# Why is rusty water coming from my faucet?

> Rusty or brown water from the faucet: how to tell if it comes from the street, the water heater or galvanized pipe, and what fixes each source.

URL: https://hilltoprepipesanfrancisco.com/guide/rusty-water-from-pipes/

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Brown water has three usual sources: the utility's mains, the water heater and old galvanized pipe. Which taps, which side and how long it lasts tell them apart before anyone opens a wall.

Last Updated: October 30, 2026

Rusty water usually comes from one of three places: the utility’s mains after work or a break in the street, a water heater rusting inside, or galvanized pipe in the building corroding from within. Which taps run brown, whether it is hot, cold or both, and whether it clears or keeps coming back point to the source before anyone blames the pipe in the walls.

[Hilltop Repipe San Francisco](https://hilltoprepipesanfrancisco.com/) traces water quality complaints to their source and handles the work when the building is the cause, from water heater connections to [galvanized pipe replacement](https://hilltoprepipesanfrancisco.com/galvanized-pipe-replacement/), across San Francisco, Daly City and South San Francisco, with the work carried out by licensed and insured contractors. This guide covers how to find the source yourself and what each finding means.

Key takeaways

- Neighbors with brown water too, after street work, points to the utility, not your pipe.
- Hot side only points to the water heater.
- Brown water after the water sat or was shut off, clearing in a minute or two, is typical of galvanized pipe.
- San Francisco's water is soft, so rust in old pipe here is corrosion, not mineral scale.
- A partial repipe that leaves galvanized upstream can keep sending rust into new pipe.

## Finding the source

Work through these questions in order. Each one takes a minute and rules a source in or out.

1. **Is it only you?** If neighbors have discolored water too, or crews are working on the street, the cause is likely the utility’s mains. Hydrant flushing, a main break or service line work stirs up sediment that settles back out. In San Francisco, SFPUC’s 24-hour line for water emergencies is 3-1-1; in Daly City, the city’s water department; in South San Francisco, Cal Water.
2. **Hot, cold or both?** Run each side separately at the same tap. Hot only points to the water heater. Cold only, or both, points to the pipe or the supply.
3. **Which taps?** Every tap at once points upstream: the service line, the main or the street. One bathroom or one end of the house points to the branch that feeds it.
4. **When?** Brown first thing in the morning, after a weekend away or after the water was shut off, then clearing, is the pattern of rust settling in old pipe and washing out when flow starts.
5. **Does it clear?** Water that clears in a minute or two and stays clear is settled sediment. Water that stays brown, or comes back every day, means the source is active.

The pipe material is the last piece. A magnet sticks to galvanized steel and nothing else in a water system; the [guide to identifying pipe material](https://hilltoprepipesanfrancisco.com/guide/how-to-identify-pipe-material/) walks through the check.

## Brown, yellow and cloudy water

Not every discoloration is rust. Brown, orange or red water, often with fine particles that settle in a glass, is iron from corroding steel: galvanized pipe, a steel water heater tank or old iron mains. A pale yellow or tea-colored tint can be the same iron at a lower level. Cloudy or milky water that clears from the bottom of the glass upward is usually dissolved air, common after work on the pipes, and goes away on its own. Black particles can come from deteriorating rubber in supply hoses or washers. Green or blue staining in sinks points to copper rather than iron.

## The utility side

SFPUC’s water starts out clear and is treated for corrosion control, with a pH of about 9.3. Work on the mains or on service lines can still send sediment into homes for a while. SFPUC has been replacing its galvanized service lines, the pipe from the main to the meter, with copper; the owner’s side, from the meter box to the building, is the owner’s responsibility. Homeowners report rusty water and a pressure drop at a tap after a utility replaced their meter, which is the kind of disturbance that loosens rust in old pipe downstream. If the utility’s work is the trigger and the building’s pipe is sound, the water clears after flushing.

## The water heater

A tank water heater is a steel tank lined with glass and protected by a sacrificial anode rod that corrodes in place of the tank. Once the anode is used up or the lining cracks, the tank rusts from the inside, and only the hot water turns brown. Sediment flushed from the bottom of the tank can also color hot water for a while. A heater that is rusting inside is usually near the end of its life; the [water heater replacement](https://hilltoprepipesanfrancisco.com/water-heater-replacement/) page covers that decision.

## Galvanized pipe

Galvanized steel rusts from the inside once its zinc coating wears through. The rust builds on the pipe wall and narrows the bore, and pieces break loose whenever flow changes suddenly. That is why it shows up after the water sat overnight, after a shutoff or when a second fixture opens. In hard-water cities, mineral scale mixes with the rust. San Francisco’s water is soft, with average hardness of 62 ppm, so what comes out of old galvanized here is mostly the pipe itself. The same corrosion narrows the pipe, so rusty water and falling flow often appear together; the [low water pressure guide](https://hilltoprepipesanfrancisco.com/guide/low-water-pressure/) covers that side.

[South San Francisco](https://hilltoprepipesanfrancisco.com/service-areas/south-san-francisco/) is different: Cal Water blends groundwater with average hardness of 384 ppm into its supply, so scale and sediment are a bigger share of what comes loose there.

## Is it a health problem?

Color alone doesn’t answer that. Rust stains fixtures and laundry, tastes metallic and clogs aerators and valve cartridges. Where the pipe is galvanized, the more important question is lead, because galvanized pipe that once sat downstream of a lead connector can hold lead in its rust. SFPUC tests tap water for lead at $25 per tap, free for owners who received a letter about a galvanized line on their side. In SFPUC’s 2024 tap sampling, the 90th-percentile lead level was 4.9 parts per billion against an action level of 15. The [guide to whether galvanized pipes are safe](https://hilltoprepipesanfrancisco.com/guide/are-galvanized-pipes-safe/) and the [lead pipes in San Francisco guide](https://hilltoprepipesanfrancisco.com/guide/lead-pipes-san-francisco/) cover it.

## What fixes each source

- **Utility work.** Run cold water at the tap nearest the meter until it clears, then the others. Remove and rinse aerators. If it does not clear, call the utility.
- **Water heater.** Flushing helps sediment. A tank rusting inside is replaced, not repaired.
- **Galvanized pipe.** Flushing clears the moment but not the cause. Replacing the pipe ends it. A [whole-house repipe](https://hilltoprepipesanfrancisco.com/whole-house-repiping/) in PEX typically runs $8,500 to $16,000 for one bath, $12,000 to $22,000 for two and $14,500 to $28,000 for three in the San Francisco area, and copper usually costs more.

## Why a partial fix can keep the rust coming

A [partial repipe](https://hilltoprepipesanfrancisco.com/partial-repiping/) replaces some runs and keeps others. If the galvanized that stays is upstream, such as the service line from the meter box or the main across the garage, it keeps shedding rust into the new pipe, and brown water can continue at fixtures that were just replumbed. That is why the boundary between new and old pipe matters, and why a galvanized service line is often replaced with the interior. The [water service line replacement](https://hilltoprepipesanfrancisco.com/water-service-line-replacement/) page covers that line, and the [repipe vs repair guide](https://hilltoprepipesanfrancisco.com/guide/repipe-vs-repair/) covers where to draw the boundary.

After any repipe, the new lines are flushed with aerators off, because rust loosened from old pipe during the work can lodge in valve cartridges.

If the brown water is coming from the building rather than the street, call or send the form, and the walk-through starts at the meter.

## Questions about this guide

### Is rusty tap water safe to drink?

Don't judge it by color either way. Rust-colored water shows corrosion somewhere upstream, and it stains and tastes metallic. If the building has galvanized pipe, the useful fact is a lead test, which SFPUC runs for $25 per tap. Until the source is known, run the cold tap until it clears before drinking or cooking.

### Why is only my hot water rusty?

Usually the water heater. A steel tank whose lining or protective anode has worn out rusts from the inside and colors only the hot side. Galvanized hot lines can also rust faster than cold ones because warm water speeds corrosion. If cold water is clear at the same tap, start with the water heater.

### Why does water run brown after the water was shut off?

Shutting the water off and turning it back on reverses and surges the flow, which breaks loose rust that had settled inside old galvanized pipe. Brown water that clears within a minute or two after a shutoff is typical of galvanized. Running each tap with the aerator removed flushes it out before it lodges in cartridges.

## Related service

### Galvanized pipe replacement

Old threaded steel supply pipe replaced with PEX or copper, with listed transitions, a flush for loosened rust and a city inspection.

Galvanized pipe replacement

## More guides

- Learn [Are galvanized pipes safe for drinking water?](https://hilltoprepipesanfrancisco.com/guide/are-galvanized-pipes-safe/)Galvanized steel is not lead pipe, and San Francisco's tap results are low. The real questions are what the pipe was once connected to, what its rust carries into the water and how much life the steel has left.
- Learn [Why is my water pressure low in San Francisco?](https://hilltoprepipesanfrancisco.com/guide/low-water-pressure/)Low pressure can start at the street, the service line, a valve, a pressure regulator, the pipe inside the walls or the fixture itself. In a city of hills and old galvanized pipe, measuring before blaming is the whole game.
- Learn [How can you tell if you have galvanized pipes?](https://hilltoprepipesanfrancisco.com/guide/how-to-identify-pipe-material/)A flashlight, a magnet and a coin answer most of it. What you find decides which questions matter next, and what shows in the garage is not always what runs inside the walls.
- Learn [Are there lead pipes in San Francisco?](https://hilltoprepipesanfrancisco.com/guide/lead-pipes-san-francisco/)San Francisco's lead story is mostly history and small parts: lead service lines removed decades ago, short lead connectors on old galvanized lines, and household fixtures and solder. What SFPUC reports, and what an owner can check.
- Decision Guide [Repipe vs repair: when is a full repipe worth it?](https://hilltoprepipesanfrancisco.com/guide/repipe-vs-repair/)A repair fixes a defect. A repipe replaces a material that is failing everywhere. The work is telling the two apart, and the evidence is in the pipe, the pattern of leaks and the flow.