What is the minimum plumbing required for a legal ADU in California?

To qualify as a legal Accessory Dwelling Unit, California Government Code requires that the unit provide complete independent living facilities — and for plumbing, that means permanent provisions for cooking, bathing, and waste disposal. Miss any one element and the unit is not an ADU under state law.

The minimum plumbing fixture list

For a standard ADU (attached, detached, or a garage conversion), the plumbing scope must include:

• A full kitchen with a sink connected to both the potable water supply and the drain-waste-vent (DWV) system.
• At least one complete bathroom containing a toilet (water closet), a lavatory sink, and a bathtub or shower.
• A water heater sized to serve the unit — commonly a heat-pump, tankless, or standard tank unit (see mechanical plans for water-heating coordination).
• A potable water connection from the meter or an approved sub-meter.
• A connection to an approved waste disposal system — municipal sewer or an approved septic system.

Every one of these fixtures must appear on the plumbing floor plan and fixture schedule, with flow rates and water heater specifications called out so the plan checker can verify code compliance.

How a JADU differs

A Junior ADU (JADU, up to 500 SF created within the walls of the existing house) has a lighter plumbing requirement. A JADU must have an efficiency kitchen with a sink connected to the DWV system, but a separate, private bathroom is not required if the JADU shares access to the primary dwelling's bathroom. That single distinction is one of the biggest reasons homeowners choose a JADU when they want to avoid cutting a slab or extending a sewer lateral.

Why "minimum" is rarely the whole story

Meeting the bare fixture count is only the start. Each fixture triggers downstream design decisions — drain sizing, vent routing, the fixture-unit load on your existing sewer lateral, and CALGreen low-flow compliance. A bathroom group, for example, isn't just a toilet, sink, and shower; it's three traps that each need a vent, a properly sloped branch drain, and hot/cold supply lines sized for simultaneous demand.

Requirements vary by jurisdiction and by your water/sewer district. Always confirm fixture and connection requirements with your local building department before finalizing design.

Our permit-ready ADU plumbing plans document every required fixture, the water supply design, the full DWV layout, and water heater specs so your set passes plan check the first time. See California ADU requirements for the broader picture, or start an order when you are ready.