In times of water shortage, slightly used water can provide an alternative landscape irrigation source for your residential customers.

Separating slightly used (gray) water from sewage (black water) makes good conservation sense. Drinkable water becomes more valuable every year. Some communities restrict water use periodically, curtailing outdoor watering first when shortages occur. This can be disastrous for businesses that depend on irrigation to establish or maintain landscapes.

One water-conserving alternative that merits a closer look is gray water. Daily, homeowners misuse or waste an average of 33 percent of our valuable drinking water. Most of this water misuse is for diluting toilet, sink and laundry wastes and from slightly used sink, shower and laundry water. Every day we use many gallons of drinkable water for purposes like landscape irrigation, which could employ gray water.

WHAT IS GRAY WATER?

Gray water is water that can be used twice. Gray water includes the discharge from kitchen sinks and dishwashers (NOT garbage disposals); bathtubs, showers and lavatories (NOT toilets); and the household laundry (NOT diaper water). Using gray water can almost double home water-use efficiency and provide a water source for landscape irrigation.

Unfortunately, many health regulations consider any non-drinkable water as black water or sewage. Many plumbing and health codes do not accept gray water for reuse because of assumed health risks. For the legal status of gray water in your community, county and state, consult your local building codes, health officials, sanitation engineers and pollution control officials.

With proper foresight, lobbying and marketing to allow gray-water use in landscapes, plant losses can be minimized in times of water shortages.

WHY USE GRAY WATER?

Gray water separation and use could save 25 to 40 percent of drinkable water for consumption. Community-wide gray water use could allow a reduction in the size of water-purification and sewage-treatment facilities.

Across the nation, landscape watering and toilet flushing are the major home uses of drinkable water. The most effective uses of gray water are for flushing toilets and watering landscapes. Imagine the water conservation benefits nationwide from using gray water for just these two purposes!

GRAY WATER CONTENT

Gray-water composition depends on the water source, plumbing system, living habits and personal hygiene of the users. The characteristics of gray water will be influenced by:

Cleaning products used, Dishwashing patterns, Laundering practices, Bathing habits, and Disposing of household chemicals.

The physical, chemical and biological characteristics of gray water and when it is used varies greatly among families and businesses.

See the accompanying table for an average make-up of gray water. Notice that, at normal concentrations, few materials in gray water will damage trees and shrubs if they are applied to the soil. Also, few detrimental soil changes will occur from properly managed gray-water applications.

Gray water has several unique characteristics:

It contains high levels of grease. Use a grease trap, and do not pour grease, oils or fats down the drain.

It is warmer--by 10 to 15 degrees-- than normal wastewaters.

It contains a large amount of fibers and particles. Filters must remove these materials before gray water enters an irrigation system.

SUBSTANCES TO AVOID

You should not allow some materials and water inputs to enter the gray-water collection system:

Cleaners, thinners, solvents and drain openers should bypass the collection system. Avoid using cleaning and laundry materials that contain boron.

Do not use artificially softened water. Softeners replace calcium and magnesium with sodium. Long-term irrigation with high-sodium water can cause soil problems.

Do not recycle drainage water from swimming pools. It contains large salt concentrations and stabilized chlorine and/or bromine that will cause problems for landscape plants.

HEALTH CONCERNS

Properly treated and continuously monitored gray water can be a valuable and safe resource for landscape irrigation. However, ignoring problems and not checking the system periodically can lead to human health and maintenance difficulties. Misused gray water can spread typhoid fever, dysentery, hepatitis and other bacterial and viral problems.

Disinfection is critical for gray water held more than 3 hours. Health hazards--especially with eye contact-- are present in dissolved and suspended organic material and detergents.

To make it easy to identify and to prevent usage mistakes, add a vegetable dye to gray water. In a new installation or in a plumbing retrofit, use colored pipe to identify the lines carrying gray water.

COLLECTING AND HOLDING

There are two principal ways of collecting and holding gray water commercially:

1. Pipe it from selected drains into an aboveground, usually in-house, holding tank. This system uses gravity to move the gray water into the tank and a pump to remove it.

The gray-water tank should be durable and non-corrodible. (Never use containers for holding tanks that once held corrosive chemicals, organic solvents or pesticides. Even minute traces of these chemicals might kill landscape plants). Holding tanks of this type will require an attached disinfection unit.

Tank size depends on available space and the amount of gray water produced. If gray-water supplies are inadequate, potable water may be required to supplement the system. Be sure to install one-way valves to prevent contaminating drinkable water with gray water.

Beware of potential backflow or siphoning problems. Install an overflow line with a one-way valve to allow excess gray water to flow into the sewer.

Tank placement is important for gravity feed, maintenance and aesthetic reasons. Because of warm temperatures and high humidity levels around the tank, a sealable cover and good air circulation are critical. Elevated humidities in a wood-frame house, for example, can lead to many structural and aesthetic problems.

Also consider safety factors. Design systems to prevent child and pet injury and/or entrapment.

2. Install a "septic" tank. Whether you are hooked into a city sewer or a private leach field for your black water, you can use a separate in-ground tank for gray water in many places. A gray-water septic tank can be designed to use seepage lines that are dug into the root areas of valuable landscape plants. No disinfection is required--only a coarse filter and grease trap.

In-ground gray-water septic tanks can provide low-maintenance gray water for use in the landscape. Like a black-water septic tank, a gray-water septic tank must meet all health codes. Seek installation advice from sanitation engineers, and do not pump untreated gray water from such septic tanks onto the landscape.

FILTERATION AND DISINFECTION

Disinfecting and filtering gray water removes solids, prevents odors, controls turbidity and foaming, and eliminates health hazards.

Before you can use gray water on the landscape, it must be filtered to remove particulate, fiber and floating materials. A grease trap is critical to prevent filter plugging.

Gray water held more than 3 hours must be disinfected because it contains more harmful bacteria than sewage does. A chlorine concentration of 0.5 ppm will disinfect gray water. As gray water is held overnight or longer, the chlorine slowly moves out of solution. The chlorine in laundry wastewater is too dilute to disinfect a gray-water holding tank.

Tablet or liquid solutions of chlorine, ultraviolet light or heat can disinfect gray water. Chlorine is most commonly used. To ensure proper disinfection, use a dosing pump to measure chlorine input for every unit of water volume.

APPLICATION METHODS

Correctly filtered and disinfected gray water can be applied through normal irrigation systems. Apply gray water at or slightly below the soil surface. Avoid sprinkling or making it into an aerosol. Surface broadcasting by soaker hose is acceptable, providing standing puddles and runoff do not occur. Leach fields from gray-water septic systems also can be used for distribution.

Gray-water surface runoff can cause serious erosion and disruption of surface-water chemistry. Avoid concentrated watering near wells and significant groundwater recharge areas because that can lead to groundwater pollution. It is important to carefully monitor application and infiltration races.

EFFECTS ON SOIL

Gray water has few long-term effects on soil. Gray water slightly modifies soil-organism populations and usually initiates no additional pest problems. Changes that do occur are due to the additional water present. Over-watering and extended periods of soil saturation with gray water can cause severe root problems for plants.

Household levels of bleaches and detergents do not cause problems when gray water is applied to medium and fine-textured native soils. However, when applied to coarse sandy soils with little organic matter, root damage can occur.

Organic matter and soil-texture adjustments are critical in raised beds with gray-water irrigation. Do not use gray water on plants with limited root areas or for hydroponics.

TREES AND SHRUBS

Gray water has few detrimental effects on trees and shrubs growing in native soils. Acid-loving plants, however, can have problems because detergents make water more alkaline. Gray-water use for landscape trees and shrubs is shown in the table "Average characteristics of gray water compared with total wastewater."

Gray-water use conserves one of our most precious resources. If managed properly, gray water creates few detriments and many benefits.

CRITERIA FOR USING GRAY WATER FOR TREES AND SHRUBS

• Make trees and shrubs high-priority watering items because of their individual value.
• Use gray water when natural precipitation and normal irrigation water are not available.
• Apply gray water to soil. Never spray on foliage, twigs or stems.
• Never soak bark or root-collar area.
• Do not spray edible plant parts or soils where water splash can move gray water onto edible plant parts.
• Do not use on root or leaf crops consumed by people or domestic livestock.
• Do not use on new transplants.
• Do not use on indoor trees or other plants with limited rooting space, in small containers, or plants normally under saturated conditions.
• Always apply gray water at or slightly below the soil surface. Apply over or under mulch, if present.
• Avoid using micro or regular sprinkler heads that can blow gray-water aerosols downwind.
• Be careful of applications that apply gray water directly to leaf surfaces of ground covers and turfgrasses.
• Control gray-water application and infiltration to prevent standing puddles and surface runoff.
• Test soil periodically to reveal salt and boron toxicity problems.

With populations and land-use demands increasing and high quality water resources continuing to decrease, more water shortages and water use restrictions as well as higher prices will occur in the future. By using gray water the slightly used water from sinks, tubs and laundry--landscape irrigation can be maintained despite outdoor watering bans and higher water costs. However, gray-water use requires changing many health and plumbing codes to accept proper gray-water management in a landscape.