Why your well water smells like rotten eggs
That smell is hydrogen sulfide. It's a gas, it's dissolved in your water, and at the concentrations that show up in a house it's a nuisance rather than an emergency, which is the first thing worth knowing, because the smell is alarming enough that most people assume the worst.
The second thing worth knowing is that there are two completely different causes, one of which costs a few hundred dollars to fix and one of which doesn't.
The 30-second test
Run the cold tap. Let it go for a minute. Smell it. Then run the hot tap. Same thing.
Cold water is fine, only the hot smells → it's almost certainly your water heater, not your well.
Both smell → the hydrogen sulfide is coming in with the water, and it's a whole-house issue.
Only one fixture smells → check that fixture's aerator and drain before anything else. Sometimes the smell is in the drain, not the water, and you can prove it by filling a glass and walking into another room with it.
Do this before you call anybody, including us.
If it's only the hot water
Your water heater has a sacrificial anode rod, a metal rod inside the tank that corrodes on purpose so the tank doesn't. On most heaters it's magnesium.
In water containing certain naturally occurring sulfate-reducing bacteria, the reaction at that magnesium rod produces hydrogen sulfide. The bacteria are harmless. The rod is doing its job. The combination smells like a swamp.
The usual fixes, in order of how often they work:
- Replace the magnesium anode with an aluminum/zinc alloy rod. Common, inexpensive, and it solves it most of the time.
- Flush and disinfect the tank. Sometimes enough on its own, sometimes buys time.
- Remove the anode entirely, we're including it because you'll read it online. Don't. It voids most tank warranties and trades a smell for a shorter tank life.
This is a plumber's job, or a competent homeowner's Saturday. It is not a water treatment job, and we're not going to sell you a system for it. If that's what your test showed, you now have what you came for.
If it's the cold water too
Then the hydrogen sulfide is in the well, and it's a treatment question.
How it's handled depends on how much there is, which is the whole reason the smell test isn't the end of the process. Low concentrations, moderate concentrations, and high concentrations get genuinely different equipment, and a system sized for the wrong one either doesn't work or costs more than it needed to.
The approaches, broadly:
- Oxidation and filtration, the sulfide is converted and then filtered out. The most common answer at typical residential concentrations, and it comes in several forms depending on the number.
- Aeration, physically strips the gas out of the water before it enters the house. Effective at higher concentrations; more equipment and more space.
- Carbon filtration, works at genuinely low levels. Undersized for anything more, and this is the mistake that shows up most often in houses that already have something installed and still smell.
A softener does not remove hydrogen sulfide. If you have a softener and the smell is still there, the softener isn't broken and isn't the answer, it was never the right tool for this.
The reason we test before we quote
A sulfur smell rarely travels alone.
The same water chemistry that produces hydrogen sulfide often comes with iron, manganese, or both, and iron in particular changes what equipment is appropriate, because some sulfide treatments are affected by iron and some iron treatments handle sulfide as a side effect. Getting the sequence wrong produces a system that works for six months.
And separately: the smell is the thing you noticed, but it isn't necessarily the most important thing in the water. Arsenic, uranium, and nitrate occur naturally in parts of this region's aquifer and none of them smell like anything at all. If we're going to send a sample to a lab anyway, testing for the things you can't detect costs almost nothing extra and is the actual point.
What we'd do
A free consult first. Twenty minutes on the phone. We'll walk the hot-versus-cold test with you if you haven't done it, ask what your well is, and tell you honestly which of the two problems you likely have.
If it's the water heater, we'll say so and you'll be off the phone in ten minutes having spent nothing.
If it's the well, the Water Assessment is a paid certified lab panel that measures the sulfide alongside everything else, credited in full toward a system if you go ahead.