Well water smells like rotten eggs? Find the source first
Hydrogen sulfide. It is common in Floridan aquifer water and it is not a sign that anything has broken. Before you spend a dollar, run one tap and then another, because that single comparison decides whether this is a cheap fix in your garage or a treatment system on your main line.
In short
- The smell is hydrogen sulfide, common in Floridan aquifer water and classed as a nuisance rather than a health contaminant.
- If only the hot tap smells, the usual cause is the water heater's anode rod, not the well.
- If hot and cold both smell, the fix is aeration, an oxidizing filter or chlorination. A softener will not remove it.
Do this first. It takes two minutes and costs nothing.
Smell the cold tap and the hot tap separately. Hot only means the anode rod in your water heater, which is a cheap fix and nothing to do with the well. Both hot and cold means hydrogen sulfide in the water arriving at the house, which needs treatment. Most people can smell it well below 0.5 milligrams per liter, which is far under any level that would matter to health, so your nose finds this long before a laboratory would.
Run the cold tap, in a room you have not run hot water in recently, and smell it. Then run the hot tap and smell that. Then do the same in a second room, and outside at a hose bib if you have one that comes off the line before any treatment equipment.
| Where it smells | Almost certainly | What that means for you |
|---|---|---|
| Hot water only | The magnesium anode rod in the water heater reacting with sulfate in the water | A plumber, an afternoon, and one part. Nothing to do with your well, and no treatment system needed. |
| Hot and cold, everywhere | Hydrogen sulfide in the water arriving at the house | Treatment on the main line. The level decides which kind. |
| One tap only | Bacteria in that fixture or its drain, not in the water | Clean the aerator and the drain and smell a glass of the water in another room. |
| Only after the house has stood empty | Stagnation in the pipework or a little-used branch | Flush it through thoroughly before concluding anything. |
The hot-only case is a cheap repair and it is genuinely common. Anybody who quotes you a whole-house sulfur system without first asking which taps smell has skipped the diagnosis, and you should treat the rest of their quote with the same suspicion.
Where it comes from here
Hydrogen sulfide is produced when sulfate-reducing bacteria in the aquifer or in the well casing metabolize the naturally occurring sulfate minerals in the Floridan's carbonate rock. That is a local explanation rather than a general one, and it is why this is so much more common in central Florida than in the states whose extension pages dominate the search results.
It also means it is not contamination in the sense people fear. The gas is detectable by smell at concentrations far below the level at which it would be a health concern in water, which is the useful thing to know at eleven at night when the shower has just started smelling.
USGS, Water-resources information for the Withlacoochee River region · Penn State Extension, Hydrogen sulfide in water wells
Hydrogen sulfide does not have a drinking water standard because it makes the water aesthetically undrinkable long before it reaches harmful concentrations.
Penn State Extension, Hydrogen sulfide in water wells
Penn State Extension, Hydrogen sulfide in water wells
What actually removes it
Aeration, an oxidizing filter, or chlorination, chosen by how much sulfide the test shows rather than by how bad it smells. A water softener does not remove it. If only the hot tap smells, none of these apply and the answer is a magnesium anode rod, the cheapest fix on this page by an order of magnitude, and a water heater job rather than a well job.
In rough order of how much sulfide they will handle, and therefore of cost. The right one is chosen from a test result, not from a description over the phone.
- Replacing the water heater anode rod. Only relevant to the hot-only case, and the cheapest outcome available. An aluminum or zinc rod in place of the magnesium one usually settles it.
- Aeration. Exposing the water to air so the gas comes out of solution, then venting it. Effective at low to moderate levels, no chemicals, and the maintenance is mechanical rather than consumable.
- An oxidizing filter. A media bed that converts the sulfide so it can be filtered out. Handles moderate levels and often deals with iron in the same unit, which is why it is common here.
- Chlorination followed by filtration. The heavy end. Used for high sulfide, and worth it when there is iron bacteria in the picture too. More equipment, and it needs attention rather than being fitted and forgotten.
A water softener does not remove hydrogen sulfide. Neither does a plain carbon or sediment filter at anything beyond trace levels, though a small carbon filter at one tap can make the drinking water pleasant while you sort out the real answer.
If it is on the cold tap too
Get a test that gives you a hydrogen sulfide figure, an iron figure and a pH, because those three together choose the equipment and its order. Where a Marion County sample goes, and how sulfur, iron and hardness fit together in one system.
Questions
The ones people search for
Is it safe to drink water that smells like rotten eggs?
The smell itself is not the danger people assume. Hydrogen sulfide is detectable by nose at concentrations far below any level of health concern in drinking water, which is why it is classed as a nuisance rather than a health contaminant.
The caveat worth taking seriously is that a new smell can be a sign something has changed at the well, and the things that genuinely matter for health, bacteria and nitrate, have no smell at all. So a new smell is a good reason to test, just not for the reason most people think.
Why does only my hot water smell like sulfur?
The sacrificial anode rod in your water heater. It is normally magnesium, and it reacts with sulfate in the water to produce hydrogen sulfide inside the tank. Your well is not the source and your water arriving at the house is fine.
The usual fix is swapping the rod for an aluminum or zinc one. It is one part and an afternoon, and it is a plumbing job rather than a well job.
Will a water softener get rid of the rotten egg smell?
No. A softener is an ion exchange machine for calcium and magnesium and it does not remove dissolved hydrogen sulfide. If somebody has sold you one for the smell, that is what to raise with them.
What does work is aeration, an oxidizing filter, or chlorination and filtration, chosen according to how much sulfide the test shows.
The smell came on suddenly. Should I worry?
A sudden change is worth a test, where a long-standing smell mostly is not. Not because sulfide has become dangerous, but because something at the well has changed and the tests that matter for health would not announce themselves.
Test for bacteria and nitrate alongside the sulfide, and mention the timing when you send the sample. How to get that done.
Does the smell mean there is sewage in my well?
It is the fear the smell provokes and it is almost never what it is. The sulfide here comes from bacteria acting on the sulfate minerals in the limestone the aquifer sits in, which is a natural process going on underground rather than anything to do with a septic system.
That said, a bacteria test is inexpensive and it is the only thing that answers this question rather than reasoning about it. If the well is close to a drainfield, or it is shallow, or the wellhead is damaged or flooded, test rather than wonder.
Before you hire anyone
Calling a well contractor? Check three things first.
- 1The license. Every Florida water well contractor is licensed. Ask for the number and look it up at the state's contractor verification clearinghouse.
- 2The diagnosis before the price. A pressure switch reading, the tank's air charge and the cable readings, before anybody quotes a new pump. The six questions to ask.
- 3The permit, if a rig is coming. A new well needs one before drilling starts, and it is the contractor's job to have it. Who issues it.
Public offices, free to call
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