Rotten Egg Smell in Well Water: What Causes It & How to Fix It

If your well water smells like rotten eggs, you are smelling hydrogen sulfide gas. At the levels you can smell it is a nuisance, not a health threat, but it will not go away on its own. The fix can be a new part for your water heater or a whole-house filter that runs $2,095 to $3,295, and the first thing I ask when someone calls me decides which: do you smell it on the cold, the hot, or both?

Where do you smell it? Tap it.

Only the hot water smells Hot and cold both smell Only one sink smells Not sure? Start here

How to tell where the smell comes from

Smell the cold water and the hot water separately, after the water has sat in the pipes for a few hours. First thing in the morning works; that is when a caller in Virginia noticed it: "At the very beginning when I turn it on, it smells like rotten eggs."

1. Fill a glass from the cold tap at the kitchen sink, step away from the sink, and smell the glass.
2. Do the same with the hot tap.
3. Repeat at a bathroom sink on another floor or at the other end of the house.

The next three sections cover each answer: hot and cold, hot only, and one sink.

When the cold water smells too

When the cold water smells as well as the hot, the hydrogen sulfide is coming from your well. Sulfur bacteria in the groundwater and decaying vegetation in the aquifer make it.

It does not fix itself: if you ignore the sulfur smell, it's only going to get worse, and it's never going to go away. At the high end it is hard to stay in the house; I've been in houses where the level was so high it was unbearable, and you couldn't even breathe.

In that video I answer the questions people ask me about the smell: the hot water question, the bleach question, and why one tank handles sulfur and iron together.

When only the hot water smells

When only the hot water smells, the anode rod, a metal rod inside your water heater, is usually making the gas. Many tank water heaters have a magnesium anode rod to protect the tank from corrosion, and the Minnesota Department of Health explains that the magnesium supplies electrons that help turn sulfate in the water into hydrogen sulfide. It is the less common of the two cases.

The fix is to replace the magnesium rod with an aluminum one, and the smell usually goes away. Do not just pull the rod out and leave it out: Penn State Extension warns that removing it shortens the heater's life and will likely void the warranty. Unless you know water heaters well, have a plumber swap it. The step-by-step is in hot water that smells like rotten eggs.

Check the cold side before you blame the heater. The smell is usually strongest in the shower, even when the gas is coming from the well. If the cold water smells too, it is the well, and a new anode rod will not stop the cold-side smell.

When only one sink smells

When only one sink or one bathroom smells, the smell is usually coming from that drain, not the water. The City of Santa Ana's water department puts it plainly: "It's not the water itself that smells." Food or other organic material decays inside a kitchen drain, and bacteria collect in the P-trap (the curved pipe under the sink) of a bathroom sink.

What to do:

1. Fill a glass at that sink, carry it to another room, and smell it. If the water in the glass smells fine, it is the drain.
2. Clean the drain stopper and the faucet aerator.
3. Flush the P-trap and the overflow with a household bleach solution.
4. If the smell keeps coming back, call a plumber.

Steps 2 to 4 are what Santa Ana's water department recommends.

When the smell started suddenly

A rotten egg smell that appears out of nowhere is usually hydrogen sulfide, but three situations are worth checking first.

• It came on hard and fast. A caller put it exactly that way: "This smell has come on hard and fast," on both hot and cold. The Minnesota Department of Health says to test for bacteria any time the water changes in taste, odor or appearance; see is water that smells like eggs safe.
• It started after a water softener went in. Penn State Extension notes that in rare cases a softener gives sulfur bacteria a place to grow. The Minnesota Department of Health says to ask the installer or the manufacturer how to disinfect it.
• It does not smell like eggs. As I told a caller who thought he had iron bacteria, "Iron bacteria doesn't smell like sulfur. It has a different odor to it... Sulfur smells like rotten eggs."

Is water that smells like eggs safe?

In the water, at the levels you can smell, hydrogen sulfide is a nuisance, not a health threat. There is no drinking water standard for it, because, as Penn State Extension explains, the gas makes water undrinkable long before it reaches harmful levels. In most cases the smell has nothing to do with whether the water is sanitary.

Test anyway. In rare cases the gas comes from sewage or other pollution, so the Minnesota Department of Health recommends testing for coliform bacteria and nitrate. Hydrogen sulfide also does damage while it sits in the pipes: it corrodes metal plumbing and leaves black stains on silverware and fixtures.

The gas in the air is a different matter. Washington's Department of Health lists eye, nose and throat irritation even at levels that smell like rotten eggs, and harder breathing for people with asthma, so open a window or run a fan. In closed spaces the gas can build up to harmful levels; well pits and well houses are places for a well contractor with safety gear, not for a homeowner looking for the source.

No lab report yet: certified lab test, $199

What the certified well test shows

One sample, mailed to you, run by an accredited lab, reports coliform bacteria, nitrate, pH, iron and manganese: the safety check plus the numbers that pick the filter. If you already have a lab report, skip this.

Get the certified well water test

It does not measure the sulfur gas itself; that needs a preserved sample.

An ordinary water sample cannot be used for the sulfur. As I told a caller who asked why the lab test left it out, "sulfur's a gas, and it has to be contained in a vial, and it has to be tested right away." Penn State says the same: the test is done in the home, or the sample is chemically preserved first. If you want the number, the hydrogen sulfide test ($139) preserves the sample and reports the sulfide level with pH.

What does not stop the rotten egg smell

Bleach wears off in about a day, a carbon filter runs out, and a water softener does not remove sulfur at all. A customer told me a neighbor said to just pour bleach into the well. My answer was "No, and stop listening to your neighbor."

• Pouring bleach down the well. It kills the smell for maybe 24 hours, then it comes back. With iron in the water, bleach makes the iron worse.
• A carbon filter. It helps at low levels, then runs out. Once it is used up it can put the sulfur back, and the smell gets worse than before.
• A water softener. It does not take sulfur out. The softener fills up with sulfur it cannot rinse down the drain.

Some of the people who call me have already tried one of these. A caller in Florida: "they shocked it with the chlorine, but the rotten eggs came back." Another had a carbon tank that "got rid of the smell for 6, 8 months, and then it slowly came back... Then it got even worse."

What stops the rotten egg smell for good

If only the hot water smells, the anode rod is the fix and you can skip this section. If the cold water smells too, you need a whole-house filter, and how much sulfur you have decides which kind (ppm means parts per million):

• Under about 1 ppm: a carbon filter can handle it, but the carbon runs out and is replaced; a small filter can last only weeks.
• Up to 10 ppm: an air-injection filter, with no chemicals.
• Above 10 ppm: chlorine or peroxide pumped into the water and then filtered, with a chemical tank you refill every month.

Ten parts per million is a lot of sulfur. A January caller did not know his number, and I told him, "you don't have anywhere near 10 because when you get to 1 to 2, it blows you out of the house."

For a smell from the well, the filter I recommend is the Fleck 2510AIO air-injection filter with Katalox Light, which removes up to 10 ppm of sulfur, 30 ppm of iron and 15 ppm of manganese in one tank, with no chemicals. The valve keeps a pocket of air at the top of the tank. As the water passes through the Katalox Light (the filter media inside the tank), the media pulls sulfur, iron and manganese out and holds it, and the tank backwashes itself to a drain to clean itself out, every day or every other day depending on how it is set.

The pH matters. I want a pH around 8 when I'm treating sulfur. If the water is acidic, the filter only works for a short period of time, and then the sulfur and the iron start coming through again. If your pH is below 7, an acid neutralizer goes in ahead of the sulfur filter. Of the wells my customers have had lab-tested, about one in six came back acidic, below pH 7 (71 of 397).

The size depends on how many people live in the home, how many bathrooms you have and how much water you use. The sulfur filters we sell run from $2,095 for the 1.5 cubic foot to $3,295 for the 3.5, and most people choose the 2.5 cubic foot at $2,495. We also sell a four-stage sulfur system (sediment filter, the 2.5, a carbon tank and a UV light) for $4,495. For how the AIO compares with chlorine, carbon and aeration, see every sulfur treatment compared.

What ships: the tank, the control valve, and the Katalox Light in separate bags, which is loaded into the tank at install. 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 plumbers call me all the time with questions; I talk them through it.

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.

Know whether it is hot, cold or both?

Tell me where the smell is

Text me where you smell it and your test numbers if you have them. I will tell you whether it is the heater, the well or a drain, and which size filter, if any, you need.

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

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