A sulphur smell in well water is hydrogen sulfide gas, and it reaches the tap by one of three routes: dissolved in the groundwater, produced by bacteria in the well or the plumbing, or generated inside the water heater. Each has a different fix and the wrong equipment is a common and expensive mistake, so identifying the route comes first.
Three checks that identify the source
Smell the cold water and the hot water separately at more than one fixture. Hot only means the water heater, where sulfate reducing bacteria interact with the sacrificial anode rod, and the fix is at the appliance rather than the water. Both hot and cold means the supply. Then look for slime: a dark, slippery film in the toilet cistern or on fixtures that reforms within days of cleaning points at sulfur bacteria, which need disinfection as well as filtration because they regrow from whatever survives.
Oxidize then filter, the standard approach
For dissolved hydrogen sulfide in the water, treatment means converting the gas to elemental sulfur particles and filtering those out. Air injection systems draw a pocket of air into the top of a vessel and pass water through it before a catalytic media bed. Chemical feed systems dose an oxidant ahead of a retention tank and a filter, which handles heavier loads and deals with bacteria at the same time. Manganese greensand and similar media oxidize and filter in one vessel, regenerated on a schedule.
Aeration, and where it suits
Aeration systems strip the gas out of the water by exposing it to air in a vented tank, then repressurise the treated water for the house. They use no chemicals and no media that needs regenerating, they handle high sulfide loads well, and the smell leaves with the vent rather than being converted into something to filter. In exchange they need space, a vent to outside, and a pump, and they introduce oxygen which can precipitate iron, so the arrangement usually includes a filter behind them.
Sizing from a test, not from the smell
Hydrogen sulfide is detectable by smell at concentrations far below those that need aggressive treatment, so nose alone is a poor guide to equipment size. The EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, which makes a laboratory test the owner's own responsibility and the only sound basis for specifying. Test for sulfide, iron, manganese and pH together, since the treatment interacts with all of them. Our whole house filter guide covers ordering the stages.
Questions people ask about sulphur water filter
Why does only my hot water smell?
The hydrogen sulfide is being produced inside the water heater by bacteria interacting with the anode rod. The fix is at the appliance.
What if there is slime as well as smell?
That points at sulfur bacteria, which need disinfection alongside filtration because they regrow from whatever the filter leaves behind.
Is aeration better than an oxidizing filter?
It handles heavy loads well and uses no chemicals, but it needs space, a vent and a pump, and it usually needs a filter behind it for precipitated iron.
Can I size the system by how strong the smell is?
No. Sulfide is detectable well below the levels that decide equipment size, so a laboratory test is the only sound basis.