As more and more homes and businesses are built in the Central Texas area, the supply of water is a huge concern of mine. The lakes and aquifers can only sustain us so long without extensive conservation. As water becomes more scarce, it will become more expensive. So what can we do? Or should the question be - what water can be re-used or recycled in a household?
Utility and environmental regulators have agreed on a few principles to follow. First, "black water" is that water from a household that is so dirty it should not be considered for re-use. This is water from the toilets, of course, but it's also water used to wash dishes, rinse food, and all the other stuff we do in the kitchen. Why is this black water? Because this water contains a lot of organic matter, bacteria, concentrated detergent residues, and oil and grease - stuff that does not break down quickly, get diluted, or otherwise behave well in a "water re-use" operation.
"Gray water" is all the other water we use in the household that goes down a drain. Bath and shower water is gray water; yes, it has some soap, some shampoo, maybe a little bit of organic stuff. But this water can be filtered in a fairly simple process and be quite clean, in that re-use sense. The same is true for water used in bathroom sinks, for hand-washing, for tooth-brushing. It's true for water from the washing machine - but bear in mind that some regulators object to that water if you're washing baby diapers.
A typical family uses around 200 to 300 gallons of water a day in the house. That does not include watering the lawn or gardens, washing the vehicle with the hose, or letting the kids run through the sprinklers in the summer. It's for all those daily operations we do: cooking; bathing and hygiene; using the restrooms, doing the laundry. Of this total water usage, the black water really makes up only a quarter at most. If a person decides to plumb a new home to drain gray water to a separate container and treatment system, that's a lot of water volume that can be recaptured, and then put to other uses. Some systems are built to use this treated gray water (again, simple filtering may be all the treatment it gets) to irrigate the lawn and garden. Some even use this water for flushing the toilets, cutting down on the amount of "drinking water" that is needed in the household. So gray-water capture and recycling can offer some big advantages.
If you do build a system to capture and re-use gray water, make sure your plumber follows codes. For instance, gray-water piping is specified to be a different color than the drinking water piping. Sometimes the two pipes are specified as different diameters, too. You don't want any cross-connections, obviously. You also don't want any possibility of "back-flow" of the gray water into a drinking water line. These are simple problems to avoid, if you have a good design installed by a good contractor.
Water recycling makes sense for a lot of properties. And water is getting more expensive all the time. Check out gray-water re-use.