Greywater and Septic Systems

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Greywater systems

Greywater systems recycle “gray water” from sinks, showers, and washing machines for use in irrigation or landscaping. These eco friendly systems can save hundreds or thousands of gallons of water per year. However, water that has come into contact with human waste, from the toilet or from washing cloth diapers, is considered “black water” and cannot be routed through a greywater system. Usually, the legal code regulating grey water systems specifically prohibits discharging cloth diaper laundry through a grey water system because the bacteria poses a health risk.
If your washing machine is hooked up to your greywater system and you want to cloth diaper, you have two options:

  1. You can hand wash cloth diapers using the bucket and plunger method, and dispose of the water in the toilet.
  2. You can install a three way diverter valve on your washing machine. This will allow you to choose whether the water is discharged into the grey water system, or into your sewer/septic system.

If you do choose to install the diverter valve and wash your cloth diapers in your machine, you might consider purchasing a detergent to use specifically for the diaper laundry. Detergents that are safe to use in greywater systems may not be effective at cleaning diapers. See our Detergent Index for more information.

Septic systems

About one-quarter of American households rely on septic systems. Unlike grey water systems, septic systems treat both grey water and black water. In general, if your washing machine drains into a septic system, you don’t need to do anything different with your diaper laundry, beyond normal maintenance of the septic system. Most common detergents such as Tide are labeled as being septic-safe. Some people with septic systems prefer to use plant based detergents, but this is a personal choice. Some sources recommend using liquid detergent for conventional septic systems and powdered detergent for aerated septic systems, but we were not able to find any clear research showing this is necessary.

According to most researchers, using normal amounts of bleach for household cleaning purposes is fine with septic systems. For example, from Cornell University’s Cooperative Extension:

More than 2 gallons of hypochlorite bleach or 5 gallons of pine cleaner would be needed to kill most of the bacteria in a 1,000- gallon septic tank. It would then take 45-60 hours for the bacterial populations to recover from a lethal dose of hypochlorite bleach, and 30-65 hours to recover from a lethal dose of pine cleaner.

Under normal conditions of household use, the majority (97 percent to 99 percent) of sodium hypochlorite reacts with soils, stains, and organic solids in the wastewater to form salts and other harmful compounds.

The remaining 1 percent to 3 percent of sodium hypochlorite entering a septic tank forms chlorinated compounds. Current research shows that the majority (87 percent to 94 percent) of these chlorinated compounds are degraded or removed by septic systems. As a result, the formation of chlorinated compounds from the normal use of hypochlorite bleach is not considered a threat to human health or the environment.