Boil Water Notice in California: What It Means, What to Do, and How to Flush Your Plumbing After

Updated 2026-08-30 · Plumber Comparator editorial team

A crew digs up the street, your pressure sags for an hour, and that evening a robocall tells you to boil your water. What comes out of the tap looks completely normal. That is the confusing part of a boil water notice, and it is the point: the risk is invisible, temporary, and the agency usually does not yet know whether anything got in.

Your water agency's own notice takes precedence over any general guidance, including this page. They know what triggered it and what the lab results say. Where their instructions differ from anything below, follow theirs.

Why a notice gets issued: the pressure story

California's State Water Resources Control Board defines four unsafe-water notices in its Unsafe Water Notification Guidance. A Boil Water notice means the suspected problem is microbiological — something heat kills. Do Not Drink, Do Not Use and Do Not Drink / Do Not Boil mean boiling won't help and may make things worse, the case covered in our guide to tap water safety after a wildfire. A notice can follow a confirmed finding — E. coli in a sample, a turbidity exceedance, a treatment failure — but more often it is precautionary, issued after something physical happened to the pipes. The board lists system pressure loss below 5 psi as a trigger: main breaks, pump or plant shutdowns, power outages, tanks emptying, heavy draw during a major fire.

Here is the mechanism, which few notices explain. Pressure is the barrier: in a healthy main, every crack, joint and leak is pushing water outward. When pressure collapses, that barrier inverts. EPA's notification template for a pressure-loss advisory describes backpressure, backsiphonage, or "a net movement of water from outside the pipe to the inside through cracks, breaks, or joints in the distribution system that are common in all water systems." The soil around a buried main is not clean, and a flooded trench is worse.

This is measured, not theoretical. LeChevallier and colleagues, in the Journal of Water and Health in 2003, instrumented real distribution systems, recorded transient low and negative pressures during ordinary operations, and concluded that leaks act as a portal for groundwater to enter treated water (study on Google Scholar). A 2014 review by Ercumen, Gruber and Colford in Environmental Health Perspectives tied breaches of pipe integrity to measurably increased gastrointestinal illness (study on Google Scholar). That is why a pressure event triggers a health notice even though nothing is visible in the glass.

What to do while the notice is in force

CDC's instruction is a full rolling boil for one minute, and — this matters in the Sierra — three minutes above 6,500 feet, because water boils below 212°F up there and needs longer contact time. Let it cool before use. Wording does vary — California's own template says one minute with no altitude clause, one EPA regional template says three minutes flat — so follow the duration printed on the notice you received.

Use boiled or bottled water for drinking, cooking, making ice, brushing teeth, washing fruits and vegetables, preparing infant formula, and your pets' water bowl — CDC notes pets catch the same germs people do. If you cannot boil, California's template offers a bleach fallback: 8 drops (⅛ teaspoon) of unscented household bleach per gallon of clear water, 16 drops if cloudy, left 30 minutes.

Other uses are less restricted than people assume. Per CDC, laundry is safe as usual, and in many cases tap water and soap are fine for handwashing. Bathing and showering are fine for adults provided you do not swallow the water; CDC advises caution with babies and young children and suggests a sponge bath. Dishwashers are generally safe if they have a sanitizing cycle or a final rinse of at least 150°F. By hand, CDC says wash and rinse normally, then soak the dishes at least one minute in warm water with one teaspoon of unscented bleach per gallon, and air dry.

The appliances everyone forgets

CDC is explicit that you should not use water from appliances plumbed into your line, and the refrigerator is the one people miss: throw out all the ice, from trays, dispensers and automatic makers alike. Same for the coffee maker's reservoir, plumbed countertop dispensers, and instant-hot taps. The bigger misconception is filtration. CDC's guidance is blunt — boil your tap water even if you filter it, because most household filters do not remove bacteria or viruses. A carbon block is built for taste and chlorine, not pathogens. Reverse osmosis is a far finer barrier, but CDC does not publish it as a substitute for boiling during an advisory, and you cannot verify a home unit's integrity mid-event — our comparison of reverse osmosis versus whole-house filtration covers what these systems do and do not remove. Treat every filter in the house as out of service until the notice lifts.

After the notice is lifted: the flush sequence

This is the half nobody covers, and there is a reason: no federal or California authority publishes household flushing durations. CDC ships its post-advisory FAQ to utilities with a literal "[X] minutes" placeholder to fill in; EPA says flushing times vary and that "your water system should tell you if, how, and to what extent you need to clean your water service line"; California's cancellation template says nothing about indoor plumbing at all. Every number below is an individual agency's, and they disagree — so here is the pattern they converge on, with the real spread.

1. Take the aerators off first. LADWP tells customers to remove faucet aerators and screens and put filters and softeners in bypass before flushing, so debris leaves the line instead of packing into the screens. After a main break they are routinely full of rust and grit — see our guide to a clogged aerator causing low pressure at one faucet.
2. Flush the cold lines at your highest-flow fixtures. Five minutes per fixture is the common figure (LADWP, Great Lakes Water Authority, WSSC Water's "usually in 5 minutes or less"); San Jose Water says two minutes, or until the water runs cold. Start with outside hose bibs and tubs, and run until clear at a steady temperature. There is no agreed order for working through the house — CDC says top floor down, WSSC says bottom up, LADWP says nearest the service line first.
3. Then the hot side, and the water heater. Agencies disagree most here. Great Lakes Water Authority says run hot water only until it turns cool — a minimum of 15 minutes for a 40-gallon tank, 30 for anything larger — without draining. LADWP says drain the tank to discharge accumulated sediment, then run the hot taps five minutes. If yours filled with suspect or sediment-laden water, draining is the thorough option; our water heater flushing and sediment guide walks the procedure, and a tank left lukewarm through a long outage raises the separate concern in our guide to water heater temperature and Legionella.
4. Replace every filter. CDC's position is that filters collect germs from the water they process and all should be replaced once the advisory lifts — refrigerator cartridges, pitchers, under-sink units, whole-house cartridges, and RO pre-filters and membranes.
5. Deal with the ice maker. Dump the existing ice, then make and discard the next three batches to flush the supply line before letting the bin refill — LADWP, GLWA and WSSC all say three. Wipe the bin with disinfectant. Flush the fridge's water dispenser too: GLWA says a quart, LADWP says five minutes.
6. Run the appliances empty. A dishwasher cycle on the hottest or sanitize setting, a washing machine rinse, and a regeneration cycle on a softener. Per CDC, do not wash clothes while the water is still discolored — wait until it runs clear and put a dark load through first.
7. Clean and reinstall the aerators. Rinse the grit out. GLWA says simply clean and reinstall; LADWP suggests a bleach soak of no more than five minutes, since longer can damage the aerator.

When it becomes a plumbing problem

Everything above is the utility's side of the meter, or a bucket-and-wrench job on yours. A few symptoms afterward are genuinely yours:

• Pressure never comes back house-wide once service is restored — usually a pressure regulator that gave up during the swing, or debris in a valve (water pressure repair costs).
• Discolored water persists at one fixture only after a full flush — that is your pipe or fixture, not the main. Our guide to brown and discolored tap water separates hot-only from cold-line causes. (Water that is merely cloudy is almost always entrained air and clears from the bottom of the glass upward; our guide to cloudy white tap water has the 30-second test.)
• An aerator clogs again a week later — sediment still working loose in your own lines, often aging galvanized pipe the pressure swing disturbed.
• The water heater turns noisy, popping or rumbling, as stirred-up sediment settles onto the tank bottom.
• A leak shows up days later. The surge when service returns can finish off a marginal joint — if your bill jumps or the meter creeps with everything off, get leak detection on it.

Being ready for the next one

Keep a few gallons of bottled water on hand, because notices arrive with no warning and stores empty fast. Know where your main water shutoff valve is and confirm it actually turns. And sign up for your agency's alert list: a 2016 meta-analysis by Vedachalam, Spotte-Smith and Riha in Water Research found effective compliance with boil water advisories runs around 68%, with awareness the weak link during extreme weather (study on Google Scholar). On a private well, your equivalent is our guide to coliform bacteria in well water and shock chlorination.

Get the plumbing side looked at

Homeowners in Sacramento, Fresno and Chico use Plumber Comparator to line up a licensed local plumber when a main break leaves them with lost pressure, a fixture that won't clear, or a water heater full of grit. Describe the job — when the notice was issued, what you have already flushed, which fixture is still misbehaving — and request a free quote.

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