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Gray Water Systems: Good Idea or Bad Mistake?

Gray Water Systems: Good Idea or Bad Mistake?

By Carl Seville, Networx

Most of us realize that water is a scarce resource and are looking for ways to use less of it in our homes. We need water to drink, for cooking, cleaning, flushing toilets, and (unless we are into xeriscaping) irrigation.  We can save water by using more efficient fixtures, taking shorter showers, fixing leaks, and being more careful about how we use it.  We can reuse water by capturing both rainwater, and gray water – the stuff that goes down the drains in our bathroom sinks, showers, tubs, and washing machines.

It is possible to clean and filter gray water and then reuse it, both inside our homes and for irrigation, but it takes effort to do it right and it comes with challenges.  First, we need to distinguish gray water from black water, which is the waste from kitchen sinks, dishwashers, and toilets.  Black water can’t be reused in our homes until it is fully treated and sanitized in a sewage treatment plant, something that most of us don’t have in our backyards. Gray water is easier to prepare for reuse, most commonly in indoor storage tanks designed just for this purpose.

Installing a gray water system in your house requires two sets of drain lines, one for the gray water and one for the black water. All the black water goes into the sewer or septic tank, and rest goes into the gray water tank.  This tank, usually in the basement or crawlspace, filters, treats and stores the gray water until it is reused. Filters take out the big yucky stuff – hair, lint, etc.

Treatment is necessary to keep the water from getting toxic, and is done with chlorine, ultraviolet light, or a combination of these and other methods.  Treated gray water can be used to flush toilets and for irrigation, under certain conditions.  If you want to use it to flush toilets, you need to have supply lines to each toilet that are separate from the regular water in the house – easy if you’re building a new house, more work on an existing home.  Gray water can be used for underground or soaker hoses, but it shouldn’t be used to supply sprinkler heads because it can spray nasty stuff in the air, in a process referred to as “aerosolizing,” that you could breathe in and make you sick.

If you decide to put a gray water system in your house, make sure you understand exactly how much maintenance it needs, and what chemicals or other treatment the water needs.  If you’re not the kind of person who likes to take care of things, think hard before you give it a try.  Filters can get clogged, pumps can break, chemicals can go out of balance – there are lots of complicated things that can go wrong with a gray water system.

Although they are allowed in many places (for instance, Arizona laws make it fairly easy for Phoenix plumbers to install gray water systems), many plumbing professionals are not big fans of gray water systems because of the maintenance and health issues involved in using them.  If you want simple, safe ways to save water, install high efficiency fixtures, take shorter showers, don’t run water unnecessarily, and put in drought resistant plants. If you want to collect water, stick a few rain barrels on your downspouts.  They are cheaper, will collect a lot of water, and you can use it for irrigation and even flushing toilets if you want, without the complicated treatment gray water requires.


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2:16PM PST on Nov 4, 2014

Live long and prosper

2:18PM PST on Jan 28, 2013

I live in an area where we only have septic systems, which are delicate indeed. Graywater helps prolong the life of the septic, and I have it coming into areas of the property where normally I would have sprinklers. A win-win situation!

6:46PM PDT on Aug 22, 2012

Now that the last of my brood of 7 has moved out, I find I barely use water at all. I collect rain water for the garden to drink.

12:17PM PDT on Aug 5, 2012

Lauren W, Using the wash water is not a problem, but if your type of detergent is a type that will to be utilized directing by the plants, all the better. Other wise, many detergents must be broken down before offering themselves as a nutrient.

9:12AM PDT on Aug 4, 2012

I enjoyed reading the comments. I too have been watering the veggie garden and a few flowers during this drought with washtub water. My plants respond beautifully to this. Seems like it should be a little easier to collect grey water than proposed in article.

10:05AM PDT on Aug 2, 2012

I haven't heard of it termed "black water" before, but of course it makes sense to have different pipes. I collect the cold water that comes out before my shower runs hot and use that to fill the toilet tank, which is convenient enough, but otherwise I still believe in homeowners and businesses using greywater.

5:43PM PDT on Jul 31, 2012

Thank you

4:09PM PDT on Jul 31, 2012

I don't know about this but it sounds kind of one sided to me. I don't know that you need chemicals for graywater. I use the water from my bath and kitchen to water my garden and so far have seen no negative effects. It is not a huge amount of water saved but in this drought we are experiencing every little bit helps. I would like to find out more.

4:07PM PDT on Jul 31, 2012


6:35AM PDT on Jul 31, 2012


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Disclaimer: The views expressed above are solely those of the author and may not reflect those of
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people are talking

Thank You for sharing:)

Thanks Dr. Greger for sharing this very interesting article and the many informative links.


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