Plumbing Redwood City

Where Redwood City's water, sewer and purple-pipe lines meet a plumber's work

Redwood City runs its own water utility, buying Hetch Hetchy water from San Francisco and moving it through 28 pressure zones, and it runs a recycled water system from Redwood Shores to the Bayfront. Both shape plumbing here: a backflow assembly is tested every year by a tester on the city's list, and a building on recycled water needs a shutdown cross-connection test whenever its plumbing changes. The sewer lateral splits at the property line, and the cleanout is the owner's.

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Redwood City's City Hall
Redwood City's City Hall. Photo: King of Hearts, CC BY-SA 4.0, via Wikimedia Commons.
Water supplier
City of Redwood City, buying from the SFPUC's Hetch Hetchy system
Pressure zones
28, through about 259 miles of city pipeline
Sewage treatment
Silicon Valley Clean Water, a joint powers authority
Recycled water
Pumping since 2007, from Redwood Shores to the Bayfront

Permits and local rules

Local rules a Redwood City plumbing bid should account for

  1. Backflow tests by the city's qualified testers

    Redwood City accepts backflow test results only from testers on its Qualified Tester List, and a tester needs CA-NV AWWA backflow tester certification and a Redwood City business license to get on it. Test reports are due within 30 days of the city's first notice. City Code Chapter 38 requires an assembly to be tested when it is installed, repaired or relocated and at least once a year after that, and every well and backflow assembly in the city is tested or inspected annually.

    City of Redwood City Public Works (opens in a new tab)

  2. The Recycled Water Use Ordinance

    Adopted in July 2008 and now City Code Chapter 38, Article VIII, the ordinance sets the recycled water service area and lists which uses are required and which are voluntary. Its use table marks single-family homes as discouraged or prohibited users, while single-family HOAs are encouraged to consider recycled water for their landscapes. Recycled water must never be plumbed into a household's domestic system.

    City of Redwood City Public Works (opens in a new tab)

  3. Who owns the lateral, and the cleanout

    The lower lateral, from the property line to the sewer main, is maintained by the city; the upper lateral is the owner's, and the city counts everything inside the property line as private, cleanout included. Repairing a lateral requires a permit. The city suggests owners consider a backflow device to protect against sewage backing into the house, and depending on the address, the sewer bill comes from the city or from San Mateo County.

    City of Redwood City Public Works (opens in a new tab)

  4. Which plumbing work is exempt from a permit

    The city's handout requires a permit to install, alter, repair, remove or replace any plumbing or gas system, and exempts only narrow work: stopping leaks, clearing stoppages and removing and reinstalling toilets. Once a concealed pipe has to be removed and replaced, a permit is required. In an emergency the work may go ahead, but the permit application is due the next working business day.

    City of Redwood City Building Division (opens in a new tab)

State license for this work: C-36 Plumbing, C-42 Sanitation System. Look up a contractor's license on the CSLB website (opens in a new tab).

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Free to request, and you agree the scope and price with the person you hire before work starts. In California, a job over $1,000 in labor and materials, or one that needs a building permit, must be done by a contractor licensed by the CSLB in the right class. Ask for the license number and check it at cslb.ca.gov.

Copper pipe fittings: elbows, a tee, reducers and couplings
Copper pipe fittings: elbows, a tee, reducers and couplings. Photo: Torsten Bätge, CC BY-SA 3.0, via Wikimedia Commons.

The houses here

Pre-1980 houses, a filled bay shore and hills once on septic

Redwood City's 2025 water plan puts about 70 percent of the city's housing before 1980 and notes that homes built after 1990 are the ones more likely to have compliant fixtures. The city's fixture handout follows from that: on a building finaled before January 1, 1994, a permitted job ends with non-compliant toilets, faucets and showerheads replaced before final. The city is also split by ground. Much of Redwood Shores sits below high-tide level behind a ring of levees, and its owners association counts 3,173 single-family homes in 26 local HOAs, while the houses of Emerald Lake Hills relied on septic tanks until a sewer system went in during 1982.

Part by part

Two corners of Redwood City with their own plumbing story

  • Redwood Shores

    Levees ring the peninsula because the ground sits below high tide, and in April 2020 FEMA told the city that without levee changes the Shores would be mapped as a flood hazard area, covering about 4,700 households. Sewage here flows straight to the Silicon Valley Clean Water plant. The Building Division recommends submitting plans the owners' association has already approved.

  • Emerald Lake Hills

    Redwood City's water service area takes in this unincorporated hillside, but its sewers belong to the Emerald Lake Heights Sewer Maintenance District, which San Mateo County Public Works runs for the Board of Supervisors. The district's flow then passes through Redwood City's own pipes, so check the bill to see which agency a lateral question goes to.

The work

Calls a Redwood City plumber gets that other cities rarely see

  1. Plumbing changes in a building on recycled water

    The recycled water system serves more than 450 connections, Oracle, Electronic Arts and HOAs among them, for landscape irrigation and for toilet and urinal flushing in dual-plumbed buildings. Its rules require a full shutdown cross-connection test before occupancy, every four years, and any time the onsite drinking-water or recycled-water plumbing changes, so even a remodel in a dual-plumbed condo can bring one. Recycled lines are purple and labeled, and hose bibs are not allowed on them; quick couplers approved for recycled water take their place.

  2. Water heaters to the city's handout

    Redwood City requires a plumbing permit to install, remove, replace, raise, lower or relocate a water heater, and wants it in hand before work starts. Its handout calls for seismic straps in the upper and lower thirds of the tank, and for an expansion tank on any system with a check valve, backflow preventer or pressure regulator, adding the words no exceptions. A house with a backflow assembly at the meter is exactly that kind of system.

  3. Turning gas back on after a long shutoff

    Water here is the city's, but gas is PG&E's. The city's gas pipe testing handout explains that once a meter has been disconnected for more than six months, PG&E requires a pressure test before it will reset or reconnect the meter, and a plumbing permit is required. The test holds at least 10 pounds of pressure for no less than 15 minutes, on piping already covered, and the applicant supplies the gauge.

  4. A cleanout at the property line

    The city's sewer pages give the owner the upper lateral, from the house to the property line, and say it is the owner's job to install a cleanout; the city maintains the lower lateral out to the main. Where a household has a cleanout at the property line, Redwood City offers to snake the line from that cleanout to the main. Lateral repairs need a permit from the Engineering and Construction Division rather than the Building Division.

Before you hire

Questions to settle with a plumber in Redwood City

  • For a backflow test, is the tester on Redwood City's Qualified Tester List with a city business license?
  • In a dual-plumbed building, who arranges the recycled water shutdown test that a change to your plumbing triggers?
  • If the gas has been off more than six months, does the bid include the permit and the pressure test PG&E needs?
  • Will a new cleanout go at the property line, where the city's snaking service can reach the main from it?
  • Is the license a C-36 Plumbing classification you have checked at cslb.ca.gov, and will the permit go through eTRAKiT under it?

Questions

Redwood City pipe questions, from the Shores to the hills

Can we water our own yard in Redwood Shores with the purple-pipe recycled water?

Generally not. The city's recycled water use table marks single-family homes as discouraged or prohibited users, while single-family HOAs are encouraged to consider it for common landscaping. Recycled water must never be connected to a home's drinking-water plumbing, and recycled systems may not have hose bibs. Ask your HOA how its landscape lines are separated from household water.

We are selling our Redwood City house. Does backflow come up?

It can. City Code section 38.43 requires the seller to disclose whether backflow preventers are required to be installed on the property, and premises with an auxiliary water supply, such as a well, or internal cross connections need an assembly that is tested every year. If you have one, have the latest passing test report ready for the buyer.

Who clears a sewer backup in Redwood City, the city or our plumber?

Both, depending on where it is. The city maintains the lower lateral from the property line to the main and offers to snake that run from a cleanout at the property line. The upper lateral and the cleanout are yours, so a blockage between the house and the property line, or a house with no cleanout, is a plumber's job, and lateral repairs need a permit.

What does Redwood City want before a new dishwasher goes in?

Its kitchen, bath and laundry remodel handout requires dishwashers to drain through an approved air gap device set above the flood level rim of the sink, citing the California Plumbing Code. The same handout caps newly installed kitchen faucets at 1.8 gallons per minute, so a remodel that changes both should plan for the air gap at the sink.

Does a laundry-to-landscape graywater system need a permit here?

Not if it takes one washing machine and discharges less than 250 gallons a day. The city's graywater handout follows the state plumbing code on that point. Any other graywater system needs a permit, drawings and specifications, and a percolation and mantle test. BAWSCA, which runs the Peninsula's regional rebate programs, does not run a regional graywater program.

Where these facts come from

Checked against these public sources in October 2026. Rules and programs change: confirm permit requirements with the city before work starts, and a contractor's license on the CSLB website.

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