Saving Water in Southern Homes - Recycling Gray Water

Saving Water in Southern Homes – Recycling Gray Water

Saving water is an important part of the Green movement, so I decided to explore how to save water in homes – particularly in southern homes.  Let’s look at recycling gray (or grey) water to reduce demand.

Gray water is the water used in baths, showers, washing machines and hand sinks, and it accounts for about 40% of indoor water use.  It gets its name from its cloudy appearance – it’s not drinkable (“white water”), but it doesn’t carry human waste (“black water” or sewage).  Normally gray water is combined with sewage and treated together, but it can also be collected separately and recycled in the home.  Here’s a diagram of how a gray water system works, courtesy of BetterBuildingsOregon.org.  Please note that gray water should never be used for drinking or cooking, but it can be used for lawn or garden irrigation or for filling toilets.

There are a few things to consider with gray water systems.  First, gray water often contain contaminants like nutrients and food particles.  Plants use these contaminants for growth, but some contaminants (like salt or soap residue) can harm plants.  You should avoid using non-natural soaps if you are recycling your gray water.  Also, bacteria can grow from these contaminants, so gray water should be used within 24 hours or purified.  Since gray water is often discharged hot, it should be stored before use.  And any place where gray water can be accessed should be labeled “Gray Water in Use” so people know not to drink it.

I have designed one new home with a gray water system.  We collected from one plumbing stack that served 2 showers, 2 lavatories and the washing machine, and we combined the storage with a rainwater cistern (check with your Health Department – some locations don’t allow this) and used the water for irrigation only.  It did help keep the cistern full during periods of light rainfall.

My experience is that gray water systems in homes aren’t always practical – especially when retrofitting an existing home.  It requires a separate drain system inside the house that’s parallel to the sewage path.  If gray water is used to fill toilets, a second supply system is needed that must be fully separated from the drinking water, and a pump is required to maintain pressure.  Still gray water recycling is a way to save a significant amount of water, and as fresh water becomes more precious and more costly we’ll probably see it in more southern homes.