Why Does My Water Smell Like Rotten Eggs?

A rotten-egg smell in your water almost always comes from hydrogen sulfide, a gas produced by bacteria reacting with sulfur compounds. The fix is usually simple — but which fix depends entirely on where the smell shows up, and you can diagnose that in 30 seconds.

Quick diagnosis: Run the hot water at one faucet for 30 seconds and smell it. Then run the cold water and smell that. Smell only in the hot water? Your water heater’s anode rod is reacting with naturally occurring sulfates — this is the most common cause, and the fix costs about $30. Smell in both hot and cold? Sulfur bacteria are in your water supply, most likely a private well. Smell at only one faucet? The bacteria are living in that faucet’s aerator or drain, not in your water at all.

Before anything else, one urgent exception: if the rotten-egg smell is strong near a gas appliance, furnace, or stove, leave the house immediately. That could be mercaptan — the chemical gas companies add to natural gas — which means a gas leak, not a water problem. Call 911 or your gas utility from outside. A water smell issue, by contrast, smells strongest at the tap, and the fix is a DIY job.

Hydrogen sulfide in household water: what it is

Hydrogen sulfide (H₂S) is a colorless gas that smells like rotten eggs even at very low concentrations. In household plumbing it comes from one of two sources:

1. Sulfur bacteria — harmless microorganisms that live in water and feed on sulfate, producing hydrogen sulfide as a byproduct. They thrive in low-oxygen environments like water heaters and wells.
2. Chemical reaction — the magnesium anode rod inside your water heater can react directly with sulfate in the water to create hydrogen sulfide, even without much bacterial involvement.

At household levels, hydrogen sulfide is a nuisance, not a health hazard. You can smell it at concentrations far below anything that would harm you. It can corrode metal pipes and fixtures over time and turn water slightly gray, but it won’t poison you from your tap. That said, if the smell appeared suddenly and is very strong, a water test is a sensible confirmation.

The 30-second diagnosis

Do this test before buying anything: run the hot water at the faucet closest to the water heater for 30 seconds, fill a glass, and smell it. Repeat with the cold water, then check a second faucet (a bathroom tap, ideally).

Only hot water smells → the water heater anode rod. The magnesium anode rod inside the tank reacts with sulfates in your water supply. This is the single most common cause of rotten-egg smell in homes on city water. The fix is a ~$30 aluminum/zinc anode rod swap (details below).

Hot and cold both smell → sulfur bacteria in the supply. If you’re on a private well, bacteria are living in the well or the plumbing system. If you’re on city water and both hot and cold smell, the bacteria are in your home’s plumbing or the water heater — flush the heater first, and if the cold water still smells, shock-chlorinate the well or call your water utility.

Only one faucet smells → fixture bacteria. Bacteria are living in that faucet’s aerator or drain, not in your water. Remove and clean the aerator and scrub the drain — a 10-minute fix.

No smell at any faucet, but neighbors smell it too → municipal supply. Call your water utility — they may be flushing mains or dealing with a source-water issue.

Fix 1: Replace the anode rod (~$30, the most common fix)

The anode rod is a metal rod inside your water heater that sacrifices itself to prevent tank corrosion. The standard magnesium rod reacts with sulfate in the water to produce hydrogen sulfide. Swapping it for an aluminum/zinc alloy rod stops the reaction in most cases.

You’ll need: an aluminum/zinc anode rod (about $25–$35 at any hardware store — measure your heater’s height or check the manual for the correct length), a 1-1/16" socket, a breaker bar or long ratchet, Teflon tape, and a helper to hold the heater steady.

1. Turn off the water heater — flip the breaker for electric, or set gas to pilot. Shut off the cold inlet valve.
2. Relieve pressure — open a hot faucet in the house and pull the T&P relief valve lever briefly.
3. Drain a few gallons into a bucket, enough to drop the water level below the rod’s top fitting.
4. Unscrew the old rod from the top of the heater (usually under a hex-head cap). Factory-installed rods are tight — have a helper brace the heater so it doesn’t twist.
5. Wrap the new rod’s threads with Teflon tape, thread it in, and tighten firmly.
6. Refill the tank, close the faucet, restore power or gas, and check for leaks around the new fitting.

If your heater is older than 10–12 years, weigh a rod replacement against a new unit. For more on water heater behavior, see Why Is My Water Heater Making Noise?.

Fix 2: Flush the water heater

Sediment and bacteria accumulate at the bottom of the tank, feeding the smell. Flushing removes them:

1. Turn off power/gas to the heater and shut off the cold inlet valve.
2. Attach a garden hose to the drain valve and run it to a floor drain or outside (the water will be hot and dirty).
3. Open a hot water faucet in the house to let air in.
4. Open the drain valve and let the tank drain completely — stir up sediment by briefly opening and closing the cold inlet a few times while draining.
5. Close the drain valve, refill the tank, restore power/gas.

Do this once a year as routine maintenance. It’s the cheapest prevention there is.

Fix 3: Raise the temperature to 140°F briefly

Sulfur bacteria die at 140°F (60°C). If your heater is set to the standard 120°F, bacteria can survive inside it:

1. Turn the thermostat up to 140°F for 2–3 hours, running each hot water faucet briefly to circulate the hot water through the pipes.
2. Turn it back down to 120°F afterward. Water at 140°F can scald in seconds — this is especially dangerous for children and older adults. Never leave the heater at 140°F permanently unless you have a thermostatic mixing valve installed.

Fix 4: Shock-chlorinate a well (well owners)

If you have a private well and both hot and cold water smell, the bacteria live in the well itself. Shock chlorination — a measured dose of unscented household bleach added to the well and run through the system, left 12–24 hours, then flushed until no chlorine smell remains — kills them. Well construction varies, so follow your state extension service’s guide for your well type and retest afterward.

What you’ll need

• Aluminum/zinc alloy anode rod (~$25–$35)
• 1-1/16" socket, breaker bar, Teflon tape
• Garden hose and bucket (for flushing)
• White vinegar and an old toothbrush (for cleaning faucet aerators)
• Unscented household bleach (well chlorination only)
• A drinking-water test kit or lab test if you want confirmation (~$15–$30 for a basic kit)

Cost estimates

Safety warnings

• Rotten-egg smell near a gas appliance is an emergency. Mercaptan, the odorant added to natural gas, smells like rotten eggs. If the smell is strongest near the furnace, stove, or gas line — not at the tap — get everyone out of the house, don’t flip switches or use phones inside, and call 911 or your gas utility from outside.
• Hydrogen sulfide at household water levels is a nuisance, not a poisoning risk. But if the smell is suddenly overwhelming, or you’re on a well and the smell appeared overnight, test the water before assuming it’s the usual benign cause.
• Scald risk at 140°F. When you raise the heater temperature to kill bacteria, keep it there only 2–3 hours and turn it back to 120°F. Water at 140°F causes third-degree burns in seconds.
• Turn off power/gas before servicing the water heater. An electric heater with a drained tank and live power will burn out its elements in minutes. For gas, follow the manufacturer’s relighting instructions exactly.
• Don’t drink heavily chlorinated water during well treatment. Flush the system until the chlorine smell is completely gone.

Frequently asked questions

Is sulfur-smelling water safe to drink? At typical household levels, yes — hydrogen sulfide is detectable by smell far below health concern levels. But if the smell appeared suddenly and strongly, or you have a private well, get the water tested to rule out other contamination.

Why does only the hot water smell? Because the source is inside the water heater. The magnesium anode rod reacts with sulfates in the water to produce hydrogen sulfide gas, which is released when hot water flows. Swapping the magnesium rod for an aluminum/zinc alloy rod fixes it in the vast majority of cases.

Why does the smell come and go? Bacteria activity varies with temperature and water usage. It’s often strongest first thing in the morning or after the house sits unused for days, because hydrogen sulfide builds up in stagnant water overnight.

Can I just remove the anode rod instead of replacing it? Removing it stops the smell but voids most tank warranties and shortens the tank’s life — the rod prevents the steel tank from corroding. The aluminum/zinc rod is the right fix: it stops the reaction while still protecting the tank.

Does a water softener cause the rotten-egg smell? The softener doesn’t create it, but its resin bed can harbor sulfur bacteria, and softened water can make an anode-rod reaction more noticeable. If the smell started after installing one, sanitize the softener per the manufacturer’s instructions and check the anode rod.

How long does the smell take to go away after fixing the anode rod? Usually within a day of hot water use — the trapped gas flushes out quickly once the source is gone. Run each hot faucet for a few minutes. If the smell persists beyond 48 hours, the bacteria are in the plumbing or well, and you’ll need the deeper fixes above.

Prevention tips

• Flush the water heater annually to clear sediment where bacteria colonize.
• If your water has high sulfate content, install an aluminum/zinc anode rod proactively instead of waiting for the smell.
• Run rarely used faucets weekly — stagnant water breeds bacteria.
• Clean faucet aerators every few months; they’re bacterial hotspots.
• Well owners: test water annually and sanitize the well system if bacteria counts rise.
• Keep the water heater at 120°F normally — hot enough to discourage most bacteria, cool enough to prevent scalding.

When to call a pro

• The smell is strong near a gas appliance or you smell gas — leave the house and call 911 or your gas utility from outside. This is an emergency, not a plumbing call.
• Hot and cold water both smell on city water and flushing the heater didn’t fix it — you may need professional disinfection of the home plumbing.
• Well water smells after shock chlorination — the well may need professional treatment or inspection for a failing casing.
• The water heater is over 10 years old and the rod is seized or the tank shows rust — replacement may be the smarter move.
• The anode rod hex fitting won’t budge and the heater is twisting — forcing it can break pipes; a plumber has the tools and leverage.
• Water tests show contamination beyond sulfur (coliform, nitrates, heavy metals) — these need professional treatment systems.