That rotten-egg smell is hydrogen sulfide, a dissolved gas. It's produced by sulfur-reducing bacteria in the aquifer, and in this part of the state it's common. At low levels it's a nuisance; at high levels it's corrosive to plumbing and genuinely unpleasant to live with. Iron shows up alongside it often enough that the same air-injection equipment usually treats both in one tank.
Before anyone sells you a filter, run one test yourself, right now: does the smell come from the cold water too, or only the hot?
If it's hot water only, your well is probably fine. The magnesium anode rod inside your water heater reacts with sulfate in the water and produces hydrogen sulfide inside the tank. Swapping it for an aluminum or zinc rod usually ends it — a small job, not a treatment system. Anyone who quotes you a whole-house filter without asking this question is selling rather than diagnosing.
If both hot and cold smell at every faucet, the gas is in your well water and it needs point-of-entry treatment. If it's just one fixture, it's usually bacteria in a trap or a rarely used line, not the well.
The treatment options, by concentration
| Method | Typical range |
|---|---|
| Activated carbon | < 1 ppm |
| Catalytic carbon | 1 – 3 ppm |
| Air injection (AIO) | up to ~10 ppm |
| Chlorine / peroxide | 6 ppm and up |
Air-injection oxidation is the workhorse for residential wells here. The system holds a pocket of compressed air in the top of the tank; water passing through it oxidizes the dissolved gas into a solid particle, which the media bed then catches and flushes out on backwash. No chemicals, no salt, nothing to refill. It usually handles iron and manganese in the same tank, which is why it's often the only piece of equipment a smelly well needs.
Catalytic carbon adsorbs and then oxidizes the gas. Lower maintenance than an oxidizing filter, but it needs at least 4 mg/L of dissolved oxygen in the source water to work — some wells need aeration ahead of it. Chemical injection is the right tool above roughly 10 ppm, at the cost of a feed pump to maintain and chemicals to buy forever.
Sulfur bacteria vs. dissolved gas
These are different problems with different fixes. Dissolved H₂S is a chemistry problem and gets a filter. Sulfur bacteria are a biological problem — they leave black or slimy deposits in toilet tanks and on fixtures, and they often come with a positive coliform result.
Bacteria get shock chlorination of the well first, then continuous treatment if they come back. A filter alone won't solve a bacterial colony, and a saturated carbon bed can actually become a comfortable home for one.
Sizing depends on your pump, not just your water
Backwashing filters need enough sustained flow to lift and clean the media bed — typically 5 to 12 GPM depending on tank size. If your well pump can't sustain that, an oversized filter will never backwash properly and will slowly clog. I size by the water test and the pump's sustained output, which is why I measure flow rate on the test visit.