Yes, in Ohio for landscape irrigation only. Diverts laundry/shower water from septic. Reduces tank load 30-40%. Permits required from the county health department; costs $1,500-$5,000 to retrofit.
More detail
Gray water in Ohio code includes only water from clothes washers, showers, bathroom sinks, and (sometimes) bathtubs. Kitchen-sink water is excluded because of fat-and-grease load. Toilet water is always classified as black water and must go to the septic. A gray-water diversion system uses dedicated drain lines from approved fixtures to a surge tank, then to a subsurface irrigation field (drip irrigation lines under landscape areas) or to an approved gray-water treatment unit. Permits and inspections are required by the county health department; some counties (Hamilton, Warren) have established review protocols and others handle them case-by-case. Retrofit cost depends on existing plumbing access and irrigation field design; $1,500-$5,000 typical. Septic load reduction is meaningful (30-40% lower wastewater volume to the tank) and extends pumping cadence proportionally. Good fit for homes with large landscaping irrigation needs. Cincinnati gray-water permit reality: Hamilton County and Warren County have established gray-water-permit review protocols; Clermont and Butler County handle them case-by-case. Permit review takes 2-6 weeks. The biggest factor in retrofit cost is whether the existing plumbing makes it easy to separate gray-water sources from black-water sources without major demolition. Most pre-1990 Cincinnati homes have plumbing routes that complicate retrofit; new construction is a much cheaper time to design in gray-water capability.