How do I go about rerouting my pipes so the greywater from my shower and sink can be used to flush the toilet?

Asked by Richie
Anchorage, AK


David Edwards PhD

Answered by David Edwards PhD

Santa Clara, CA

EarthBound Homes

June 1, 2010

That depends on the type of toilet you have -- but more importantly, is this really the best way to use greywater?

  • The problem with greywater is that it is not just water, but is also filled with many other things like lint, hair, soap, skin cells, dirt, and anything you wash off your body (and your clothes, if you use the clothes-washer water as well).
  • Most plants like all this stuff, as it provides nutrients that decompose into the soil.

The problem with using it in your toilet is that it tends to gum up the mechanisms that make the toilet function.  If you have a pressure-assisted toilet, there are multiple problems:

  • first, using greywater on a pressure-assisted toilet invalidates the warranty;
  • secondly, the water must be pressurized by a pump in order for the pressure-assisted toilets to function properly, meaning the pump would have to maintain that pressure 24/7 (not typical of sump pumps that are most commonly used to pump greywater because they have a certain tolerance for the greywater debris I talked about earlier); and lastly,
  • greywater cannot be stored for more than 24 hours without being purified or it turns into blackwater, which is raw sewage.

There are some commercial systems that do this, like the BRAC systems, but these require a significant amount of energy for the pumps and use potable water to backflush the filters on a weekly basis.

Maybe sending water outside in Anchorage isn't such a good idea in the dead of winter, making something like the BRAC system worth the cost ($1,800 plus installation), but down here in California, it just doesn't make economic sense.


For more information:

You should also read Jesse Terzi's Ask A Pro Q&A, "We want to design a greywater system for the campground we're renovating. Can you help?"

Tagged In: greywater

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