Clearing a rotten egg smell permanently means treating the right thing, and the three sources need completely different work. Two of the checks that tell them apart cost nothing and take minutes, which makes doing them first the most valuable step in the whole job.
Step one: find where it is coming from
Smell the cold and hot taps separately at two fixtures well apart. Hot only means the water heater is producing the gas, where bacteria interact with the sacrificial anode rod, and the supply itself is fine. Both means the water carries it. Then look in the toilet cistern: a dark slippery film that returns within days of cleaning points at sulfur bacteria living in the well, while clear water with a smell and no film points at dissolved hydrogen sulfide, which is chemistry rather than biology.
Step two, if it is the heater
Raise the heater to the disinfection temperature the manufacturer permits, following their instructions and being careful about scald risk afterwards, then flush the tank thoroughly to carry out the sediment the bacteria live in. If the smell returns, replace the magnesium anode rod with an aluminium zinc alloy rod, which very often ends it permanently. Removing the anode entirely is not the answer, because the tank then corrodes. This whole job costs a fraction of any water treatment system.
Step three, if it is the well
Bacteria need disinfection, so shock chlorinate the well and plumbing, then retest after normal use resumes and again some weeks later. A shock that holds for a few weeks and then fails means the organisms are re-establishing and continuous chlorination is the durable answer. Dissolved sulfide needs oxidation and filtration: catalytic carbon for light loads, an air injection system with catalytic media for moderate ones, greensand type media where iron and manganese are present too, or chemical feed for heavy loads.
Step four: size it from a test, not the smell
Hydrogen sulfide is detectable by nose far below the levels that decide equipment size, so a strong smell does not mean a heavy load and the reverse is also true. The EPA notes private wells are not federally regulated under the Safe Drinking Water Act, so a laboratory test is both your responsibility and the only sound basis for specifying. Test sulfide alongside iron, manganese and pH, since the treatment interacts with all three. Our sulfur filter guide covers matching media to a measured level.
Questions people ask about how to get sulfur smell out of well water
How do I tell if it is the water heater?
Smell the hot and cold taps separately at two fixtures. Hot only means the heater is producing the gas and the supply is fine.
What if the smell keeps coming back after shocking the well?
The bacteria are re-establishing, which usually means continuous chlorination rather than repeated shocks.
Should I remove the water heater's anode rod?
No. It protects the tank from corroding. Replace magnesium with an aluminium zinc alloy rod instead.
Can I size treatment from how strong the smell is?
No. Sulfide is detectable well below the levels that decide equipment size, so a laboratory test is what sizes the system.