The hot-versus-cold test
- Run cold water first.Open a cold tap for a minute and look at the color and smell in a white cup.
- Then run hot water.Do the same with hot water at the same tap.
- Try another fixture.Repeat at a second tap in a different part of the house.
- Compare.Problems in hot water only point to the heater. Problems in both point to the pipes or the supply.
What the test usually tells you
| Result | Likely source | Next step |
|---|---|---|
| Rusty hot water only | Corroding tank or spent anode rod | Have the tank and anode checked |
| Rusty hot and cold | Old galvanized supply lines | Ask a plumber about the piping |
| Sulfur smell, hot only | Anode rod reacting with water conditions in the tank | Anode inspection, flushing, possible anode change |
| Sulfur smell, hot and cold | Supply or other plumbing | Ask a plumber, and contact the city's water utility if it persists |
| Rust only first thing in the morning | Water sitting in old lines overnight | Note the pattern for the plumber |
About the anode rod
Inside most tanks is an anode rod, a metal rod designed to corrode instead of the tank. As long as it has metal left, it protects the steel. Once it is used up, the tank itself begins to rust, and rusty hot water is often the first visible sign.
The same rod can react with certain water conditions to produce hydrogen sulfide, the source of the rotten-egg smell in hot water. A plumber may suggest flushing, a different anode material, or checking the temperature setting.
What to ask
- Is the anode rod still protecting the tank?
- Is the rust from the tank, or from the pipes?
- Would an anode change or flush solve the smell, or is the tank near the end?
- Are any galvanized lines left in the house?
Common questions
- Is rusty hot water dangerous?
- It is mainly a sign of corrosion, either in the tank or the pipes. The bigger risk is the tank failing, so have it looked at.
- Can I remove the anode rod to stop the smell?
- Removing it leaves the tank unprotected and speeds up corrosion. Ask a plumber about alternatives instead.
- Who do I call if both hot and cold water smell or look wrong?
- Start with a plumber to check your plumbing. If the problem seems to come from the supply, contact the city's water utility.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.