Greywater Systems

By Greg Richardson

Greywater is a term used to describe any water that has been lightly tainted but does not contain sewage. Conventional sources of household greywater include the water disposed of in sinks, showers, and washing machines. Although you wouldn’t want to drink greywater, it can be reused for other household needs, like irrigating plants and flushing toilets, which means that each unit of water can be used twice rather than just once. 

To reuse greywater, it is necessary to set up a greywater system. Such systems can be integrated into a new or existing home’s plumbing system and are often distinguished by whether or not they purify the greywater before reuse.

Greywater Systems – With No Purification

Many greywater systems do not treat greywater before reuse and, as a result, are generally simpler to construct and maintain. These systems can be so straightforward that using a hose or pipe to redirect greywater into a barrel or bucket can be sufficient. The website greywaterguerillas.com has a small archive of case studies on “do-it-yourself” greywater systems of varying complexity.

Another way to use greywater — without purifying it — is by using it to flush toilets. Sink-to-toilet greywater systems are already available in the U.S. and are commonplace in Japan. Two of our favorite models include the AQUS System and SinkPositive (see below).

Greywater Systems – With Purification

Systems that purify greywater are generally safer but require more equipment and maintenance. Additionally, because these systems are also more complex, they generally require professional assistance to install. To make the process of putting together such a system easier, prefabricated greywater systems are available. Here are some examples:

•          BRAC Systems
•          The Clivus Greywater System
•          The ReWater® System

 Greywater Laws - IMPORTANT

Greywater policies differ from state to state but are generally very stringent because of environmental and safety concerns. Before installing a greywater system, please check with your local health-code department to learn about regulations governing the use of greywater. Currently, Arizona has the most supportive policy in place, and regulations in Texas, New Mexico, Florida and California are also encouraging of greywater use. 

 General Advice about Greywater Systems

Note that greywater can contain harmful chemicals, bacteria, and viruses that pose a risk to the environment and public health if mishandled. As a general rule, you should not store greywater for over 24 hours, and avoid contact with greywater, especially when using a greywater system with no purification. For these reasons, using underground infiltration pipes and burying drip irrigation lines under mulch are preferred greywater irrigation practices.

In such systems, it becomes especially important to be careful about what you drain down your sink (e.g.: consider switching to “all natural” cleaning products). Also, because of lint and food contamination, laundry water and kitchen greywater are not generally suited to unfiltered reuse in drip or sprinkler irrigation systems.  Finally, make sure to scale your greywater system proportionately to match both the production of greywater in your home as well as your need for it.