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Thank you for this site, excellent resource! I believe this question was also posted, but unaddressed under “composting toilet codes”

I am interested in building a net zero home in unincorporated L.A. County. Albeit costly and more complex than necessary, I anticipate being able to get a greywater system permitted and built. Permitting for a composting toilet appears to be a few years away as well.*

I am puzzled with how to address kitchen sink water since CA considers it to be blackwater. Unless code changes in that respect, I’m having trouble finding a viable solution. There is no sewage line nearby and the property size would require a prohibitively expensive alternative septic system. Any insight to a solution?

Thank you!




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You can ask for a variance to use kitchen sink water, or get it permitted under the Alternative Methods and Materials section of the code. Either of these options would require an open minded regulator. In LA County Health Department talk to Carlos Borja. (You could try the same strategy for a composting toilet. See IAPMO’s new Water Efficiency Standard for some guidance on permitting a composting toilet.)

An alternative idea would be to install a blackwater reuse system, like the Sludgehammer type system. Though you won’t technically be “reusing” the water, you can plant near the drip irrigation lines coming from the treated septic effluent and your plants will get the water anyways.

Good luck!

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In Nevada County, CA, we have an exception in the code that states we can skip over having any septic system, as long as Greywater systems are to code, as well as composting toilet.  As stated above, the dilemma in CA is how to treat the kitchen water, which is classified as blackwater.

I’d like to apply for a variance to exclude a septic system for our one bedroom house, but would need to propose a tested, well supported solution for the kitchen water.  Anyone have suggestions for treating kitchen water that are backed up with info/research/data that I can reference in my application?

Also, heard of any success stories in this regard?


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Hi Rita,

There are a handful of states that consider kitchen water greywater, or dark greywater, and allow for its reuse. I would use those examples. I know of many successful, pre-legal kitchen sink systems in CA, but they are not being monitored by any agency or institution.

There are also permitted examples in CA, a few don’t use the sewer at all.  I’m copying a bit of text  from a document below with example systems.


Through exemptions from the state code, innovative projects have legally and successfully installed kitchen sink systems such as:

  • The “Little House” in San Francisco installed a greywater irrigation systems using all graywater sources, including kitchen water .
  • Evergreen Lodge installed a kitchen sink system from the commercial kitchen in a cafe near Yosemite, California.
  • The Campus Center for Appropriate Technology reuses all household graywater (including the kitchen water) in Arcata, California.
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