Hydrogen sulfide in well water

Best for

Homes where both hot and cold water smell, with a hydrogen sulfide level up to about 8 mg/L and pH of 6.5 or higher.

Wrong fit

If only the hot water smells, replace the water heater anode first. If the smell comes from sulfur bacteria that return after shock chlorination, plan for chemical injection.

Tradeoff

Hydrogen sulfide escapes from a sample quickly, so test numbers can read low, and many people size equipment on smell alone.

Find the source first

Before you price a filter, find out where the smell starts. It can come from the aquifer, from sulfur bacteria living in the well or plumbing, or from the water heater. The Minnesota Department of Health suggests a simple check: after you have been away from home for a few hours, smell the water from the hot and cold taps and note which ones smell.

The hot-water-only case is the one most often overspent on. Penn State explains that the water heater’s magnesium rod can chemically reduce natural sulfate to hydrogen sulfide. Swapping it for an aluminum rod should stop the odor while still protecting the tank. Removing the anode entirely also works but shortens the heater’s life and may void its warranty. Minnesota adds that raising the heater to 160°F for several hours kills sulfur bacteria, but warns of scalding and pressure-valve risks; have a plumber do it if you are not familiar with water heaters.

What it looks and smells like

• The rotten-egg smell, strongest when water first runs.
• Black stains on silverware and fixtures, and corrosion of metal plumbing.
• Yellow or black greasy stains where hydrogen sulfide reacts with metals.
• White, gray, black or reddish slime if sulfur bacteria are involved.

Penn State notes that hydrogen sulfide problems are most common in wells drilled into acidic bedrock such as shale and sandstone. It often appears alongside iron; the iron in well water page covers that side.

Is it a health risk?

In drinking water, rarely. Penn State says there is no drinking water standard for hydrogen sulfide because it makes water unpleasant long before it reaches harmful levels, and most people can smell it well below 0.5 mg/L (ppm). The EPA’s secondary standard for odor addresses it only as a nuisance. Minnesota says sulfur bacteria themselves are not harmful and the smell usually does not relate to sanitary quality, but recommends testing for coliform bacteria and nitrate to be safe.

The real hazard is the gas in enclosed spaces. Minnesota warns that hydrogen sulfide can collect in well pits, basements and well houses, and that only well professionals with proper safety precautions should enter a well pit where the gas may be present.

How to test

Hydrogen sulfide is a gas, so it escapes from a sample bottle quickly. Penn State says the test must be done at the home, or the sample must be chemically preserved before it goes to a lab. Ask your lab for a hydrogen sulfide kit with a preservative, and follow the instructions exactly.

Order these at the same time:

• Hydrogen sulfide (field test or preserved sample)
• Iron and manganese, which change the choice of filter
• pH, because most oxidation filters need 6.5 or higher
• Sulfate, which feeds anode and bacteria problems
• Total coliform bacteria and nitrate

The guide to testing your well explains sampling, and the test results tool builds a plan from your numbers.

Sulfate is not the same thing

Sulfate is a dissolved mineral with no smell. The EPA’s secondary standard for sulfate is 250 mg/L, and Minnesota says levels above 250 mg/L can taste bitter or medicinal and have a laxative effect, especially for people not used to it. Minnesota advises using water below 500 mg/L of sulfate for infant formula. Sulfate is removed by reverse osmosis or distillation, not by the sulfur filters on this page. It matters here because bacteria and water heater anodes can convert sulfate into hydrogen sulfide.

Treatment by level

A note on air. Penn State describes simple aeration as usually not efficient enough above about 2 mg/L. Air-injection filters go further than simple aeration: water passes through an air pocket inside the tank, the oxidized particles are filtered out, and the unit backwashes them to a drain. SpringWell publishes an 8 ppm rating for its unit. That figure is the manufacturer’s rating; the extension guidance is more conservative about air alone at higher levels. If your number sits near the top of the range, or the smell is strong after treatment, chemical injection is the more certain route.

For hydrogen sulfide within those published limits and pH of 6.5 or higher, SpringWell’s whole house well water filter is one option that also removes iron and manganese. Above them, look at a chemical injection system. For a deeper look at sulfur-only problems, including peroxide and chlorine systems, see sulfurwaterfilter.com.

Sulfur bacteria

Sulfur bacteria live in low-oxygen wells and plumbing and feed on sulfur compounds. Minnesota says they produce a slime that can clog wells and plumbing and help iron bacteria grow. The first step is to disinfect the well and plumbing with a strong chlorine solution; see shock chlorination. Established bacteria can be hard to remove, and Minnesota notes that pre-work by a licensed well contractor, such as scrubbing the casing, may be needed.

Set expectations: Penn State says that in most cases sulfur-reducing bacteria and the odor return quickly after shock chlorination. If the smell comes back within weeks, continuous chlorination ahead of a filter is the practical long-term answer.

Order of treatment

1. Sediment filter if there is grit.
2. pH correction if pH is below 6.5.
3. Sulfur and iron filter, or chemical injection with a contact tank and filter.
4. Carbon polishing filter, if chlorine is used.
5. Softener, then UV last if needed.

Maintenance

• Air-injection and greensand units need a backwash drain and a working control valve.
• Chlorine systems need the solution tank refilled and the feed pump checked.
• Carbon must be replaced when the smell returns.
• Retest after installation, and keep testing coliform bacteria yearly.

When to call a pro

Call a licensed well contractor if the smell appeared suddenly, if a sewage smell is mixed in, if a well pit is involved, or if sulfur bacteria return after shock chlorination. A licensed plumber can handle water heater anode work. Your state health department can help interpret results.