It's an unsettling color to see pouring into a white tub, and the good news is that the most common cause is also the least serious. But "usually harmless" isn't a diagnosis. Where the brown comes from matters, and there's a two-minute test that sorts it out before you spend anything.
Fill a clear glass from the cold tap and let it sit a moment. Then fill a second glass from the hot tap. Compare them against a white sink or a sheet of paper.
Only the hot water is brown: the source is inside your house, and almost always inside the water heater tank. Work through the fixes below.
Both are brown: the heater is innocent. Something upstream is feeding you rusty water — the city may have flushed water mains or opened a hydrant on your street, a water main may have had a pressure event, or, on a well, the filter may have failed or iron levels shifted. Run the cold tap for a few minutes; city-side events usually clear within a few hours. If cold water is still brown the next day, call the water utility (or test the well) rather than your plumber.
| What You See | Likely Cause | First Move |
|---|---|---|
| Hot only, worst after the house sat empty | Sediment stirred up in the tank | Run the hot taps; flush the tank if it persists |
| Hot only, getting worse over months | Anode rod used up, tank starting to rust | Check the anode rod; plan around the tank's age |
| Both hot and cold, started suddenly | City main work or hydrant flushing | Run cold taps; wait a few hours; call the utility if it lasts |
| Both, plus grit or a metallic taste, on a well | Well iron or a failed filter | Check the filter; consider a water test |
| Hot only, one bathroom | Rusting galvanized pipe on that run | Note it; it's a pipe-aging issue, not the heater |
Sediment. Minerals in the supply settle to the bottom of the tank year after year. Normally they sit there quietly, but a tank that went unused on vacation, or got drained partway, or suddenly works harder, stirs the layer up and serves it to your faucets. This is the classic vacation-homecoming brown water, and it often clears on its own within a day of normal use.
A spent anode rod. Inside the tank hangs a metal rod designed to corrode so the tank doesn't. When it's finally consumed — typically after several years — the tank's steel becomes the thing that corrodes, and rust starts tinting the hot water. This is what an anode rod does and why catching it worn-out-but-not-finished actually saves tanks: a rod that's still partially there can be replaced; a tank that's rusting from the inside cannot be un-rusted.
Old galvanized pipes. If the brown shows in one part of the house, or clears after the water runs a minute, suspect the pipes on that run. Galvanized steel rusts from the inside with age, and the first water of the morning carries the night's rust with it.
Brown water that arrives with a sulfur, rotten-egg smell is a related but different problem — bacteria reacting inside the tank — and it's covered in the guide to why a water heater smells like rotten eggs.
Run the hot taps. Open two or three hot faucets, including a tub, and let them run for about 10 minutes. Light sediment often flushes straight through, and if the water runs clear and stays clear, you're done.
Flush the tank. If color lingers, drain several gallons — or the whole tank — through the drain valve with a hose to a floor drain or outside. This is the full procedure in how to drain a water heater, and it's the same flush that should happen yearly anyway. Set the heater to Off or Pilot first, and give the water time to cool before you drain much of it.
Check the anode rod's age. If the heater is five or more years old and the rod has never been looked at, assume it's spent. Replacing it on a tank that still flushes clear afterward can add years of life. On a tank well past ten years, weigh the rod's cost against simply planning a replacement.
Watch for the comeback. Brown water that returns within a few weeks of a thorough flush is the tank telling you its lining is gone. At that point, flushing is buying weeks, not years — start budgeting for a new heater rather than repeating the flush.
Ordering a new water heater on day one. Sediment is the most common cause of brown hot water, and a flush costs an hour. Replace the tank when the flush stops working, not before you've tried it.
Panicking — or shrugging. Rusty-looking water from iron and sediment is generally more ugly than dangerous, and people shower in it without incident. But "generally" isn't "always": if you're on a well and the color change came with a taste or odor change, get the water tested instead of guessing. The shrug is also wrong when the brown keeps returning — that's a tank on its way out.
Run the glass test first: cold brown means call the utility or check the well; hot-only brown means your tank needs a flush, and possibly an anode rod. Most cases end at the flush. The ones that don't are the tank quietly announcing its retirement — better to hear it now than from a leak.
Usually, yes. The common causes — iron, rust, and tank sediment — are aesthetic problems more than health ones, and showering or washing hands in discolored water is generally fine. Hold off on drinking it and on doing laundry until it clears, and if you're on well water and the change came with a new taste or smell, get a water test to be sure.
Because the tank sat still. Water standing in the heater for days or weeks lets sediment and a little corrosion product build up undisturbed, and the first heavy use stirs all of it into the supply at once. It typically clears within a day of normal use; if it doesn't, flush the tank.
That points away from the heater — if the tank were the source, every hot tap in the house would run brown. A single bathroom usually means the pipe feeding it, often older galvanized steel, is rusting internally. It tends to be worst in the first water of the morning, after the pipe has sat full all night.
Typically a few hours once the work is done. Run the cold taps for several minutes to pull clear water into the house, then avoid running the hot water until the cold runs clear — otherwise you'll draw the rusty water into your tank and stretch the problem out. If it's still discolored the following day, call the utility.
If sediment was the cause, a thorough flush plus yearly flushing usually keeps the water clear. If the cause is a consumed anode rod or a rusting tank, flushing helps briefly and the color returns — that's the signal to replace the rod (on a younger tank) or start planning on a new heater (on an old one).