Narrowing it down once gas is ruled out
These patterns only apply after a gas leak has been ruled out by the utility or a qualified professional.
- IfThe smell appears only when hot water runs, and cold water is fineThenThe water heater is the likely source. Sulfate in the water can react with the tank's anode rod and produce hydrogen sulfide.
- IfBoth hot and cold water smell when first runThenThe water supply or the plumbing near the meter may be involved. Contact the water provider listed on your bill.
- IfThe smell is strongest near a basement floor drain, a rarely used shower or a laundry standpipeThenA trap has probably dried out and sewer gas is coming up. Running water into it is the first test.
- IfThe smell is near a toilet base, especially a basement toiletThenA failed wax ring or loose toilet can let sewer gas escape. A plumber can reset it.
- IfThe smell comes and goes with wind or weatherThenA plumbing vent may be blocked or too close to a window or air intake. Have the vent stack checked.
How the three sources usually differ
| Clue | Gas leak | Sewer gas | Water heater reaction |
|---|---|---|---|
| Where it is strongest | Near the meter, furnace, range, water heater burner or fireplace | Near drains, toilets, sump area or unused fixtures | At hot water taps and the shower |
| When it happens | Any time, often constant | Often after a fixture sits unused | When hot water runs, often worse after vacation |
| Who to call | 911 or the gas utility, from outside | A plumber | A plumber or water heater technician |
| Can you investigate yourself? | No | Yes, by filling traps with water | Yes, by comparing hot and cold taps |
Why this shows up around a move
Homes that sit empty during a sale are prime candidates for the two non-emergency causes. A basement bath that nobody used for months loses the water seal in its trap through evaporation, which happens quickly in Colorado's dry indoor air during heating season. Water heaters that sit unused allow the water in the tank to stagnate, and the sulfur reaction tends to be most noticeable the first time someone runs a hot shower after move-in.
For the water heater version, plumbers sometimes replace the anode rod with a different alloy, flush the tank, or adjust the temperature setting. Which option fits depends on the heater, its age and the manufacturer's instructions, so it is a job to talk through with a plumber rather than improvise. For sewer gas, the fix may be as simple as running water into each fixture once a month, though a trap that keeps drying out may point to a venting problem.
Simple non-emergency checks
- Run hot and cold water separately at the same sink and compare the smell
- Pour water into every floor drain, unused shower and basement sink
- Run a full cycle in the washing machine if the standpipe area smells
- Check that every toilet is firmly set and does not rock
- Note whether the smell started after a stretch of vacancy or travel
General information for Highlands Ranch, not a quote or professional advice. In an emergency, call 911.