June 5, 2008
Greywater — which is all household wastewater except for toilet water — can profitably be reused for irrigation. But by “re-circulate,” I assume that indoor reuse is what you are asking about, and that’s not always the best idea. In order to reuse waste water for flushing toilets, for instance, you would need a multi-stage filter, holding tank and some kind of pump. All-in-all, that’s an expensive project.
Reusing greywater for flushing toilets, while an excellent practice on a large scale, rarely holds up to life cycle analysis when practiced on a residential scale, since so much hardware, electricity, chemicals and maintenance are used to save so little water.
There’s a more thorough analysis of this issue, the preferred practices and exceptions in our compendium of common greywater errors, and more on indoor greywater reuse here.
The more common reuse of household waste water from showers, sinks and washing machines is for outdoor irrigation of trees and bushes. You’ll find complete information in our book Create an Oasis with Greywater, and information on simple systems free, on our Web site.