How to test for hydrogen sulfide

Best for

Well owners who smell sulfur in both hot and cold water and need a number before choosing treatment.

Wrong fit

If only the hot water smells, skip the lab test for H2S and fix the water heater first.

Tradeoff

A preserved lab sample is the most reliable number, but it costs more than a strip test and has to reach the lab quickly.

Step 1: the free smell test

Before paying for any test, find out where the smell starts. A lab number for the well won’t help if the gas is being made in your water heater.

The Minnesota and Vermont health departments describe the same method. Let the water sit unused for a few hours, then smell the hot and cold water at several taps. Vermont’s version of the results:

Add the glass test for a single smelly sink: fill a glass, step away from the sink, swirl and sniff. If the water in the glass is fine, the drain is the source. The homepage smell tool runs through these questions.

Only the last row of the table needs a hydrogen sulfide number. For the others, the fix is a heater repair, a disinfection, or a drain cleaning.

Why hydrogen sulfide is hard to test

H2S is a dissolved gas, and it leaves the water quickly once the water hits air. Virginia Cooperative Extension says it must be tested because it escapes so fast, and recommends lab bottles that contain a stabilizing chemical. Penn State Extension says the test must be done in the home, or the sample must be chemically stabilized before it goes to a commercial lab. UGA Extension adds that refrigerated samples generally have to reach the lab within 48 hours.

Sources don’t fully agree on how practical a lab test is. The Wisconsin DNR’s symptom guide says there is no water test for hydrogen sulfide, and suggests checking whether the water stinks when drawn straight from the well. Most other extension and health sources, including Virginia, Connecticut, Penn State and UGA, describe lab testing with a preserved sample. In practice, call your lab first and ask whether they test H2S and how.

Your three options

For a well that smells in every tap, the best approach is often a certified lab panel for everything else plus an on-site or preserved-bottle H2S reading. Connecticut’s health department says to use a state-certified lab, follow its sampling instructions closely, and test before buying any treatment system.

What to ask the lab for

Hydrogen sulfide alone isn’t enough to choose treatment. Ask for:

Virginia Cooperative Extension notes that the H2S preservative interferes with other tests, so collect a separate sample for bacteria. UGA Extension says sulfate is a routine lab test, but check that your package includes it.

If you order a mail-in kit, read the analyte list before you buy. Tap Score’s well tests are certified-lab packages; confirm hydrogen sulfide and sulfate are on the list for the package you choose. SpringWell’s well water test kit page describes a mail-to-lab test for 53+ contaminants including heavy metals, nitrates and bacteria, but doesn’t name hydrogen sulfide, so ask before relying on it for an H2S number.

How to collect the sample

Your lab’s instructions come first. These general points help the result mean what you think it means:

• Sample the raw water. Use a tap before any softener, filter or treatment unit. An outdoor spigot or the pressure tank drain often works.
• Use cold water. Hot water tells you about the heater, not the well.
• Don’t splash. Fill the H2S bottle gently from a low, steady stream so less gas escapes, and follow the lab’s directions on filling and capping.
• Ship it fast. Collect early in the week so it doesn’t sit in a warehouse over a weekend.
• Write down the smell. Note whether the smell was steady or faded with running. It helps interpret a low result.

Finding a certified lab

Private wells aren’t regulated by EPA, so finding a lab is up to you. Most state health or environmental agencies publish a list of certified or accredited drinking water labs:

• Penn State Extension points Pennsylvania residents to the state Department of Environmental Protection’s list of accredited labs.
• Virginia Cooperative Extension points to the Virginia Division of Consolidated Laboratory Services list.
• Connecticut’s health department says to use a state-certified lab.

Elsewhere, search your state health department’s site for “certified drinking water laboratories”, or call your county extension office, which often runs or knows of a local testing program. When you call a lab, ask three things: whether they test hydrogen sulfide, whether they supply a preserved bottle for it, and how quickly the sample must reach them. A lab that doesn’t offer H2S can still run the iron, manganese, pH, sulfate, bacteria and nitrate tests, and you can get the H2S reading on site.

When to retest

• After treatment is installed, smell the water at several taps, and retest H2S if any smell remains, to confirm the system is keeping up.
• In a different season, if your first result is near a system’s limit. Virginia Cooperative Extension notes H2S is often seasonal.
• When the smell changes. Minnesota recommends a coliform test whenever taste, odor or appearance changes.
• Every year for bacteria, and every other year for nitrate, per Minnesota’s general well testing advice.

Reading your result

Use this as a starting point, then go to the full treatment-by-level table, which shows where sources disagree.

UGA Extension describes 0.5 to 1 ppm as smelling musty or swampy and above 1 ppm as rotten eggs, which can help you sanity-check a lab number against your nose.

Keep in mind that H2S levels can change. Virginia Cooperative Extension notes it is often seasonal. If your result sits near the limit of a system you’re considering, retest in a different season or size for the higher reading. If iron is also present, read sulfur and iron in well water before you buy, because the combined load matters.

If the smell came on suddenly

A smell that appeared out of nowhere, especially after well work or a period of low use, often means sulfur bacteria rather than a change in the aquifer. Test for coliform bacteria, shock chlorinate, and smell the water again after a couple of weeks before spending money on equipment. See shock chlorination for sulfur bacteria.