathogens were to survive, it is unlikely that they would be assimilated by the plant roots and translocated to the edible portion. Nevertheless, if you are particularly suspicious of the sanitary quality of your grey water, do not apply it to root crops which are eaten uncooked, or perhaps only to soil in which ornamental plants are maintained.
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