An accessory dwelling unit (ADU) needs its own drains, water supply and hot water, and in Lakewood, ADUs start with planning review before building permits. The biggest plumbing questions are how the ADU's drains reach the sewer, whether the existing water service and sewer lateral can handle the added load, and where the water heater goes.
*This guide is general planning information. We list ADU plumbing as a specialty service that hasn't been confirmed yet for referral, so call to ask whether help is available for your project.*
Start with the city
The City of Lakewood home improvements guide lists accessory dwelling units and additions among projects that start with planning review. Plumbing, sewer and mechanical work then go through Building and Safety, per the permits page. Talk to the city early. The ADU's location affects every plumbing decision.
Sewer connection
The ADU's drains usually tie into the main house's sewer lateral, or in some cases get a new lateral. On Lakewood's flat lots, getting enough slope from a rear ADU to the street main can be tight. A sewer camera inspection of the existing lateral shows whether it's in good enough shape to take more flow. An original 1950s lateral with roots or cracks may need repair first.
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Call (708) 350-9399Water supply
The ADU's water typically branches from the existing service line. If that line is old galvanized pipe, or the meter is small, pressure may suffer when both units use water. Consider water line replacement as part of the project. Ask your water provider whether a meter upgrade or separate meter applies. In Lakewood that's either the city or Golden State Water.
Hot water
Options include a separate tank or tankless heater for the ADU, or sharing a larger heater. A separate heater keeps hot water reliable and simplifies billing. See tankless water heaters and water heater replacement.
Gas lines
If the ADU will have gas appliances, the gas piping and meter capacity have to be evaluated. Gas line work is another specialty service; ask when you call.
Budget and schedule
Plumbing is a significant part of ADU cost, especially trenching for sewer and water lines. Get the existing lateral and service line evaluated before finalizing plans. Our sewer line repair cost guide and repiping cost guide show published ranges for related work.
Local context
Lakewood's post-war lots, from the Mutuals to Carson Park near Monte Verde Park, are regular in shape, which helps planning. Rear-yard ADUs often mean longer drain runs. See plumbing permits in Lakewood for more on permits.
When should you call a plumber about this?
Call when you see active leaks, water damage, sewage, repeated clogs, low pressure across the house, or anything involving gas. Call too when a job needs a permit, or when you're buying a home and want an inspection before you close. Describe what you've noticed, the home's age and your address or cross streets. You'll hear on the call whether your address and job are covered.
How was this guide researched?
This guide was written for Lakewood, California homeowners and checked against the sources below on November 11, 2026. Rules and prices change, so confirm anything important with the agency or provider. See our editorial policy.