How to Use Gray Water for Gardening


Household gray water is any used water that does not come out of a toilet. For example, the water that drains out of a washing machine after doing laundry is considered gray water. It is called gray because it is no longer fit for human consumption, however, is not harmful to the environment. While most gray water flows down the drain into the sewer, you can save it and use it to water the garden.

Things You'll Need

  • Tape measure
  • Bucket
  • Rain barrel
  • Garden hose
  • Calculate the safe amount of gray water to use in your garden by measuring the length and width of the space with a tape measure. Multiple the width by the length to reach the square footage. Divide the total square footage by half to arrive at the number of gallons of gray water to use per week.

  • Collect water in buckets from inside the home including any bathwater and excess water that flows out of faucets when washing hands or brushing teeth. To collect washing machine water, insert the end of the machine's drain hose into the top of a large container, such as an unused rain barrel.

  • Apply the gray water to any grass and ornamental plants using the amount determined to be safe based on the square footage. You can pour the buckets directly into the soil, or attach a garden hose to the faucet on the bottom of the barrel and run the hose to the desired location. Apply the gray water first, and if additional water is needed apply fresh water from a garden hose.

  • Test the pH level in your soil once every one to two weeks to ensure that sodium is not building up in harmful levels. Insert the metal rod of a soil pH tester into the ground and read the digital display or locate the number at the end of the pointer. The proper pH is below 7.5. If the pH begins to increase, stop using the gray water.

Tips & Warnings

  • If you use washing machine gray water, switch to a laundry detergent that does not claim to "soften" clothing and avoid using fabric softener. You should also switch to chlorine-free bleaching solutions.
  • You can also have a professional install a household piping system that stores the gray water in a storage tank.
  • Do not use washing machine water if you launder cloth baby diapers, since the water is contaminated with fecal matter.
  • Do not use water from the kitchen sink or dishwasher that was used to wash dishes, since there are too many food particles.
  • Do not use gray water on small seedlings or on acid-loving plants.

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