What are California's water conservation requirements for ADU fixtures?

California enforces some of the strictest plumbing-fixture flow limits in the country through CALGreen (the California Green Building Standards Code, Title 24 Part 11). Every new residential fixture in an ADU must meet these maximum flow rates, and they are verified through plan check and inspection — not optional best practices.

Maximum fixture flow rates

Note that older 1.6 gpf toilets are no longer compliant with current California code, even though they are still sold elsewhere. If you reuse a fixture salvaged from a remodel or buy out of state, check the engraved flush rating before installing it. The same caution applies to showerheads and faucets, which are stamped with their GPM rating either on the body or in the packaging — the figure printed there must match what your fixture schedule promises.

Why California pushes the limits this hard

These rules exist because California is chronically water-stressed and adds tens of thousands of new dwelling units every year. An ADU is a brand-new household drawing on the same constrained supply, so the state treats every new fixture as an opportunity to lock in permanent savings. The cumulative effect is significant: a CALGreen-compliant ADU bathroom uses a fraction of the water a 1990s bathroom did, which is exactly why these limits are written into mandatory code rather than left to homeowner preference.

How compliance is documented and verified

• On the plans: the plumbing fixture schedule must list each fixture's make/model and rated flow so the plan checker can confirm compliance at a glance.
• At inspection: inspectors may verify installed fixtures match the approved schedule, and some flag non-compliant showerheads or faucets at final.
• For showers with multiple heads: CALGreen generally limits the combined flow, so a rain head plus a body-spray array can quietly violate the rule even if each individual head is rated 1.8 GPM.

Why it matters for your budget and rebates

Low-flow fixtures aren't just a code hurdle. They reduce the demand load on your water service, which can be the difference between tying into your existing meter and paying for a costly service upgrade. Many California water districts also offer rebates for high-efficiency toilets and smart irrigation that you can stack onto an ADU project.

Flow-rate enforcement and local amendments vary by jurisdiction. Some water-stressed districts adopt stricter limits — confirm with your local building department and water utility.

Our plumbing plan sets specify CALGreen-compliant fixtures throughout and document the flow rates in the schedule. If you also need energy compliance, our Title 24 reports (a $240 add-on) coordinate water-heating efficiency with the rest of your MEP package.