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The short answer
Why does my water smell like rotten eggs? The smell is hydrogen sulfide gas, usually made by sulfur bacteria in a well, the plumbing, or the water heater, or present naturally in groundwater (Minnesota Department of Health). If only the hot water smells, the water heater is the likely source. If hot and cold both smell, it’s probably the well. At household levels it’s mainly a nuisance and corrosion problem, not a health hazard (Penn State Extension). The fix depends on the source and the level: an anode change for the heater, and carbon, oxidizing filters, or chlorination for the well.
Where is the rotten egg smell coming from?
The Minnesota Department of Health suggests a simple test after the water hasn’t been used for a few hours (MDH):
| What you notice | Likely source |
|---|---|
| Cold water has no smell, hot water does | The water heater |
| The smell goes away when you bypass the softener | Bacteria in the softener |
| All cold taps smell, but it fades after running | Sulfur bacteria in the well or plumbing |
| All cold taps smell, and it doesn’t fade | Hydrogen sulfide in the groundwater |
Wells drilled into shale or sandstone are most prone (Penn State). Other signs include black stains on silverware and fixtures and slime that can clog plumbing (MDH). If you suspect sewage, test for coliform bacteria and nitrate (Connecticut DPH).
Why does only my hot water smell like rotten eggs?
A water heater’s magnesium anode rod can chemically reduce sulfates to hydrogen sulfide. Fixes:
- Replace the anode. A licensed plumber can fit an aluminum or zinc rod; use aluminum only if the tank runs above 150°F (Connecticut DPH, UGA). Check the warranty first: Penn State warns removing the anode will likely void it.
- Heat-treat the tank. MDH says raise the temperature to 160°F for several hours, then flush, and lower it afterwards to prevent scalding (MDH). Wisconsin says do this only if the heater has a pressure relief valve (Wisconsin DNR). Water at 140°F can cause serious burns in about 6 seconds (CPSC).
- A new anode won’t help if bacteria living in the heater are making the gas (Virginia Tech).
Is it safe to drink water that smells like sulfur?
At the levels found in household water, hydrogen sulfide is a nuisance rather than a health hazard, and there’s no drinking water standard because the smell makes water undrinkable first (Penn State). Sulfur bacteria do not cause human health concerns. Most people smell it at about 0.5 mg/L, and it smells strongly of rotten eggs at 1 to 2 mg/L, when it’s also very corrosive (Connecticut DPH). Above 0.5 mg/L it can corrode iron, steel, copper, and brass (UGA). The gas is toxic in enclosed air, so don’t enter well pits without precautions (MDH, ATSDR). Sulfate, a related mineral, has an EPA guideline of 250 mg/L and can have a laxative effect, mainly when you first switch to high-sulfate water (EPA).
How do you remove the sulfur smell from well water?
Test first. Hydrogen sulfide escapes from a sample, so it needs a chemically preserved lab sample or an in-home test (Connecticut DPH, Penn State). Then match the treatment to the level; extension services give different ranges, so treat these as approximate:
| Level | Treatment | Notes |
|---|---|---|
| Low: up to about 0.3 to 1 mg/L | Activated carbon filter | 0.3 mg/L per Connecticut DPH and UGA; about 1 mg/L per Penn State and MDH. Carbon needs replacing as it fills |
| Moderate: up to about 2 to 10 mg/L | Oxidizing filter such as manganese greensand | Ranges vary: 2 to 3 mg/L (Penn State) to 10 mg/L (Connecticut DPH, UGA). Regenerated with potassium permanganate; may need a neutralizer if pH is below 6.7 (Penn State) |
| Up to about 2 mg/L | Aeration | Extension sources say aeration usually isn’t used above about 2 mg/L (Penn State) |
| High: above about 6 mg/L | Continuous chlorination or permanganate injection, with a contact tank and filter | Chlorination can treat any level, with about 20 minutes of contact (Penn State) |
Shock chlorinating the well can reduce sulfur bacteria, but the smell and bacteria usually return quickly, so continuous treatment may be needed. Some states regulate well treatment; Wisconsin, for example, requires approval for continuous pellet chlorination (Wisconsin DNR).
What about whole-house sulfur filters?
SpringWell rates its well water system for hydrogen sulfide up to 8 ppm, iron up to 7 ppm, and manganese up to 1 ppm, using air injection and greensand media. Those are the maker’s ratings; no certifier lists it, and its 8 ppm air-injection figure is higher than extension services suggest for aeration. See our SpringWell well water review and the best water filters for well water. For a mail-in lab test, see the Tap Score Advanced.
Common questions
Why does my water smell like rotten eggs?
Hydrogen sulfide gas, usually from sulfur bacteria in the well, plumbing, or water heater, or present naturally in groundwater (MDH).
Why does only my hot water smell like rotten eggs?
The heater’s magnesium anode can react with sulfate to make hydrogen sulfide. A plumber can swap it for aluminum or zinc; check the warranty first.
Is it safe to drink water that smells like sulfur?
At household levels it’s a nuisance, not a health hazard, according to Penn State. Test for coliform and nitrate if sewage could be involved.
Will a carbon filter remove sulfur smell?
Only at low levels, about 0.3 to 1 mg/L depending on the source. Higher levels need an oxidizing filter or chlorination.
Will shock chlorinating my well get rid of the smell?
It can help for a while, but the smell often returns quickly; continuous treatment may be needed (Penn State; Virginia Tech).