As concerns about dwindling water reserves spread from the southwest to the rest of the country, water officials are taking another look at water that goes down the drain.

"Greywater" is the waste water produced from baths, showers, and clothes washers (as distinguished from "blackwater" which is the output from toilets, dishwashers and kitchen sinks). Today, many municipalities are realizing that harnessing greywater could bring real results in both water and cost savings. Greywater systems can be tricky to retrofit into existing structures since they require a distinct set of outflow pipes to be separate from blackwater, but it's relatively easy to accomplish in new construction.

Legal greywater systems are usually limited to households of a certain size (those that generate less than 400 gallons per day, for instance) and are usually restricted to underground systems where the water is used to irrigate trees and gardens.

A word of caution: Most commercial bath and cleaning products contain chemicals that can be harmful to plants (and, of course, to humans as well). Even so-called "natural" products can contain harmful ingredients. Households with greywater systems should use only pure, bio-degradable bath and cleaning products, with no bleach, no dyes, no salts, and no chemicals whose names can't be easily pronounced.

Rainwater Systems: Visitors to tropical islands know that the white roofs which adorn many small rural homes serve to collect precious rainwater, which is then used as the domestic water supply. These days, rainwater harvesting — trapping rainwater and storing it for other uses — is gaining popularity in the U.S.  Rainwater systems are often used to augment and dilute domestic greywater.