Using Gray Water in Your Landscape and Garden

Source(s): Kim D. Coder, Professor of Community Forestry, Warnell School of Forestry and Natural Resources, The University of Georgia

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During times of water shortage, slightly used gray water can provide an alternative landscape irrigation source. Separating slightly used (gray) water from sewage (black water) makes good conservation sense.

Daily, homeowners misuse or waste an average of 33 percent of 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.

Gray water is water that can be used twice. It 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. NOTE: 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.
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.

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.

Tips for using gray water:

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

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Resource(s):

Make Every Drop Count

Xeriscape: Seven Steps to a Water-Wise Landscape

Center Publication Number: 253