Water smells like rotten eggs? Here's what's going on.
That smell is hydrogen sulfide gas. It's common in Florida wells, usually not a health risk at the levels found in homes, and very fixable once you know where it's coming from.
Hot side, cold side, or both?
Where you smell it tells you a lot. The Florida Department of Health suggests a simple check: run the cold tap, then the hot tap, and sniff each. If you have a softener, also try a tap that skips it, like an outdoor spigot.
Then notice whether the smell is strongest at first and fades, or stays the same. Heat drives the gas out of water, so the hot side often smells stronger either way.
- Hot water onlyUsually the water heater: its magnesium anode rod reacts with sulfate in the water. A plumber can swap it for an aluminum or zinc anode.
- Only in softened waterOften sulfur bacteria growing in the softener. It needs sanitizing.
- Strong at first, then fadesSulfur bacteria in the well or plumbing. A smell that comes and goes over time points here too.
- Constant, hot and coldHydrogen sulfide in the groundwater itself, the classic Florida well problem.
- On city or county waterRare from the supply. If only the hot side smells, it's usually the water heater's anode rod. Check the heater and drains first.
Where the smell comes from.
Some hydrogen sulfide occurs naturally in groundwater. A lot of it is made by sulfur bacteria. Penn State Extension explains that they thrive in the low-oxygen conditions inside wells and plumbing, and give off the gas as they feed on sulfate.
Our area has plenty of sulfate. A U.S. Geological Survey study of the Peace and Myakka River basins and nearby coast found sulfate in the Upper Floridan aquifer and the aquifer system above it is commonly above 250 milligrams per liter, especially near the coast.
- Bacteria in the well or pipesBesides the smell, the Minnesota Department of Health says sulfur bacteria make a slime that can help iron bacteria grow and clog wells and plumbing.
- PollutionRare, per the Florida Department of Health. But Connecticut's health department notes the odor can come from sewage, one more reason to test for bacteria.
How much is in your water?
Your nose tells you it's there, not how much. The amount decides which fix will work. These ranges are from the Connecticut Department of Public Health; labs report milligrams per liter (mg/L), the same as ppm for water.
The gas escapes fast, so the sample has to be chemically stabilized right away (Connecticut) or tested on site (Penn State). Otherwise it can read low.
- About 0.5 mg/LWhere most people first smell it.
- Under 1 mg/LMay smell "musty" or "swampy" rather than like eggs.
- 1 to 2 mg/LA clear rotten-egg smell, and very corrosive to household plumbing.
- What it damagesConnecticut says it corrodes iron, steel, copper and brass, tarnishes silverware, leaves yellow or black stains on fixtures, and can discolor coffee and tea.
- No federal limitThere's no drinking water standard. Penn State notes most people smell it long before it reaches harmful levels.
Hot water only? Start with the heater.
Most tank water heaters have a magnesium anode rod that corrodes so the tank doesn't. The Minnesota Department of Health explains that the magnesium can help turn sulfate in the water into hydrogen sulfide. That's why this happens on city and county water too.
Don't just pull the rod out. Penn State Extension warns that removing it speeds up corrosion, shortens the heater's life, and will likely void the warranty.
- Swap the anodeConnecticut and Penn State both say an aluminum anode (Connecticut also lists zinc) can fix it. Connecticut adds: above 150°F, use only aluminum. Have a licensed plumber do it.
- Flushing or heating the tankMinnesota says disinfecting the tank or running it at 160°F for several hours can help, but both carry scalding and safety risks. Check with the manufacturer or a pro first.
- If the cold side smells tooA new anode won't help. The problem is in the well, plumbing or groundwater.
How it's fixed.
The right method depends on how much is in your water, so we measure it first. Sources differ on exact cutoffs, so we've noted whose numbers are whose. If a simpler option can handle your level, we'll tell you.
- Air-injection oxidizing filterThe go-to for typical well levels. It also removes iron in the same tank. For oxidizing filters, Penn State puts the ceiling around 2 to 3 mg/L; Connecticut lists greensand filters for 1 to 10 mg/L.
- Chlorine or permanganate injectionFor high levels (around 6 ppm and up), followed by filtration. Connecticut and Penn State both cite about 20 minutes of contact time for chlorine.
- Activated carbonOnly for very low levels: 0.3 mg/L or less per Connecticut, or under about 1 mg/L with a large tank per Penn State. It fills up quickly otherwise.
- Catalytic carbonHandles more than standard carbon, but Penn State says the water needs at least 4.0 mg/L of dissolved oxygen.
- Shock-chlorinating the wellTreats sulfur bacteria growing in the well itself. Penn State calls it temporary: the odor usually returns quickly, so it's often paired with a filter.
Shock-chlorinating a well: do it by the book.
Shock chlorination puts a strong bleach solution down the well and through every pipe in the house. If you do it yourself, follow the Florida Department of Health's well disinfection procedure exactly, including its bleach amounts. Don't guess at a dose.
- Some wells need a proThe DOH method is only for a submersible pump with a removable threaded plug in the sanitary seal. Otherwise, use a licensed well contractor or pump installer.
- Don't use the water yetChlorine can damage eyes and skin. Don't drink, cook, shower or bathe with heavily chlorinated water.
- Test before you drinkAfter flushing, the DOH says to have the water tested by a certified lab.
- Expect it to come backConnecticut and Penn State both say the bacteria may return.
Testing a well in Manatee or Sarasota County.
The Florida Department of Health says the smell usually doesn't relate to how clean the well is. It doesn't prove the water is safe, either. Your county health department can explain how to sample and help you read results.
- Every yearBacteria and nitrate, at a state-certified lab.
- When something changesAgain if taste, odor or color changes, and after the well is disinfected.
- Every three yearsLead, for most well owners.
- Buying a home with a wellFlorida doesn't require it, but the DOH recommends testing for coliform bacteria, nitrate and lead.
Common questions.
Is rotten-egg water safe to drink?
Hydrogen sulfide on its own doesn't cause disease, and the Florida Department of Health notes that sulfur bacteria aren't harmful and the smell doesn't tell you how clean the water is. So test for bacteria anyway, especially if the smell is new.
Why does only my hot water smell?
Most often it's the water heater's magnesium anode rod reacting with sulfate in the water. A different anode, plus treating the water upstream, usually solves it.
Will a regular filter fix it?
Not for long. Small cartridge carbon filters clog quickly with sulfur. An oxidizing filter is the lasting fix for most wells.
How often should I test my well?
Florida health officials recommend testing private wells for bacteria and nitrate at least once a year at a state-certified lab, and again any time the taste, odor or color changes.
Is it safe to shower in water that smells like sulfur?
At household levels, most people smell hydrogen sulfide long before it reaches harmful levels, according to Penn State Extension. The bigger risk is gas building up in enclosed spaces. The Minnesota Department of Health says it can collect in well pits, basements and well houses, and only trained professionals should enter those spaces.
Can I just remove the anode rod from my water heater?
We don't recommend it. Penn State Extension warns that removing the anode speeds up corrosion, shortens the heater's life and will likely void the warranty. Ask about a replacement aluminum or zinc anode instead.
Sources
- Florida Department of Health: Well water facts, odor and staining
- Connecticut Department of Public Health: Hydrogen sulfide in private wells
- Florida Department of Health: Private well testing
- Florida Department of Health: Well disinfection
- Penn State Extension: Hydrogen sulfide (rotten egg odor) in water wells
- Minnesota Department of Health: Hydrogen sulfide and sulfur bacteria in well water
- U.S. Geological Survey: Sources of sulfate in the Upper Floridan aquifer, southwest Florida (WRI 96-4146)
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