Rotten-egg smell in well water
A rotten-egg smell comes from hydrogen sulfide gas. First, check whether it's only in your hot water. If it is, the cause is usually your water heater, and the fix can be cheap.
Step 1: Hot water only, or hot and cold?
Run cold water from a faucet and smell it. Then run hot water and smell it again.
| What you notice | Most likely cause | Usual fix |
|---|---|---|
| Hot water only | The magnesium rod (anode) in your water heater reacting with the water | Replace the anode rod with an aluminum-zinc type. Often a small, inexpensive repair. |
| Both hot and cold | Hydrogen sulfide in the groundwater, or sulfur bacteria in the well | Shock-chlorinate the well first. If the smell returns, an air-injection or chlorination system. |
| Strong at first, then fades as water runs | Bacteria in the well or pipes | Shock chlorination, then retest. |
Is it dangerous?
At the levels usually found in well water, hydrogen sulfide is mainly a nuisance. It smells bad, tarnishes silver, and corrodes plumbing. But the smell can also come from bacteria, so a bacteria test is a good idea.
What to test for
Test for bacteria, sulfate, iron, and pH. Hydrogen sulfide gas escapes quickly, so a standard lab test often can't measure it accurately. How strong the smell is matters more.
When to call a professional
If the smell is in your cold water and comes back after shock chlorination, a water treatment professional can recommend the right system. Ask them to explain why a particular system fits your water.
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