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Grey Water: What is it and how to use it

By Paul Rodman (paulgrowAugust 29, 2012

Grey water is water from your sinks, showers, tubs, and washing machines. I also include evaporate from your air conditioner or humidifier in this category. Learn how to retain and use it in the yard and garden.

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Reusing greywater as a water conservation practice can be as elaborate as you want to get or as simple as catching your air conditioner water in a bucket. Greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products. While greywater may look "dirty," it is a safe and even beneficial source of irrigation water in a yard. There are many simple, economical ways to reuse greywater in the landscape.  Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system.

Greywater is different from fresh water and requires different guidelines to be used.

  1. Don't store greywater for more than 24 hours. If you store greywater, the nutrients in it will start to break down, creating bad odors. Adding two tablespoons of chlorine bleach per gallon of water will extend storage time somewhat.
  2. Minimize contact with greywater, because it can potentially contain pathogens if even trace amounts of feces get into the water. Your system should be designed for the water to soak into the ground and not be available for people or animals to drink.
  3. Infiltrate greywater into the ground, don't allow it to pool up or run off (knowing how well or poorly water drains into your soil (or the soil percolation rate of your soil) will help with proper design. Pooling greywater can provide mosquito breeding grounds, as well as a place for human contact with greywater.
  4. Keep your system as simple as possible, avoid filters that need upkeep. Simple systems last longer, require less maintenance, require less energy and cost less money.
  5. Match the amount of greywater your plants will receive with their irrigation needs.

6. Root crops which are eaten uncooked should not be irrigated with greywater.
7. Plants that thrive only in acid soil should not be watered with greywater, which is alkaline.
8. Use greywater only on well-established plants; not seedlings or young plants
9. Disperse greywater over a large area, and rotate with fresh water to avoid buildup of sodium salts.

Capturing Greywater

Those of us who have forced air furnaces with central air conditioners will have a drain line that usually runs to a laundry tub or floor drain. This is water that has condensed when the hot air flows over the evaporator coils. This is clean water and can be drained into a bucket or other container for use on plants. You can install an overflow hose to carry away the excess water when the container has filled.

Your washer is another fairly easy to use source for greywater. The drain hose can be routed into a holding barrel which contains a pump. As the barrel fills the water is pumped outdoors into your holding tank.


A more elaborate system involves having a plumber come in and separate the toilet drains in the house from the other drains that would come from the sinks, washing machines etc. in the home. The toilet sewage would continue to drain into the sewer or septic system. The remaining greywater would be usually routed outdoors into a holding tank for use in the yard or garden.

Greywater irrigation may not be a good choice if:

  • your soil is not suitable - If your soil is either too permeable or not permeable enough, you may not be able to recycle your greywater, or you may need a system with some modifications.
  • your area too small - You need enough soil to process the greywater and enough plants to use it.
  • your climate unsuitable - If it's too wet to benefit from irrigating with greywater, there may be a better way to dispose of it. If it's too cold, you will only be able to recycle in the warmer months. In cold climates, the heat in greywater may be more valuable than the water itself.
  • there is a low cost/benefit ratio - Where legal requirements dictate a complex system and there is only a small flow of water, greywater recycling is not economically feasible.
  • it is inconvenient - If the greywater system you are considering is more expensive and requires more maintenance than a properly functioning septic or sewer system.
As you can see there are pros and cons as to the use of greywater as well as some expense if you want to set up a more elaborate system. My personal opinion after researching this practice is that I don't think I would want to use greywater on food crops but can see where it would have benefits on the lawn or flower beds.

Only you can be the judge on if and how you would want to use it.

  About Paul Rodman  
Paul RodmanPaul Rodman has been gardening for over 45 years. He is an Advanced Master Gardener, and American Rose Society Consulting Rosarian. He is President Emertius of the Western Wayne County Master Gardener Association in Wayne County, Michigan. He currently serves as the greenhouse chairman of this group. Rodman has amassed over 5500 volunteer hours in the Master Gardener program. Rodman is the garden columnist for The News Herald newspaper, in Southgate, Michigan. He has also written for the Organic web site. He is a certified Master Canner and has taught classes on Home Food Preserving for 7 years. He has lectured on various gardening topics throughout southeastern Michigan. His favorite pastime is teaching children about gardening. For the past several years he has conducted classes for second grade students teaching them about subjects ranging from vermi-composting to propagation.

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