Brown or yellow tap water is usually caused by disturbed sediment or rust inside pipes, and it’s almost always the pipes, not the water source itself. It’s rarely an immediate health emergency, but you should stop drinking it until you know what you’re dealing with.
What’s Actually Causing the Color
The most common cause is iron or rust. Cast iron and galvanized steel pipes corrode from the inside over time, and when water pressure changes or flow direction shifts, that rust flakes off and turns your water brown or reddish-brown. Yellow is usually the same thing, just lighter.
A few specific triggers:
Disturbed sediment in your water heater. If the discoloration only shows up in the hot tap, your water heater is the likely culprit. Sediment builds up at the bottom of the tank over years and can cloud the water when the heater cycles or when the unit hasn’t been flushed in a while.
Galvanized steel supply pipes. Homes built before the 1970s commonly have galvanized steel pipes, and some homes built into the 1980s do too. These corrode from the inside out, and once they start going, the rust doesn’t stop. You’ll usually see discoloration at multiple fixtures, not just one.
Municipal water disturbance. Your utility supplier sometimes causes temporary discoloration when they flush fire hydrants, do pipe repairs, or change flow patterns in the distribution system. This typically clears up within a few hours and affects the whole neighborhood. If you have neighbors, ask them. Most water utilities post flush schedules on their website.
Private well iron content. If you’re on a well, naturally occurring iron in the groundwater is a common cause. It’s not corrosion, it’s the aquifer. You’ll usually see it every time you run water, not just occasionally.
How to Tell Which Source It Is
Run the cold tap for about 3 to 5 minutes. If the water clears up, the discoloration was sitting in your supply line or at the water main connection, and it may be a utility-side issue. If it stays brown, that’s inside your home.
Switch to just the hot tap. If only hot water is discolored and cold runs clear, your water heater is the source, not the pipes.
Check one fixture versus all fixtures. Discoloration at a single faucet, especially an older one, can mean that faucet’s aerator or supply line is corroded. Discoloration everywhere points to the main line or water heater.
If you’re on well water and this is a new problem, get the water tested. A basic iron test from a state-certified lab is generally affordable. Contact your county health department for local options and current pricing.
What You Can Check First
Running the cold tap for several minutes is fine. You’re not making anything worse, and you’re gathering useful information.
If the problem is limited to a single faucet, the aerator (the small screen at the tip) may be clogged or corroded. That’s worth mentioning to a plumber because it’s a quick check and a cheap fix if that turns out to be the whole story.
Note your water heater’s age and the last time it was serviced. If it’s over 10 years old and you’re seeing sediment signs in the hot water, that’s exactly the context a plumber needs.
Leave supply lines, the water main connection, and the water heater’s internal components to a licensed plumber. Flushing a water heater drain valve sounds straightforward but it’s not something to attempt on an older unit. The valve sometimes won’t reseal after years of sitting unused, and a slow leak on a sediment-filled tank is a worse problem than the one you started with.
When to Drink It, When Not To
Temporary discoloration after a known municipal flush, which clears after running the tap, is generally low risk for healthy adults. Most water utilities would say to let it run and not drink it until it clears.
Persistent discoloration, meaning it doesn’t clear, is something to take seriously. You don’t know what’s in the water until it’s tested. Don’t drink it, don’t use it for cooking.
If you have very young children, elderly family members, or anyone immunocompromised in the house, err on the side of caution and use bottled water until you have an answer.
When to Call a Licensed Plumber
If the water doesn’t clear after 5 to 10 minutes of running, or keeps coming back, stop troubleshooting and call a plumber. Other situations that warrant a call:
- Discoloration at multiple fixtures consistently
- Low water pressure alongside the color change, or a metallic taste or smell
- Galvanized pipes in a house that’s 40 or more years old
- Visible rust around pipe connections in a basement or crawlspace
A licensed plumber can pressure-test the system, inspect visible pipe sections, and tell you whether you’re looking at a localized issue or a repiping situation. Getting that diagnosis costs less than guessing wrong.
In California, verify any plumber’s license at cslb.ca.gov before work starts. For plumbing, you want a C-36 license. That check takes 30 seconds and protects you if anything goes sideways.
One More Thing
If you’re on a well and this is sudden and you live near any construction or agricultural activity, get a full water test, not just iron. Sudden changes in well water appearance can sometimes indicate contamination that has nothing to do with your pipes. That one’s worth ruling out fast.