Gas Smell Near a Water Heater: Safety Steps First

Natural gas is odorless on its own; a chemical called mercaptan is deliberately added so leaks are noticeable, producing the rotten-egg smell most people associate with a gas leak. Near a water heater, that smell can mean several different things, ranging from completely normal to a genuine emergency — and the very first thing to figure out is which one you're dealing with, since the response is completely different depending on the answer.

If the Smell Is Strong: Act Now, Don't Investigate

Evacuate everyone, including pets, immediately. Do not flip any light switches, use a phone inside, or create any spark on your way out — electrical switches specifically can ignite accumulated gas. Get to a safe distance, commonly cited as at least 350 feet from the house, and call your gas utility or 911 from there, not from inside or right next to the home.

If the Smell Is Faint: Proceed Cautiously

A faint smell allows a bit more room to investigate before evacuating outright. Turn off the gas control valve on the water heater itself — typically a lever or knob on the gas line feeding the unit, turned perpendicular to the pipe to shut it. Open windows and doors to ventilate. Then call a licensed plumber or your gas utility to inspect before using the water heater again. Don't attempt to relight a pilot light yourself once gas has been smelled, even faintly.

Not Every Rotten-Egg Smell Is Actually Gas

This is genuinely useful to know: sulfur bacteria reacting with a water heater's anode rod, especially in homes with hard water or well water, can produce a very similar rotten-egg smell — but specifically when you run hot water, not as a constant smell near the unit itself. If the odor is tied to running hot water rather than present around the tank at all times, this is a plausible and far less dangerous explanation, though it's still worth having inspected rather than assumed.

Other Non-Leak Explanations Worth Knowing

A pilot light that goes out repeatedly can release a small amount of unburned gas each time, producing a faint odor tied to a bad thermocouple or a dirty pilot tube — a real issue, but a different one from an active leak in a fitting or line. A brief whiff at startup after the unit has been off can also be normal dust or residual gas clearing, fading within a minute or two on its own.

What a Plumber Actually Checks

A technician tests fittings along the gas control valve, supply line, and pilot tubing, often with a soapy water test — bubbles forming at a fitting confirm a leak at that specific point without needing to guess. They'll also inspect the thermocouple or thermopile, check for sediment buildup affecting combustion, and verify the flue vent isn't blocked, since a blocked vent can push combustion byproducts back into the room rather than safely outside.

Prevention

A combustible gas alarm installed near the water heater, generally inexpensive, detects both natural gas and propane leaks early, often before a human would notice by smell alone. Annual professional inspection of burners, sensors, and valves, along with keeping the area around the unit clear of flammable materials, meaningfully reduces the odds of this situation happening at all.

What to Tell the Technician

Mention whether the smell was strong or faint, whether it's constant or only noticeable when hot water runs, how long it's been happening, and the age of your water heater. This context helps a technician prioritize your call correctly and arrive already narrowing between the more likely explanations rather than starting from a completely blank slate.

The One Rule That Doesn't Change

Regardless of which explanation turns out to be correct, don't turn the gas back on or attempt to use the water heater again until it's been properly inspected and, if needed, repaired. Guessing wrong here isn't a minor mistake.

Sources: Water Heater Checker, Kimco.