As an eco-minded earthling who recycles and composts, I was baffled when I heard the words “gray water” mentioned the other day. What was gray water, I wondered?

It turns out that the word is greywater, and it’s simply water that’s being recycled. Also called sullage, it’s the water left over when you do dishes, wash your laundry, or take a bath.

We really don’t think of reusing this water, but it makes sense to do so. Why waste so much water, after all, when it’s still perfectly useable? No, we can’t actually cook with it, and I definitely wouldn’t bathe in my dishwater, but I wouldn’t mind watering our plants outside with it.

Some places regulate the use of greywater—which is named after its appearance and should not be confused with “black water,” or waste water containing fecal matter and urine. Believing that it may be harmful, depending on what is used in it, many cities do not allow citizens to reuse their water. However, if you’re already using eco-friendly cleaners, soaps and personal care products, what could the harm be?

In many places of the world where water is scarce, the use of greywater is very common and unregulated.

Using greywater is definitely more eco-friendly than sending it off to sewage treatment plants and then into our rivers and streams; that said, the concerns about the various chemicals and germs in it from its contact with humans and food are legitimate ones. While there has yet to be a case of humans being harmed through the use of greywater, it’s not documented enough to be fully measured.

There are greywater recycling systems to use that may eliminated these concerns, but many people who use greywater do so manually—that is, by transporting the water directly from the home with buckets. Such greywater can be used for:

• Flushing Toilets: By using bathwater or shower water to flush a toilet, a house could cut its water use by 30%.
• Irrigation: Using greywater that has not been in contact with harsh cleaners to water plants can be an effective way of saving water otherwise spent doing so.
• Living in Extreme Conditions: The Mars Desert Research Station actually uses graywater for its daily operations! Greywater has also been used to create ice rinks.

Would you, or do you, use greywater? Why or why not? Share in the comments section below.