I have designed and am working to get a gray water system permitted in Petaluma, CA.

I have been informed by the City that, even though there are no proposed connections with city potable water, the property must have a reduced pressure backflow prevention device installed (about $1,000 for the client) because of the potential for cross-connection with gray water.

There is no mention of this in the California Plumbing Code that I can see. There is a city code that justifies this requirement, and it seems to be a fairly common city code. This seems to apply to rain water systems as well as gray water.

  1. Has anyone else run into this?
  2. Has anyone found a way of getting around this if they have?
  3. Does anyone with public health expertise think this code should be changed to only require backflow prevention with actual connections to potable water?



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Hi Damien,

Requiring an RP device is very common for systems that are pumped, but from my experience regulators will not require them for a gravity flow system (or a L2L which doesn’t need a permit).

If you’re planning a gravity flow system I can help brainstorm ways to talk to them about why that system doesn’t need an RP, but if your system has a pump in it I think you’ll just have to do it. Their concern is what may happen later on, when you’re gone, and another person alters the system and creates a cross-connection with the nonpotable greywater and potable water. That’s why they want the RP.



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