Hydrogen Sulfide in Well Water: Causes, Health Effects & Treatment

Hydrogen sulfide is the gas that makes well water smell like rotten eggs; most people, me included, just call it sulfur. Bacteria and decaying vegetation underground make it, and it comes up dissolved in your water. At the levels wells have, it is a nuisance, not a health threat, but from about 1 ppm (part per million) it can corrode copper pipes and tarnish silver, and it will not go away on its own. How much you have decides the fix: a carbon filter below about 1 ppm, an air-injection filter up to 10 ppm, and chlorine pumped into the water above that.

What is hydrogen sulfide in well water?

Hydrogen sulfide is a gas dissolved in the water, the way the fizz is dissolved in a soda. Sulfur bacteria and decaying vegetation underground make it. The bacteria live in the low-oxygen water inside wells and plumbing, and Penn State Extension and the Vermont Department of Health both say the bacteria themselves are not harmful.

Because it is a gas, an ordinary sediment filter cannot catch it. It has to be soaked up by carbon, turned into solid specks a filter can catch, or let out of the water into the air, and which of those fits depends on how much you have.

Where you smell it tells you where it comes from. When the cold water smells as well as the hot, it is coming from the well. When only the hot water smells, the water heater is usually making it: the Minnesota Department of Health explains that the magnesium anode rod inside many water heaters supplies electrons that help turn sulfate in the water into hydrogen sulfide, and swapping it for an aluminum rod usually solves it. That case, and the case where only one sink smells, are covered in rotten egg smell in well water.

Sulfate is a different thing. It is a mineral dissolved from rock and soil, and it is what the certified well water test reports, so a sulfate number on your lab report is not your hydrogen sulfide level. The EPA's guideline for sulfate is 250 mg/L, and above that it can have a laxative effect.

Is hydrogen sulfide in well water dangerous?

In the water, hydrogen sulfide is a nuisance, not a health threat. There is no drinking water standard for it at all; it is not even on the EPA's list of secondary standards, the non-enforceable guidelines for taste and odor. Penn State Extension explains why: the gas makes water undrinkable long before it reaches harmful levels. The University of Georgia's water lab says drinking water with high levels can cause nausea and stomach pain, but that it is highly unlikely anyone could drink a harmful dose.

Test for bacteria anyway. In most cases the smell has nothing to do with whether the water is sanitary, but in rare cases the gas comes from sewage or other pollution, so the Vermont and Minnesota health departments recommend testing the well for total coliform bacteria and nitrate. The certified well water test covers both, along with the pH and iron that matter for treatment.

Showering in sulfur water

Hot water drives the gas out into the air, which can make the smell worst in the shower (Connecticut Department of Public Health). Breathing it is a different matter from drinking it. Washington's Department of Health lists eye, nose and throat irritation even at levels that smell like rotten eggs, and people with asthma may have a harder time breathing. Run the bathroom fan or open a window, and if someone in the house has asthma, do not put off treating it.

The real danger is a closed space. The gas is heavier than air and collects in low, enclosed places such as well pits, basements and well houses, and at very high levels people stop being able to smell it, so the smell stops being a warning. The Minnesota Department of Health says only well professionals using proper safety precautions should go into a well pit or other enclosed space where the gas may be.

What your hydrogen sulfide level means

At about 1 ppm, hydrogen sulfide starts to corrode copper pipes. That is also about where the smell turns to rotten eggs and silverware starts to tarnish. Below that, the Connecticut Department of Public Health and the University of Georgia's water lab both describe a musty or swampy smell. Labs report it as ppm or mg/L, which are the same number for water.

A caller in September had his lab report in hand: "The H2S was 1 parts per million." That was enough for the rotten egg smell. He also had manganese and hard water, so for him it was one air-injection filter, then a softener, then a carbon tank to clean up anything left over.

Ten parts per million is the most one air-injection filter handles, and most wells are not at the top of that range.

How to get your hydrogen sulfide level tested

An ordinary water test misses hydrogen sulfide, because the gas escapes from the bottle. The sample has to be preserved the moment it is collected. The Connecticut Department of Public Health says the sample must be chemically stabilized right after collection, and Penn State Extension says the test is done in the home or the sample is stabilized first. The certified well water test, which reports 53 things including pH, iron, sulfate, coliform bacteria and nitrate, does not include hydrogen sulfide.

The hydrogen sulfide test ($139) is built to preserve the sample. You collect it, mail it back with the prepaid label, and an accredited lab reports dissolved sulfide and pH, usually in about 10 business days. The sampling steps are in how to test for hydrogen sulfide.

Is the number worth $139? The Connecticut health department says the amount is what decides which treatment will work, which is the question the table above answers. If it were my own house, I would test first: "find out exactly what the levels are in my water of iron and sulfur, check the pH, 'cause that's important." The sulfur number comes from this test; iron and pH come from the certified well water test.

Know your level, or just where it smells?

Text me your test numbers

Send me your hydrogen sulfide, iron and pH numbers, or tell me where you smell it. I will tell you whether you need carbon, a filter or nothing at all, and what size.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

How to get rid of hydrogen sulfide

Up to 10 ppm, which covers most wells, one air-injection filter takes the hydrogen sulfide out with no chemicals. The same tank removes up to 30 ppm of iron and 15 ppm of manganese. It is the Fleck 2510AIO, and it works better than anything else we have tried.

The valve keeps a pocket of air at the top of the tank. The air turns the gas into solid specks, the Katalox Light (the filter media inside the tank) catches them along with the iron and manganese, and every day or two the tank rinses what it caught down the drain.

A caller in August had lived with hydrogen sulfide that was "really tremendous" since the house was built, handled by a big aeration tank and chlorine injection. What I told him about this filter: "It removes up to 10 parts per million of sulfur, which is an extreme amount."

In this video I answer the questions people ask me about getting rid of it: whether it is the water heater, why bleach down the well wears off, and why one tank handles sulfur and iron together.

Acidic water gets fixed first

I want the pH around 8 when I'm treating sulfur. If the water is acidic, the filter only works for a short time, and then the sulfur and iron start coming through again, so when the pH is below 7 an acid neutralizer goes in ahead of the filter. A caller in Massachusetts had a pH of 6.0 and a carbon tank that had just been serviced and still smelled. My first answer was "You have to get the pH up first," and then the order: "treat the pH first with a 1.5 or 2.5 backwashing acid neutralizer. Then it would go through the iron sulfur filter and then through your softener."

Other ways to remove hydrogen sulfide

• Carbon. Catalytic carbon works really well for average levels of sulfur, but it runs out: it lasts 4 to 5 years, where Katalox Light lasts 6 to 8. Once carbon is used up it can put the sulfur back into the water, and the smell comes back worse than before.
• Chlorine or peroxide injection. This is the usual answer above 10 ppm, past what the air-injection filter is rated for; Penn State Extension says chlorination can handle any level and is most often used above 6 ppm. A pump feeds the chemical into the water, a blending tank gives it time to work, and a big carbon tank takes the chlorine back out. The chemical tank has to be refilled and the system serviced every month.
• Aeration and greensand. Connecticut and Penn State put aeration at below about 2 ppm. Minnesota and Vermont put a greensand filter at up to about 6 ppm, and it has to be recharged with potassium permanganate.

Every method, side by side, is in every sulfur treatment compared.

What ships with the filter

The sulfur filters we sell come in four sizes, from the 1.5 cubic foot at $2,095 to the 3.5 at $3,295, and most people choose the 2.5 cubic foot at $2,495. The size depends on how many people live in the home, how many bathrooms you have and how much water you use.

What ships: the tank, the Fleck 2510AIO control valve, a stainless steel bypass valve, and the Katalox Light in separate bags, which is loaded into the tank at install through the included fill funnel. Drain tubing is not included; the plumber runs it to a floor drain, utility sink or standpipe. We recommend a licensed plumber for the install, and I support your plumber by phone at 800-460-5810.

After that, the only maintenance is new Katalox Light every 6 to 8 years, or in some cases every 8 to 10: the old media is dumped out and the tank is refilled.

Frequently asked questions