Why the Well
If your well water smells like rotten eggs, check hot vs cold before you buy a filter.
The smell is hydrogen sulfide. Where it shows up tells you whether the problem is the water heater or the well.
Most people skip this step and waste a few hundred dollars. Two faucets. Then you stop guessing.
Do this first (two minutes)
- Leave the house for a couple of hours if you can. Your nose gets used to the smell fast.
- Run cold water in a bathroom or kitchen that is not right next to the water heater. Smell it.
- Run hot water from the same tap. Smell it.
If only the hot water stinks
The well is probably fine. A common cause is the sacrificial anode rod inside the water heater. A magnesium rod can react with sulfate in the water and make hydrogen sulfide when the tank heats. State health departments say this all the time. Replace that rod with aluminum or aluminum/zinc, or have a plumber do it. Flush the tank. Do not buy a whole-house sulfur filter for a heater problem.
Gas water heater, or you cannot see the rod? That is a plumber job.
If cold water stinks too
The gas is in the well or the plumbing. It can be hydrogen sulfide in the groundwater, or sulfur bacteria making slime. Black stains, or gunk in the toilet tank, lean toward bacteria.
Do not guess the number from your nose. Test for hydrogen sulfide, iron, manganese, pH, and hardness. County extension or a well-water lab. A strip is a start, not a design spec for a big tank.
After a test, people usually land here:
- Small smell, no bacteria: carbon can knock it down. Media dies. Budget to replace it.
- Sulfur plus iron: an oxidizing / air-injection style iron filter is the usual whole-house answer when the lab says so.
- Bacteria in the well: shock chlorination, sometimes a well contractor if slime is bad. A filter without cleaning the well is a mop on a running tap.
What not to buy
- A softener. Softeners treat hardness. Wrong tool for rotten egg.
- The most expensive “well system” bundle because an ad said sulfur.
Sudden new smell after a flood, a dry well, or work on the cap can be a sanitary issue. Call a licensed well person.
If you actually need a box
Hot water only: an aluminum-zinc anode rod is the usual swap for a magnesium rod. Gas heater, or you cannot see the rod, is a plumber job. Do not buy a sulfur tank for the heater.
Cold water too: a strip is a start, not a design spec. These hydrogen sulfide test strips are that start. The Watersafe well water test kit covers iron, hardness, pH, and copper so you do not buy two wrong machines. A home bacteria vial is not a health-department coliform test after a flood.