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Tales from a Plant Addict

Fun (& a few serious) facts, tips and tricks for every gardener, new and old.

Grey Water Use in the Home Landscape

The drought has made gardening a challenge this summer, to put it mildly. As we anxiously watch weather radar in hopes of a few drops of rain, the question of what to do if it doesn't rain weighs heavily on our minds as the days and months go by. The extended drought has made a lot of us realize how much we take our water supply for granted.

This week Decatur was forced to implement the most drastic water restrictions in the city's history. The restrictions include prohibiting any irrigation of landscape plantings other than vegetable gardens. As a result, many gardeners have called our Master Gardener Help Desk with questions on the safety of using grey water for irrigation.

Grey water is defined as "wash water" and includes water used in bathtubs, showers, washing machines, or kitchen sinks and dishwashers. It does not include water flushed down toilets–this water is considered to be "black water" and is not safe for reuse as is. About 65% of water used in households is grey water.

During a drought when water is in short supply, recycling grey water for irrigation seems to be a no-brainer, right? The idea of using grey water seems simple enough, but there are several factors to consider before you start using it in your landscape.

The safety of grey water is questionable for both you and your plants. By definition, grey water is considered to be contaminated water. Its usual destination is the sewer and the water treatment plant.

Grey water will contain any or all of the following: bacteria, food particles, dead skin, hair, oil, grease, soap and other detergents. Some of the bacteria in grey water are harmful, and may create a risk for human health. For this reason, homeowners should NOT use grey water on edible crops, particularly root and leaf crops which may directly contact the water, even if they will not be eaten raw.

Some soaps and detergents contain sodium, boron, and chlorine, which have potential for building up in the soil and causing problems with plants either by direct toxicity or by altering the soil pH which can affect plant growth. The University of Massachusetts advises homeowners to use no more than one half gallon of grey water per square foot of garden per week to avoid problems with salt buildup in the soil. They also advise alternating use of grey water with fresh water to help flush salt buildup from the soil. Since Decatur has prohibited all use of fresh water outdoors on landscape plants other than vegetables during the current restrictions, this alternating schedule is not possible. Irrigating with grey water in Decatur's current situation makes plant problems related to salt buildup more likely.

If you are contemplating using grey water in your landscape, here are a few more tips to consider:

  • Apply grey water directly to soil, never directly to plants
  • Use grey water within 24 hours of collection. Storing grey water for longer periods encourages bacterial growth which will create foul odors and/or a health risk to you.
  • Do NOT use grey water on edible crops, particularly leafy and root crops which may directly contact the water, even if they will not be eaten raw
  • The most "desirable" grey water to use is from the shower and/or bathtub, followed by the bathroom sink, utility sink, washing machine, kitchen sink and dishwasher. Kitchen sources are ranked last because of the concentrations of food particles, grease and other undesirable contaminants they may contain. Automatic dishwashers use detergents that are particularly harsh and unhealthy for your landscape, so use of this grey water is the worst choice among grey water sources.
  • Choose plant-based soaps and detergents without added phosphates, boron, or chlorine.
  • Avoid grey water containing liquid fabric softeners, as these products tend to be very high in sodium.
  • Do not use grey water that was used to wash dirty diapers, oily- or gasoline-soaked rags.
  • Grey water is typically alkaline due to soaps and detergents. Avoid using grey water on acid loving plants like evergreens and azaleas.
  • Use grey water only on established plants, not seedlings or young plants
  • Mulch applied in areas where grey water is used will speed decomposition of many contaminants in the water
  • Keep mulch away from the base of the plant since hot wet conditions will promote disease development

Keep in mind that actually collecting grey water can be a challenge. In many cases, grey water use is a temporary measure to weather a drought. Typically, homeowners collect grey water in buckets or use a small pump to distribute the water.

In chronically drought-stricken areas, some homeowners use alternative plumbing that redirects grey water to landscape use. This type of permanent solution is much more complicated, as it involves local plumbing codes and health department inspections. This is an idea in its infancy in Illinois. Just this summer, the Doyle family of Oak Park began a home addition project that will be the first single-family home grey water system in Illinois. The system is considered illegal under Illinois Plumbing Codes, but a variance was granted to the family after a long discussion process.

If you are subject to the water restrictions in Decatur and are interested in using grey water to irrigate your landscape plants, the City of Decatur has requested that you call the Water Service Division at (217) 875-5705 to discuss your plans.

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