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Questions about gray water; is it safe, legal? How can you collect and use it in your garden?

Faced with severe water rationing, what can you do to help your garden survive? If other conservation measures don't stretch your water far enough, you may have one more option: gray water. The term refers to household water recycled from showers, bathtubs, bathroom sinks, and washing machines. Collected from all of these sources, gray water can supplement your garden's water supply by as much as 100 gallons per person per week.

Some household water isn't fit for reuse. For instance, the water from kitchen sinks and dishwashers is contaminated with grease and food particles. Toilet wastewater is called "black water," and should never be collected. (On the other hand, runoff from taps collected while the water warms up is considered clear water.) Even the use of "clean" gray water raises safety concerns, but laws have been changed to permit its use. Here, we examine the issues of both safety and legality, and we offer some guidelines on how to collect and distribute gray water to the garden as prudently as possible.

Is gray water safe?

The primary concerns about gray water stem from the fact that its quality can be highly variable and it may contain unhealthy bacteria and viruses. (It's worth noting that, according to health officials we consulted, there are no documented cases of illness caused by gray-water use.) The health risks from gray water are minimal if you handle and apply it properly. Never collect wash water contaminated by soiled diapers, people with infectious diseases, or poultry or wild game preparation. Also, avoid using greasy, soapy water full of suspended solids.

Follow five basic precautions when using gray water. Always use it the same day it's collected. Don't apply it where people will come in contact with it, such as on a lawn. Don't let it puddle or stand without being absorbed quickly. Don't spray it or sprinkle it in any way. And whenever you handle gray water or equipment that's in contact with it, wear rubber gloves.

Is it legal?

In the past, health officials have frowned on the use of gray water. But with water supplies growing increasingly short, some are allowing more leeway.

Santa Barbara County Supervisors recently amended the local building ordinance to allow the permanent use of gray water and to allow (with a permit) minor modification of waste-water pipes to collect it. Tucson, Arizona, water department staff and state health officials are now working to come up with usage guidelines. Most other Western communities have no laws specifically about gray water-although most building codes prohibit alteration of household plumbing without an inspection and a permit. For specific rules in your area, call your county health department (in the county government listings in your telephone book, look under Health Services Department or Environmental Health Services). What can you use it for?

Many of our readers report that they've been using gray water on their plants since the 1976-77 drought with few side effects. Most plants thrive on gray water and will not be affected by mild dish soaps, hand soaps, or shampoos.

You can use gray water to irrigate fruit trees and ornamental plants but never use it on vegetables or to sprinkle lawns or wash paved surfaces. In general, don't apply it to seedlings, container plants, or acid-loving and salt-sensitive plants such as azaleas, tuberous begonias, camellias, citrus, ferns, gardenias, hydrangeas. Biodegradable soaps are usually the least harmful. And liquid detergents tend to be less harmful (have less sodium) than powdered ones. Avoid strong chemicals-such as those designed to open clogged drains-and products containing boron, chlorine, or sodium. Water softeners use sodium; in dry-winter areas, avoid collecting water that has run through one. Even if you're careful about product use, small amounts of sodium and other potentially harmful substances may still build up in the soil and raise the soil's pH, especially if heavy rains don't come this winter (a soil test can determine sodium content and pH levels). To help leach harmful substances away, you can alternate irrigations between fresh and gray water or flush the soil twice a year with a heavy sprinkler irrigation. To lower the pH, work in 3 to 5 pounds of finely ground soil sulfur per 100 square feet and till in plenty of organic matter.

In clay, sodium can also make soil sticky and hinder drainage. Spade into the top several inches of soil 5 to 10 pounds of agricultural gypsum per 100 square feet.

How much gray water can you expect-and how do you collect it?

Washing machines supply 30 to 40 gallons of water per load. For showers, low-flow heads range from 2 to 3 gpm (gallons per minute), standard heads from 5 to 8 gpm. Weekly average for each bathroom sink is about 14 gallons per person. To figure out bow many-and which-sources to tap into, and how many collection tanks you need, determine the water needs of your plants (your cooperative extension office may be able to help).

Pictures on pages 172 to 175 show several ways to collect gray water. Before constructing your own system, check local building codes. If you alter plumbing, you may want to seek professional advice (alterations must be approved by a building inspector). Always provide for overflow into the sewer line in case the gray-water system backs up, but install a swing check valve between the tank and the sewer line to prevent sewage backup into the tank. The easiest and least expensive collection system to install is one like that pictured on page 172 connected to the washing machine. If the tank sits below grade or the garden slopes up above the outlet, you need to install a sump pump.

Buy one large and strong enough to get water to the farthest irrigation point (pumps are rated for discharge in gallons per minute or hour, and for "head" the height they can lift water). Add a check valve between the pump and the first irrigation point to prevent water backup.

The systems shown on these two pages collect water from main plumbing lines. To do this, pipes must be accessible from a crawl space or basement.

How do you get water to the garden?

Health officials believe that the safest way to apply gray water is below the soil surface or under 4 inches of mulch through drip irrigation, perforated pipe, or leach field. Below-surface applications eliminate human contact, and the soil can filter out harmful organisms.

You can run water directly from the source into the distribution system (although you shouldn't apply gray water while it's hot). But most users collect the water in containers first; this gives them more control over distribution. To prevent buildup of residue in tanks and distribution systems, it's best to filter gray water at the inlet to the tank.

If you're using drip irrigation, filtering is critical to prevent emitters from clogging. Place a filter on the tank inlet (see top right photograph on page 172), and use a 200-mesh drip-irrigation filter at the outlet (you'll also need a backflow preventer and pressure regulator).

Clean filters as often as necessary to keep water flowing through them (they clog faster when you wash muddy clothes or linty towels). To clean fabric-type filters, let them dry, turn inside out to remove the sediment, then flush with water. No matter bow well the water is filtered, storage tanks need cleaning periodically. To clean them, flush with fresh water. If heavy winter rains come this season, shut off gray-water systems so the rain can leach sediments from the soil.

(Figures omitted)
COPYRIGHT 1990 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Publication:Sunset
Date:Jul 1, 1990
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