Sewer smell in well water usually means bacteria are breaking down organic matter in your pipes or tank

A sewer or rotten-egg smell from your well water is almost always caused by hydrogen sulfide gas or anaerobic bacteria — organisms that thrive without oxygen and produce sulfur compounds as they decompose organic material. The smell does not mean sewage has contaminated your well, though that is a possibility worth ruling out. More often, the culprit is inside your own system: bacteria growing in your pressure tank, in old pipes, or in the well itself.

The smell is strongest when you first turn on a tap after the water has sat for a few hours, because gas builds up in the tank or pipes. If the smell goes away after running the water for 30 seconds, the bacteria are likely in your plumbing rather than deep in the well. If it persists no matter how long you run the water, the problem is probably in the well itself or in the water table around it.

Key Takeaways

  • Sewer smell in well water is usually hydrogen sulfide gas from bacteria in your tank or pipes, not actual sewage contamination.
  • If the smell clears after running water for 30 seconds, the bacteria are in your plumbing system and can often be treated with chlorine shock or tank cleaning.
  • If the smell persists even after running water, the problem is in the well or groundwater itself and requires testing to determine the next step.
  • A water test from your county health department or a private lab will tell you whether bacteria, hydrogen sulfide, or something else is causing the odor.
  • Do not assume the smell means your water is unsafe to drink — a test result is the only way to know whether the water poses a health risk.

Bacteria in your pressure tank or pipes

If the smell appears only when you first turn on a tap, or only from certain faucets, the bacteria are almost certainly living in your pressure tank or in the pipes between the tank and that faucet. Pressure tanks collect sediment and organic debris over time, and if the tank is old or has not been serviced, bacteria colonize that material and produce hydrogen sulfide gas.

The same thing happens in old galvanized steel pipes, which corrode and create rough surfaces where bacteria stick and grow. Plastic pipes are less prone to this, but it can still occur if water sits in them for long periods — overnight, or in a vacation home that is not used regularly.

You can test this yourself: run the cold water from a tap for a full minute, then fill a glass and smell it. If the smell is gone, the bacteria are in the tank or pipes. If the smell is still there, the problem is in the well or groundwater. This straightforward test tells you whether you need a plumber to service your tank or whether you need a water test first.

Hydrogen sulfide in the well or groundwater

If the smell does not clear after running water, or if it comes from every tap in the house, the hydrogen sulfide is being drawn up from the well itself. This happens when sulfur-reducing bacteria live in the groundwater around your well, or when the well sits in an area with naturally occurring sulfur compounds in the rock or soil.

Hydrogen sulfide in groundwater is common in certain regions — parts of the Midwest, Northeast, and Pacific Northwest see it frequently — but it can occur anywhere. It does not automatically mean your water is contaminated with sewage or pathogens. It is a separate issue, though you should still have the water tested to rule out bacterial contamination.

Wells in areas with high sulfur content sometimes produce this smell from the day they are drilled. Other wells develop it over time as the water table changes or as bacteria populations shift in the soil around the well.

How to tell if it is actually sewage contamination

Sewage contamination is less common than hydrogen sulfide, but it is more serious. If your well is near a septic system, an old sewer line, or a failing drain field, bacteria and pathogens from that system can seep into your groundwater. The smell may be similar to hydrogen sulfide, but the water may also contain E. coli, nitrates, or other harmful organisms.

The only way to know is to have your water tested. Contact your county health department — most offer well water testing, either free or for a small fee. They will test for bacteria, nitrates, and other contaminants that indicate sewage or septic system leakage. A private lab can do the same test if your county does not offer it. The test takes a few days to a week, and results will tell you whether the smell is from hydrogen sulfide alone or from actual contamination.

If your well is within 50 feet of a septic system, drain field, or known sewer line, mention that when you order the test. The lab may recommend additional testing for specific pathogens.

Treating bacteria in your tank or pipes

If the smell clears after running water, a plumber can usually fix it by chlorine shocking your pressure tank and flushing your pipes. This involves injecting a strong chlorine solution into the tank, letting it sit for several hours, then flushing it out completely. The chlorine kills the bacteria and breaks down the biofilm they form.

Some plumbers will also recommend replacing the pressure tank if it is very old or heavily corroded. A tank that is 10 to 15 years old and showing rust or sediment is often cheaper to replace than to repeatedly treat. A new tank costs between $300 and $800 installed, depending on size and your region.

If the smell is coming from old galvanized pipes, you have two options: replace the pipes (expensive, usually $2,000 to $5,000 for a whole house) or install a point-of-use filter at the faucets where the smell is strongest. A carbon filter or a specialized hydrogen sulfide filter can remove the odor from water at that tap without treating the whole system.

Treating hydrogen sulfide in the well or groundwater

If the smell is coming from the well itself, you have several options depending on how strong the smell is and how much you want to spend.

Aeration is the simplest method. An aeration system bubbles air through the water before it enters your tank, which releases hydrogen sulfide gas so it escapes into the air rather than staying in your water. A whole-house aeration system costs $1,500 to $3,000 installed. Point-of-use aerators for a single faucet cost $200 to $500.

Chlorination also works: a chlorine injection system oxidizes the hydrogen sulfide, converting it to a form that a filter can remove. This is more expensive than aeration (usually $2,000 to $4,000 installed) but also removes some bacteria and other contaminants at the same time.

Activated carbon filters can remove hydrogen sulfide if the concentration is not too high. A whole-house carbon filter system costs $800 to $2,000 installed. These filters need regular replacement — every 6 to 12 months depending on how much hydrogen sulfide is in your water.

A plumber or water treatment company can test your water to measure the hydrogen sulfide concentration and recommend which method will work best for your situation.

When to call a professional

Call a plumber if you want to shock your pressure tank or if you suspect the smell is coming from your pipes. A plumber can diagnose which part of your system is affected and recommend the right fix.

Call your county health department or a private water testing lab if you want to rule out sewage contamination, or if the smell is coming from the well itself. Testing is the only way to know what is actually in your water.

If you decide to install a treatment system — aeration, chlorination, or filtration — a water treatment company can size the system to your household's water use and install it correctly. Some plumbers offer this service as well.

Frequently Asked Questions

Is sewer-smelling well water safe to drink?

Not necessarily. Hydrogen sulfide alone is not a health hazard at the concentrations usually found in well water, but the bacteria producing it may indicate other contamination. A water test is the only way to know whether the water is safe. Do not drink it until you have results.

Can I use a whole-house filter to remove the smell?

Yes, if the smell is from hydrogen sulfide in the well. Activated carbon filters or specialized hydrogen sulfide filters work well for mild to moderate odor. If the smell is very strong, aeration or chlorination may work better. A water treatment company can recommend the right filter for your water.

Will the smell go away on its own?

No. Bacteria in your tank or pipes will not disappear without treatment. Hydrogen sulfide in your groundwater is also permanent unless you install a treatment system. The smell may vary with temperature or water use, but it will not resolve itself.

How much does it cost to fix sewer smell in well water?

A chlorine shock treatment costs $200 to $500. A new pressure tank costs $300 to $800 installed. A whole-house treatment system (aeration, chlorination, or filtration) costs $800 to $4,000 installed, depending on the method. A water test costs $50 to $200.

Can a failing septic system cause this smell?

Yes. If your septic system is failing, sewage can seep into your groundwater and cause a sewer smell in your well water. A water test will show whether your water contains bacteria or nitrates from a septic system. If it does, you will need to repair or replace the septic system and may need to disinfect your well.