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 bathrooms sinks, showers, tubs and washing machines.

It is possible to clean and filter gray water and 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 — 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, which is usually in the basement or crawl space, 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, referred to as "aerosolizing," that you could inhale 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 install 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.

Carl Seville originally wrote this for It is reprinted with permission.