Brown water from the faucet: causes and fixes, San Diego

Brown water from a faucet almost always traces back to one of three places: your water heater, your home’s own supply pipes, or the city main outside, and the pattern of which taps are affected tells you which one.

It’s an unsettling thing to turn on a tap and get rust-colored water instead of clear. The good news is that the fix almost always starts with a simple test you can do yourself: run the hot and the cold separately and see which one is actually the problem. That one detail narrows it down fast.

The fastest way to diagnose it: hot, cold, or both

Before anything else, isolate the source with this test. Run the cold tap alone for a minute, then run the hot tap alone for a minute, and pay attention to which one is discolored.

What you see	Most likely source	What it means
Hot water brown, cold water clear	Water heater tank	Sediment or rust built up in the tank, stirred loose by hot water flow
Cold water brown, hot water clear	Home’s cold supply line	A corroding pipe, often aging galvanized steel, on your side of the meter
Both hot and cold brown at once	City main or municipal system	Main flushing, nearby repair work, or a break stirring up sediment
Brown water that clears after a few minutes of running	City-side event	Temporary; should resolve without any repair
Brown water that keeps returning over days or weeks	Internal pipe corrosion	Needs inspection, likely pipe replacement rather than a one-time fix

That one test does most of the diagnostic work. Everything below fills in the details for whichever pattern you’re seeing.

Hot water only: it’s almost always the water heater

Every tank-style water heater collects sediment, minerals, and rust flakes at the bottom over years of use. San Diego’s hard water accelerates this, since the same minerals that scale up shower heads and coat fixtures also settle inside the tank. When the heater has sat idle, or when demand pulls water hard through the tank, that settled material gets stirred into the outflow and shows up brown or rusty at the tap.

A tank flush often clears this. If brown hot water comes back quickly after a flush, or if it’s accompanied by a metallic smell or the water heater itself is more than 10 to 12 years old, the tank’s interior lining may be breaking down, which is a sign the unit is nearing the end of its life rather than something more sediment removal will fix.

Cold water only: look at the supply pipe

If cold water runs brown while hot water stays clear, the sediment theory doesn’t hold, since cold water never passes through the tank. This points instead to corrosion happening inside the cold supply pipe itself, either within your home or in the line running from the street to your meter.

In San Diego, this is most common in homes still running original galvanized steel supply lines, which corrode from the inside out over decades and shed rust into the water flow, especially right after a period of low use or a pressure change. Our galvanized pipe replacement guide covers how to tell if that’s what you’re dealing with and what replacing it involves.

Both hot and cold: check with the city first

When brown water shows up everywhere at once, hot and cold, every fixture, the cause is usually outside your house entirely. San Diego Public Utilities periodically flushes water mains to clear out accumulated sediment, and nearby construction, a hydrant use, or a water main break can do the same thing by stirring up rust and mineral deposits inside the municipal pipe network.

A quick way to confirm: ask a neighbor if they’re seeing the same thing, or check the City of San Diego’s water service alerts for flushing or repair notices in your area. This kind of event typically clears within a few hours to a day once the system settles and you run your cold taps for a few minutes to flush your own lines.

Is it safe to drink or use?

Don’t drink it or cook with it while it’s visibly brown. The EPA classifies iron, which is what causes most of this discoloration, as a secondary contaminant, meaning the concern is mostly aesthetic rather than acutely toxic at typical levels. Sediment itself isn’t inherently hazardous either, but it’s unpleasant and can carry bacteria.

The bigger concern isn’t the rust color itself. It’s what the rust indicates. In homes with older pipe, especially anything installed before the 1980s, ongoing internal corrosion can also mean the pipe is leaching other things you can’t see. Until you know the cause and the water runs clear again, skip drinking it, skip cooking with it, and hold off on running the dishwasher or a laundry load, since agitating sediment through appliances can clog valves and filters.

What to do right now

1. Run a cold tap for a few minutes, ideally the lowest fixture in the house or an outdoor spigot, before doing anything else.
2. Test hot and cold separately to identify the pattern using the table above.
3. Check with neighbors or the city if both hot and cold are affected, since that usually means it isn’t your plumbing.
4. Avoid the water heater, dishwasher, and laundry until you’ve identified the source or the water runs clear.
5. Note how long it’s been going on. A one-time event that clears fast is very different from something that keeps coming back.

When to call a plumber

Call if any of these apply:

• Cold water brown repeatedly over several days, especially with visible galvanized pipe in the home
• Hot water brown even after a full tank flush
• Discoloration paired with a metallic taste, rusty smell, or reduced water pressure
• A home built before the 1960s that’s never had its supply lines inspected

If it turns out the cause is an aging supply line rather than a one-time city event, that’s usually a pipe replacement conversation, not a repeat-flush conversation. For a broader look at what hidden pipe problems tend to look like before they become obvious, see our guide on signs of a hidden water leak, and our San Diego hard water guide covers how local water chemistry contributes to both scaling and pipe corrosion over time.

Get a real answer, not a guess

Brown water is unsettling, but it’s almost always traceable once you know which pattern you’re looking at. If flushing the tank and running the taps doesn’t clear it, or if it’s clearly your own supply line and not the city, Plumbing Pro San Diego can diagnose it on-site and tell you exactly what’s causing it. Call (858) 400-4417, or visit our pipe repair page to see how we handle corroding supply lines across San Diego County.