A rotten egg smell in house settings has four usual sources: a natural gas leak, a drain or sewer problem, a reaction inside the water heater, or hydrogen sulfide in the water supply itself, most often on wells. Rule out gas first, because utilities add that exact odor to make leaks noticeable, then use where and when the smell appears to narrow the rest. The pattern of the smell is the diagnosis.
First, rule out a gas leak
Natural gas and propane are odorized with a sulfurous compound precisely so a leak smells like rotten eggs. If the odor hangs in the air rather than arriving with running water, if it is strongest near the furnace, stove, water heater or gas meter, or if it comes and goes with no tap involved, treat it as a possible leak: leave the house without flipping switches and call the gas utility from outside. Every other cause on this page can wait a day; a gas leak cannot. Only once gas is excluded should you start diagnosing water and drains.
Smell from the drains, not the water
Fill a glass at the suspect tap and walk it to another room. If the water in the glass smells fine but the sink area stinks, the source is the drain: bacteria feeding on soap and food film in the pipe, or a dried-out P-trap in a rarely used fixture letting sewer gas seep up. Flushing the trap with water, cleaning the drain and overflow, or refreshing traps in unused bathrooms usually ends it. Persistent sewer odor across multiple rooms is worth a plumber's look at venting, since that is a plumbing fault rather than a water quality problem.
Hot water only: look at the water heater
If the smell rides only on hot water, the tank is the suspect. Inside many water heaters, the sacrificial anode rod that protects the tank from corrosion can react with sulfate in the water, especially with certain bacteria present, producing hydrogen sulfide that vents at every hot tap. The classic fix is having a plumber replace the standard magnesium anode with a different alloy and disinfecting the tank. Cold water at the same taps smelling clean is the telltale that separates this from a supply problem, so test both sides before blaming the well or the utility.
Both hot and cold: hydrogen sulfide in the supply
When every tap smells on both hot and cold, the gas is in the source water, which on a private well is your problem to solve: private wells are not federally regulated under the Safe Drinking Water Act, so no agency monitors or treats them for you. Start with a lab test to confirm hydrogen sulfide and check for the iron and sulfur bacteria that often accompany it. Treatment at the point of entry is well established, typically an oxidizing system that converts the dissolved gas into filterable particles a media bed then captures. Our whole house water filter guide covers where such a system fits in the treatment train.
Questions people ask about rotten egg smell in house
Is a rotten egg smell in the house dangerous?
It can be, which is why gas is ruled out first: utilities odorize natural gas and propane to smell exactly like rotten eggs. If the smell is in the air rather than the water, leave and call the gas company. Hydrogen sulfide in water at household levels is mainly a nuisance.
Why does only my hot water smell like rotten eggs?
That pattern points at the water heater, where the sacrificial anode rod can react with sulfate in the water and generate hydrogen sulfide inside the tank. Swapping the anode for a different alloy and disinfecting the tank is the standard fix, handled by a plumber.
How do I get rid of sulfur smell in well water?
Confirm it with a lab test first, then treat at the point of entry. Oxidizing systems that convert the dissolved gas into particles caught by a media filter are the usual answer, sized to the measured level. Testing matters because iron and bacteria often need handling too.