Rusty or reddish water coming only from the hot tap almost always points to one of two sources: the water heater itself, or the iron pipes carrying hot water through your house. Cold water stays clear because it bypasses the tank entirely. That single clue narrows things down fast.
The Most Likely Cause: Your Anode Rod Is Gone
Every tank water heater, whether it’s a Rheem, Bradford White, A.O. Smith, or similar brand, ships with a sacrificial anode rod. It’s a metal rod, usually magnesium or aluminum, suspended inside the tank. Its job is to corrode so the tank lining doesn’t. When the rod is fully consumed, the steel tank wall starts corroding instead, and that rust ends up in your hot water.
A typical anode rod lasts somewhere between 3 and 10 years depending on water chemistry, usage, and whether it’s been inspected. Soft water and water softeners speed up rod consumption significantly. If your water heater is more than 6 or 7 years old and the rod has never been checked, there’s a reasonable chance it’s spent.
Signs the anode rod is the issue:
- Rust-colored water only from hot taps, not cold
- A rotten-egg sulfur smell alongside the discoloration
- Tank is older than 6 years with no maintenance history
Internal Tank Corrosion
If the anode rod has been gone long enough, the tank itself starts to corrode from the inside. This is more serious. You might also notice the water heater making rumbling or popping sounds (sediment buildup often accompanies corrosion), or find rust stains around the base of the tank.
At that stage, flushing the tank can temporarily improve the water color, but it won’t fix the underlying metal. A tank that’s corroding internally is typically near the end of its life. Bradford White, Rheem, and A.O. Smith all carry tank warranties, but internal corrosion after the warranty period generally means replacement is coming.
One thing to check before assuming the tank is the culprit: open a hot tap and let it run for 2 to 3 minutes. If the water clears up, the rust was likely sitting in the pipes near the tap, not coming continuously from the tank.
It Might Be Your Pipes, Not the Tank
Galvanized steel pipes were standard in homes built before the 1970s. Over decades, the zinc coating wears off and the steel underneath rusts. Hot water lines tend to show this problem before cold lines because heat accelerates corrosion.
If you have galvanized supply or distribution lines, you’ll often see rust-colored water in the morning (first draw), which then clears after running for a bit. The pattern matters. Rust that shows up at the start of the day and clears out is classic galvanized pipe behavior. Rust that keeps coming, or gets worse over time, is more likely the tank or a heavily corroded pipe section.
Newer homes with copper or PEX lines rarely have this problem on the distribution side. That said, the short nipples connecting the tank to the supply lines can corrode over time and contribute some discoloration. Dielectric nipples have a plastic inner liner specifically to reduce galvanic corrosion between dissimilar metals; plain steel nipples don’t have that liner and can rust at those connection points.
How a Plumber Diagnoses It
A plumber doing this properly will:
- Run the hot tap until it clears, note how long that takes and whether it clears at all
- Inspect the outside of the tank for rust staining, especially at the top connections and base
- Pull and inspect the anode rod, which requires shutting off the cold supply, depressurizing the tank, and the correct socket
- Check the age of the tank against the serial number (most brands encode the manufacture date in the serial)
- For galvanized pipe concerns, look at exposed pipe runs in the garage, basement, or utility spaces
Navien and other tankless units don’t have anode rods, so if you have a tankless heater and you’re getting rusty hot water, the cause is almost certainly in the pipes or the unit’s heat exchanger, and that’s a different diagnostic path.
What You Can Check Yourself
Before calling anyone, run the hot tap for 2 to 3 minutes and watch what happens. Rust that clears quickly points to sediment sitting near the fixture. Rust that stays, or gets worse, points to the tank or a more corroded pipe section. That one test tells you a lot.
Check the base of the water heater for rust staining or moisture. Note the tank’s age if you can find it on the label (the serial number usually encodes the manufacture year).
Don’t try to pull the anode rod yourself. It can seize in the port after years of no service, and forcing it can crack the tank fitting. That’s a plumber’s job with the right tools.
Don’t ignore persistent rusty water. Rust signals something is actively corroding, and it spreads. A tank corroding internally can develop pinhole leaks.
When to Call a Licensed Plumber
Call a licensed plumber if:
- The discoloration doesn’t clear after running the tap for several minutes
- You find rust or moisture at the base of the water heater
- The tank is over 10 years old
- You suspect galvanized pipes are involved (repiping is not a homeowner repair)
Anode rod replacement, tank replacement, and galvanized pipe repipes all need a licensed plumber. This site is informational only. Verify your plumber’s California license at cslb.ca.gov before any work begins. Takes about 30 seconds and it’s worth doing.