A sulfur filter for well water removes hydrogen sulfide, the gas behind the rotten egg smell, by oxidizing it into elemental sulfur and then filtering that out. Before buying one, find out where the smell actually comes from, because a smell that appears only in hot water is a water heater problem and no filter in the world will fix it.
Diagnose the smell before you buy anything
Run the cold tap in a bathroom well away from the kitchen and smell it after thirty seconds. Then run the hot. If only the hot smells, the cause is almost always a reaction between the magnesium anode rod in the water heater and sulfate-reducing bacteria in the tank, and the fix is an anode swap and a tank sanitization rather than a filter. If both smell and the smell is strongest at the wellhead, the sulfide is coming from the aquifer and a treatment system is the right answer. If the smell fades quickly after running, suspect bacteria in the well or the pressure tank rather than dissolved gas. Getting this right saves an entire system purchase.
Air injection oxidizing filters
The most common residential answer is an air injection filter: a tank that holds a pocket of compressed air at the top, through which incoming water falls. The oxygen converts dissolved hydrogen sulfide into solid sulfur particles, which the media bed below then catches, and the unit backwashes the accumulated solids to drain on a schedule. It needs no chemicals and no refilling, which is its great advantage over injection systems. It handles light to moderate sulfide and usually deals with iron in the same pass, which is convenient because the two very often arrive together on the same well. Sizing depends on the raw sulfide level and on your peak flow, so both numbers belong on the test report.
When you need chemical injection instead
Heavy sulfide, sulfide combined with high iron or manganese, or the presence of sulfate-reducing bacteria pushes you past what air injection can hold. That is where chlorine or peroxide injection with a retention tank comes in: a metering pump doses continuously, the retention tank provides contact time for the reaction to finish, and a backwashing carbon filter afterward removes the residual and the byproducts. It is more system to own and it needs a chemical inventory kept up, but it treats bacteria, iron and sulfur together. Our best sulfur filter for well water guide compares the two approaches against real well profiles.
The iron that usually comes with it
Iron and manganese carry secondary standards, which are aesthetic rather than health based, and Penn State Extension gives recommended maximums of 0.3 mg/L for iron and 0.05 mg/L for manganese. That matters here because a sulfur system almost always has to handle iron too, and because of one hard rule about softeners: a softener can remove dissolved iron when pH is above 6.7, hardness is between 3 and 20 grains per gallon and dissolved iron is under 5 mg/L, but oxidized iron fouls the resin. Put the oxidizing filter ahead of the softener, never behind it, or you will be cleaning resin instead of treating water.
Questions people ask about sulfur filter for well water
Why does only my hot water smell of rotten eggs?
That points to the water heater anode rod reacting with bacteria in the tank, not to sulfide in the well. Replacing the anode and sanitizing the tank is the fix.
Will a carbon filter remove sulfur smell?
A carbon cartridge helps with very light odor for a short while, then saturates. Persistent sulfide needs an oxidizing filter, not a carbon cartridge.
Does a water softener remove hydrogen sulfide?
No. A softener exchanges hardness minerals. Sulfide passes straight through, and oxidized iron carried with it will foul the resin.
Should the sulfur filter go before or after the softener?
Before. Oxidized iron and sulfur particles foul softener resin, so the oxidizing filter always comes first in the treatment train.