A Plumber in Los Altos, Where Sewer Repairs Add a Valve

Permits and local rules

Three city rules a Los Altos sewer quote has to follow

Section 12.14.020: backwater and relief valves
Los Altos replaces Section 710.1 of the California Plumbing Code with its own text, readopted with the 2025 codes in October 2025. Every new, replaced or repaired building sewer that connects to the city's main must have an accessible, approved backwater valve and an atmospheric relief valve. The relief valve goes upstream of the backwater valve, outside the building close to the foundation, and cleanouts that drain through the valve carry a permanent "backwater valve downstream" label. Where a repair has no cleanout near the foundation, the relief device may sit near the repair instead.
Los Altos Municipal Code, Chapter 12.14 (opens in a new tab)
Who rebuilds the lateral, and who keeps it clear
Owners maintain the entire lateral, from the house to the main, which in Los Altos usually lies in the street. Reconstruction is split: the owner rebuilds from the house to the first joint past the property line, and the city rebuilds from there to the main, as its standard detail SS-8 draws it. Section 10.04.290 makes the city's share subject to the cleanout rule, a cleanout where the building sewer meets the lateral under a box set flush with the ground. The city pays no plumbing bills except when a street lateral needs reconstruction or repair.
City of Los Altos Maintenance Services (opens in a new tab)
Chapter 11.08: protected trees near the trench
A protected tree in Los Altos is any tree 12 inches in diameter at four feet above grade, any native species from 10 inches, any heritage tree and any tree the city required to be kept. Damaging or killing one is unlawful, not only removing it. During construction a preserved tree is fenced no closer to the trunk than its dripline, and the grade around it is kept as it was out to the dripline. A lateral trench across a front yard under an old oak has to be planned around that.
Los Altos Municipal Code, Chapter 11.08 (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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Copper pipe fittings: elbows, a tee, reducers and couplings. Photo: Torsten Bätge, CC BY-SA 3.0, via Wikimedia Commons.

The houses here

Quarter-acre lots on a sewer laid in the 1960s and 1970s

Los Altos grew mostly between 1950 and 1980, and its sewer grew with it. The city's 2017 Sewer System Management Plan says about three quarters of the system went in during the 1960s and 1970s and that more than 90 percent of the pipe is vitrified clay. Houses sit back on lots of a quarter acre or more, so the lateral from the house to the street main is often a long run under lawns, driveways and big trees. The same plan says most stoppages happen in laterals rather than in the city's mains, and that city crews root-foam about a third of the system each year. The city's monthly permit reports also list whole-house demolitions, and every rebuild raises the question of whether the old lateral can serve the new house.

Part by part

When the address changes the plumbing answer

Lots along Adobe, Hale, Permanente and Stevens creeks
The city names four creeks, plus the bypass near Blach School that carries overflow from Permanente Creek to Stevens Creek, and says flooding is most likely on properties closer to them. Its floodplain page links FEMA's guide to protecting building utilities from flood damage, which is worth reading before a water heater or softener is set low in a garage in a mapped flood zone.
Homes outside the city line on the city sewer
Los Altos also collects sewage from unincorporated county land in its sphere of influence, a small part of Mountain View and part of the Town of Los Altos Hills. Los Altos Hills is a separate town with its own rules and building department, so an address there that drains into this system is not covered by the Los Altos permit rules on this page.

The work

The plumbing work Los Altos rules shape most

Replacing a sewer line, valves included
No one may work on a lateral or building sewer in Los Altos without a written permit from the city, and the city's plumbing code adds its own requirement on top: a new, replaced or repaired building sewer gets an accessible backwater valve, with an atmospheric relief valve upstream of it outside the house near the foundation. The Building Division's handout asks for both to sit in a Christy box or yard box, with the cleanout labeled "Backwater Valve Downstream." The city's August 2026 permit report shows the rule at work, with sewer replacements marked "Backwater valve required."
Reusing the old sewer for a rebuilt house
Under Section 10.04.240 of the municipal code, an old building sewer may serve a new building only after the city's superintendent has examined and tested it and found it meets city requirements. New building sewers and laterals are tested by filling them with water in the superintendent's presence, and the contractor supplies the plugs, water and labor. The code also sets a 4-inch minimum for a building sewer at a slope of at least 1.25 percent, which takes planning on a deep lot where the house sits far back from the street.
One sewer for a house and a back building
Big lots invite a second building, and the city's code lets one owner's buildings share a single side sewer while the property stays in that ownership. If part of the lot is later split off and sold, the portion that is not directly connected must get its own connection to the public sewer, and neighboring buildings fronting the same street may never share one. A plumber laying out a line to a backyard structure should know at the start whether a lot split is part of the plan.
Water heaters and the remodel reach code
Los Altos amended the 2025 Energy Code with electric-readiness rules for single-family remodels. If wall framing is removed or replaced within three feet of a gas water heater, the project must leave a space at least 2.5 by 2.5 feet and seven feet tall for a future heat pump water heater, with a condensate drain that flows by gravity or an outlet for a condensate pump. Where circuits nearby are added or altered under an electrical permit, a 240-volt-ready circuit or pathway goes in too.
Gas lines to pools, fire pits and outdoor kitchens
Quarter-acre lots leave room for pools, spas and outdoor kitchens, and the same reach code covers them. Adding or extending a gas line to a pool or spa heater, a sauna, a fireplace, an outdoor cooking appliance or an outdoor heater also means conduit or wiring for a future electric equivalent, a receptacle or junction box within five feet, a reserved breaker and a marked space on the drawings. The city's plumbing code separately calls for an earthquake-actuated gas shutoff valve at or near the meter whenever a meter is reinstalled or relocated.

Before you hire

Five things to settle before the trench opens

Does the quote include the backwater valve, the upstream relief valve and a cleanout labeled "Backwater Valve Downstream," as Section 12.14.020 requires?
If the break is under the street, has anyone asked the city whether its share of the reconstruction applies before you pay for that section?
Will the contractor arrange the city's water test of the new line and set the cleanout box flush with the ground?
With an oak or other protected tree near the route, how will the trench stay clear of roots inside the dripline?
Check the C-36 Plumbing license at cslb.ca.gov and ask for proof of workers' compensation coverage for everyone working in the trench.

Timing

Holiday backups and the city's work hours

The city says sewer backups rise during the holiday season, when wipes, tissues and cooking grease go down the drains. When one happens, city staff check the main sewer line; if it is clear and flowing, the blockage is in the lateral and the owner calls a plumber. Residential construction is allowed from 7 am to 5:30 pm on weekdays and from 9 am to 3 pm on Saturdays, with no work on Sundays or city holidays, and every inspection is booked online through eTRAKiT.

Questions

Sewer, valve and hard water questions from Los Altos owners

Our sewer lateral broke under the street. Does Los Altos pay to fix it?

For the street end, usually yes. The city is responsible for reconstructing the lateral from the main to one pipe segment past the property line, provided the line has the cleanout the code requires; the owner rebuilds the rest. Keeping the whole lateral clear, roots and grease included, stays the owner's job all the way to the main, and the city does not pay plumbing bills except for street-lateral reconstruction or repair.

We are only repairing a cracked section of sewer line. Do we still need a backwater valve?

Yes. The Los Altos amendment covers repaired building sewers as well as new and replaced ones, so a repair permit comes with an accessible backwater valve and an atmospheric relief valve. The code allows one concession for repairs: where there is no existing cleanout at or near the foundation, the relief device may be placed near the repair, upstream of the new backwater valve.

Why does our water heater fill with scale so quickly in Los Altos?

Part of the water is very hard. Cal Water's 2025 report for its Los Altos Suburban system shows its local groundwater ranging from 137 to 440 ppm of hardness, averaging 305, against about 97 for the treated Valley Water it buys, and the report notes hard water can leave mineral buildup in pipes and water heaters. It also cautions that some softeners add salt that causes problems at wastewater treatment plants.

Can we still replace our gas water heater with another gas one?

The city's own permit records say yes for now: its August 2026 issued-permit report includes a 50-gallon gas water heater replaced in a closet, next to several heat pump installations. The local reach code adds conditions only when the job goes further, such as removing wall framing within three feet of the heater or altering nearby circuits under an electrical permit.

Who supplies our water, Cal Water or the city?

Cal Water, through its Los Altos Suburban District, which has served the area since 1931 and also reaches parts of Los Altos Hills, Cupertino, Mountain View and Sunnyvale. It mixes local groundwater with treated surface water bought from Valley Water, and the city's own water-saving page points residents to Cal Water's rebates. Cal Water reports no known lead service lines in its systems; the pipe past the meter belongs to the house.

Keep exploring

More on plumbing work and Los Altos

Other trades in Los Altos

Guides and smaller jobs

Where this page belongs

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.

Clay laterals, a city valve rule and hard well water: Los Altos plumbing

Three city rules a Los Altos sewer quote has to follow

Section 12.14.020: backwater and relief valves

Who rebuilds the lateral, and who keeps it clear

Chapter 11.08: protected trees near the trench

Get quotes for plumbing work in Los Altos

Quarter-acre lots on a sewer laid in the 1960s and 1970s

When the address changes the plumbing answer

Lots along Adobe, Hale, Permanente and Stevens creeks

Homes outside the city line on the city sewer

The plumbing work Los Altos rules shape most

Replacing a sewer line, valves included

Reusing the old sewer for a rebuilt house

One sewer for a house and a back building

Water heaters and the remodel reach code

Gas lines to pools, fire pits and outdoor kitchens