Your Cart is Empty
Why Does My Water Smell Like Rotten Eggs? (And How to Fix It)
A rotten-egg smell from your tap is hydrogen sulfide gas, and it has three common sources: your water heater, your well, or a drain. The good news is that a two-minute test tells you which one you have, and two of the three are cheap to fix. Here's how to tell them apart and what to do about each.
Step one: is it hot water, cold water, or one sink?
Fill a glass from the cold tap at the kitchen sink after running it for a minute, and smell it. Then do the same from the hot tap. Then try a different sink.
- Hot water only → the water heater. This is the most common case in homes on city water and on wells alike.
- Hot and cold, every tap → hydrogen sulfide in the supply, almost always a private well.
- One sink only, or only when water first runs → bacteria in the drain trap or a dead-end pipe run, not the water.
If only the hot water smells like rotten eggs
Water heaters have a sacrificial anode rod, usually magnesium, that corrodes so the tank doesn't. Sulfate-reducing bacteria in the tank use the hydrogen the rod gives off and produce hydrogen sulfide. The water coming into the house is fine; the heater is making the smell.
The fix, in order of effort:
- Replace the anode rod with an aluminum-zinc rod or a powered (impressed-current) anode. This is the permanent fix and costs $30–$150 in parts. Do not simply remove the rod; the tank will rust out.
- Flush and disinfect the heater. Drain the tank, refill with a cup of 3% hydrogen peroxide per 10 gallons, let it sit two hours, then flush. This clears the existing bacteria; without the anode change it usually comes back.
- Turn the heater up to 160°F for a few hours to kill the bacteria, then back down. A temporary measure only, and scald-risky.
Tankless heaters rarely have this problem because they have no anode and no stored water.
If every tap smells: hydrogen sulfide in well water
When the cold water smells too, the gas is in the water arriving from the well. It comes either from sulfur bacteria living in the well and plumbing, or from groundwater passing through sulfur-bearing rock, shale or coal seams. Both are common across the Midwest, the Great Lakes states, Texas and Florida. At the concentrations found in wells hydrogen sulfide is a nuisance rather than a health hazard, but it corrodes copper and steel, tarnishes silverware, stains fixtures black, and usually travels with iron and manganese that stain everything orange and brown.
Get the number first
Fixing it correctly depends on how much H₂S is in the water, in ppm (mg/L), and whether iron and manganese are present. Hydrogen sulfide gasses off within hours, so a sample mailed to a lab often reads low; ask for a field test, or a lab kit with a preservative, and have iron, manganese, pH and hardness run at the same time. A basic panel is $30–$150.
The fixes, by concentration
| H₂S level | What works | What it costs |
|---|---|---|
| Bacterial, recent onset | Shock-chlorinate the well (pour, circulate, let sit 12–24 hours, flush). Clears the smell for weeks to months; repeat or filter if it returns. | $20 of bleach and an afternoon |
| Trace, under 1 ppm, no iron | A catalytic carbon filter. Simple, but the media exhausts fast above this level. | $1,000–$1,300 |
| Up to about 5 ppm, with or without iron | An air-injection (AIO) filter. A single tank traps an air pocket; oxygen oxidizes the H₂S to solid sulfur and iron to rust, the media catches both, and a nightly backwash flushes it to drain. No chemicals. This is the standard fix. | $1,300–$2,000 |
| Above 5–6 ppm, or bacteria that keep returning | Chlorine injection with a retention tank, followed by a backwashing carbon filter to remove the chlorine and the precipitate. | $4,500–$6,000 for the set |
The filter goes after the pressure tank and before any water softener, because sulfur and iron foul softener resin. A softener on its own will not remove the smell; neither will an ordinary whole-house carbon filter once the level is above a trace.
Our sulfur filters for well water collection lists the air-injection, Katalox Light and chlorination systems by H₂S level, on both Clack and Fleck valves, with the sizing rule that matters: the tank has to backwash at your well pump's flow rate (about 5 GPM for a 10″ tank, 7 GPM for 12″, 10 GPM for 13″), or the media never cleans and the smell comes back.
If it's one sink or the drain
Bacteria growing in a drain trap, a garbage disposal or an overflow channel give off the same gas, and the smell wafts up when you run water. Pour a cup of baking soda followed by a cup of white vinegar down the drain, wait ten minutes, flush with hot water; clean the disposal and the overflow. If the smell is only when water first runs after a long idle period, flush the line and it clears.
What about city water?
Municipal water is chlorinated, so hydrogen sulfide in the supply is rare. A rotten-egg smell on city water is almost always the water heater anode or a drain. If the whole house smells on cold water, call the utility; it can indicate a main break or a treatment problem.
Quick reference
- Hot only → anode rod. Replace with aluminum-zinc or powered.
- Hot and cold, well → test for H₂S, iron, manganese; AIO filter up to ~5 ppm, chlorination above.
- One sink → drain trap. Clean it.
- New smell after well work or flooding → shock-chlorinate; filter if it returns.
Not sure which you have? Call 800-374-2143 with your test results and we'll tell you whether you need a filter at all, and which one if you do. See also: iron filters and well water filtration systems.
Leave a comment
Comments will be approved before showing up.
