Is sulfur water safe?

Best for

Well owners who want to know whether to keep drinking smelly water while they sort out the cause.

Wrong fit

If anyone in the house is sick with stomach illness, or the well was flooded, treat it as possible contamination and call your state or county health department first.

Tradeoff

A clean coliform and nitrate test answers the safety question, but it doesn't remove the smell or the corrosion, which still need a fix.

The short answer

Hydrogen sulfide in household water is an aesthetic problem in almost every case. Penn State Extension says there’s no drinking water standard for it because the water becomes unpleasant to drink long before it reaches harmful concentrations, and that the human nose detects the gas well before it causes health concerns. Most people can smell it well below 0.5 mg/L (ppm).

UGA Extension puts it the same way: high levels in drinking water can cause nausea and stomach pain, but a harmful dose is unlikely because the taste and smell put you off first. The Connecticut Department of Public Health says water containing dissolved H2S alone doesn’t cause disease.

That’s the gas. Three related questions matter more for safety: what else might be in the water, what the gas does in the air, and how much sulfate is present.

What the health agencies say

The agencies agree. The smell is not a sign of danger by itself, but it is a reason to test.

When the smell can point to something worse

Hydrogen sulfide usually comes from natural sources: bacteria acting on sulfate in low-oxygen groundwater, certain rock formations, or the water heater. Virginia Cooperative Extension notes it can also come from sewage contamination, especially in shallow or poorly built wells. UGA Extension says this is rare and mostly limited to shallow wells near leaky sewer lines or septic drainfields.

So treat the smell as a prompt to test for:

• Total coliform bacteria (and E. coli). The Minnesota Department of Health recommends a coliform test every year and whenever the taste, odor or appearance of the water changes.
• Nitrate. Minnesota recommends testing every other year, and says bottle-fed infants under six months are at highest risk from levels above 10 mg/L.

Private wells aren’t regulated by EPA. EPA’s private well page says owners are responsible for the safety of their own water. Use a state-certified lab, and call your state or county health department if a result comes back positive.

Act sooner if: someone in the house has unexplained stomach illness, the well was flooded, or the smell is more like sewage than eggs. In those cases use bottled water for drinking and infant formula until a bacteria test comes back clean.

The gas in the air: well pits, basements and showers

The real hazard from hydrogen sulfide is breathing high concentrations in a closed space. The federal Agency for Toxic Substances and Disease Registry (ATSDR) gives these air levels:

Those are air concentrations, not water concentrations, so don’t compare them with a water test result. The point is the third row. At high levels your nose stops warning you.

For a household, the practical rules are simple:

• Don’t climb into a well pit. The Minnesota Department of Health says only well professionals using proper safety precautions should enter a well pit or other enclosed space where the gas may be present.
• Vent the gas. Minnesota says it’s important to remove the gas from the water or vent it to the outside, which keeps it from collecting in well pits, basements and well houses. Ask a licensed well contractor whether your well cap is vented.
• Ventilate the bathroom. Connecticut notes the odor is often strongest when hot water runs, especially in the shower. Run the fan.

Sulfate is a different question

Sulfate is a dissolved mineral, not a gas, and it doesn’t smell. It’s often present where H2S is, because bacteria make H2S from sulfate. Sulfate is the one with a direct health effect.

• EPA’s secondary (non-enforceable) standard for sulfate is 250 mg/L, for taste.
• In its 2003 review, EPA reported that EPA and CDC jointly concluded adverse effects are unlikely in adults below 600 mg/L, and an expert panel suggested a health advisory where sulfate exceeds 500 mg/L.
• UGA Extension says sulfate above 250 ppm may have a laxative effect and can cause dehydration, and calls this especially hard on infants and young animals.
• EPA lists formula-fed infants, older people using powdered nutritional supplements, and visitors not used to high-sulfate water as the sensitive groups. Virginia Cooperative Extension notes most people adjust over time.

The thresholds differ between sources because 250 mg/L is a taste-based guideline and 500 to 600 mg/L are health-based figures. More detail is on sulfate vs hydrogen sulfide.

Cooking, coffee, laundry and animals

Hydrogen sulfide changes more than the smell of the tap water.

• Coffee, tea and cooking. Virginia Cooperative Extension says H2S can alter the taste and appearance of hot drinks and cooked food. Connecticut notes it can discolor beverages and cooked foods. This is a quality issue, not a safety one, and it’s often the first thing people notice.
• Laundry. UGA Extension says H2S can cause yellow or black stains on laundry and bathroom fixtures, and Virginia notes sulfur bacteria can produce dark slime that stains clothing.
• Bathing. Showering in sulfur water isn’t a known health risk at household levels. The gas comes off most from hot water, so run the bathroom fan.
• Pets and livestock. Hydrogen sulfide at household levels isn’t singled out as a risk for animals in these sources, but sulfate is. UGA calls sulfate above 250 ppm especially hard on young animals, and Virginia says most livestock adjust over time. Ask your county extension office if you water young stock from a high-sulfate well.

If the taste of food and drinks is the main complaint, a carbon filter at the kitchen tap can help as a stopgap at low levels while you sort out whole-house treatment, though Minnesota notes small carbon filters may be used up within days or weeks. It won’t help the shower or laundry.

The real cost is corrosion

The health risk is small, but the damage to plumbing is real. Virginia Cooperative Extension says H2S makes water more corrosive and can leach metals from plumbing, corrode stainless steel, darken silverware, and discolor copper and brass fixtures. Connecticut says it corrodes iron, steel, copper and brass. Penn State notes yellow or black greasy stains on fixtures.

If your home has older plumbing, corrosive water can be a reason to test for lead and copper at the kitchen tap. Minnesota recommends testing every well for lead at least once anyway.

What to do, in order

1. Find the source. If only the hot water smells, it’s the water heater and the water from the well is fine. See hot water smells like rotten eggs.
2. Test for safety. Coliform bacteria and nitrate from a state-certified lab. Add sulfate if anyone is using the water for infant formula.
3. Test for treatment. If the well is the source, test hydrogen sulfide, iron, manganese and pH. See how to test for hydrogen sulfide.
4. Deal with bacteria first. If coliform is present, or the smell started suddenly, shock chlorinate and retest. See shock chlorination for sulfur bacteria.
5. Then treat the smell using the treatment-by-level table.

For health questions about a specific result, call your state health department. They handle these questions every day.