Sewer Smell in the House? Causes, Safe Checks and When to Call

A sewer smell in the house usually means sewer gas is getting past a seal that should keep it in the pipes: a dried-out trap, a failed toilet seal, a blocked or broken vent, or a cracked drain line. In San Jose homes, a smell from one rarely used drain is often fixed by running water into it.

A smell that keeps coming back, fills several rooms or comes from under the house needs a plumber to trace it. This guide for San Jose and South Bay homeowners explains what the smell means room by room, what you can safely check, and when to call.

Safety first. Natural gas smells like rotten eggs too, because PG&E adds an odorant to it. If the smell is near a gas appliance or the meter, or you can't tell where it's coming from, leave the house without using switches or flames and call 911 and PG&E (1-800-743-5000) from outside. Sewer gas contains hydrogen sulfide, and your nose isn't a reliable gauge: CDC's ATSDR says people stop smelling it after about 2 to 15 minutes at around 100 ppm, the level NIOSH lists as immediately dangerous to life or health. If the smell is strong or anyone feels dizzy, sick or short of breath, get everyone outside and call 911. Don't go into a crawl space with standing sewage or a strong odor, and don't open a cleanout on a line that's backed up.

What Does a Sewer Smell in the House Mean?

Where you smell it is the best clue. Every fixture has a trap, a U-shaped bend that holds a plug of water between your room and the sewer, and every drain system has vents that let air in and gas out above the roof. A sewer smell means one of those barriers isn’t working, or a pipe is open where it shouldn’t be.

Checked October 2026.

Dry Traps

This is the most common cause and the easiest fix. Water in a trap slowly evaporates, so a guest bath, a shower nobody uses or a floor drain in a garage or laundry room can lose its seal in a few weeks, especially in warm weather. Run water into each drain for about a minute; pour a bucket into a floor drain. If the smell is gone in an hour or so, that was it. Run those drains every few weeks. A trap that dries out within days may be siphoning because of a venting problem, which a plumber should look at.

Toilets

A toilet sits on a wax seal over the drain flange. If the toilet rocks, the seal breaks and sewer gas, and sometimes water, gets out at the base. A smell right at the base, a damp or stained floor around it, or a toilet that moves when you sit down are the signs. Caulk around the base doesn’t fix it. The toilet has to be pulled and reset on a new seal, with the flange repaired if it’s broken. See toilet repair.

Sinks, Disposals and Washers

Not every drain smell is sewer gas. Hair, soap and toothpaste build up in a bathroom sink’s stopper and overflow, and food left in a disposal or kitchen drain smells as it decays. Clean the stopper and flush the overflow with hot water; run the disposal with plenty of cold water. A washing machine that drains into a standpipe without a working trap, or into a partly clogged line, can push sewer air back into the laundry room. If cleaning doesn’t help, the drain line beyond the trap may be partly clogged; see household drain cleaning.

Vents

Drain vents run up through the walls and out the roof. They let air in so drains flow and let sewer gas out above the house. A vent blocked by debris or a bird’s nest, a cracked vent pipe in a wall, or a failed air admittance valve under a sink can let gas into the house or siphon traps dry. Gurgling drains and a smell that’s worse on windy days or after a big flush point to venting. Leave this one to a plumber; don’t climb onto the roof to look into the vent.

Cracked or Broken Drain Lines

A drain pipe that’s cracked, has a failed joint inside a wall, or is broken under the house releases sewer gas and sometimes wastewater. Older cast-iron drains corrode from the inside, and clay sewer laterals in older South Bay neighborhoods crack and take in roots. A smell in the crawl space, along one wall, or outside near the house, especially with slow drains or soggy ground, points here. Our guides to signs you need a sewer line inspection and signs of a sewer or drain leak go further.

Hot Water That Smells Like Rotten Eggs

If the smell is in the water from the hot taps and not from the drains, it’s the water heater. Bradford White explains that the odor needs sulfur, hydrogen and bacteria, and the tank’s anode rod supplies the hydrogen. Fill one glass from the cold tap and one from the hot: if only the hot one smells, see no hot water and other water heater problems.

Is Sewer Gas Dangerous?

Sewer gas is a mix of gases from decaying waste; its rotten-egg smell is hydrogen sulfide, which ATSDR notes is often simply called sewer gas. Official sources give these numbers:

ATSDR ToxFAQs and the NIOSH Pocket Guide, checked October 2026. ATSDR also lists hydrogen sulfide as flammable.

The practical lesson is the one NIOSH gives: your sense of smell tires quickly and can’t be relied on to warn you. A faint smell that comes and goes from one drain is usually a plumbing repair, not an emergency, but a smell you’ve stopped noticing hasn’t necessarily gone away. Open windows, run the bathroom fans, and have a persistent smell traced instead of living with it.

What Can You Safely Check Yourself?

1. Rule out natural gas. If the smell is near a gas appliance or you can’t place it, leave and call 911 and PG&E.
2. Fill every trap. Run water into every sink, tub, shower and floor drain, including the ones nobody uses.
3. Check each toilet. Does it rock? Is the floor around it damp or stained?
4. Clean what’s easy to reach: sink stoppers and overflows, the disposal, and the washer’s lint filter.
5. Look outside for a sewer cleanout with a missing or broken cap, and for soggy or unusually green patches over the sewer line.
6. Compare cold and hot water to rule out the water heater.
7. Note when it’s worst: after flushing, when the washer drains, on windy days, in warm weather, or all the time. That pattern helps a plumber find it faster.

Don’t:

• pour bleach or other chemicals down drains to cover the smell: it doesn’t fix the cause, and mixing products can release harmful fumes
• seal or tape over a drain, vent or air admittance valve
• climb onto the roof to check a vent
• open a cleanout on a line that’s backed up
• crawl under the house where there’s standing sewage

How Does a Plumber Find a Sewer Smell?

A plumber starts with the traps, toilets and fixtures, then checks the drain and vent system:

• Camera inspection. A camera run through a cleanout or a pulled toilet shows cracks, failed joints, roots and breaks in the drain and sewer lines. See drain video inspection for lines inside and under the house and sewer video inspection for the lateral.
• Smoke test. Some plumbers fill the drain and vent system with harmless smoke to see where it escapes. Our plumber cost guide explains how it works.
• Fixing the cause. That might mean resetting a toilet, replacing a trap or an air admittance valve, clearing a vent, cleaning the drain or sewer line, or a spot repair or replacement of the sewer line.

CPI Service prices, October 2026. Our free sewer line inspection coupon covers a camera inspection where there’s an accessible main line cleanout.

When Is a Sewer Smell an Emergency?

Call right away, day or night, when:

• sewage is backing up into a tub, shower or floor drain (see signs of a sewer backup and signs of a clogged main sewer line)
• the smell is strong, or anyone has headaches, eye irritation, nausea or dizziness that ease when they go outside
• there’s wastewater in the crawl space or coming through a wall or ceiling
• you can’t rule out natural gas (call 911 and PG&E first)

Schedule a visit soon when the smell keeps coming back after you’ve filled the traps, a toilet rocks, drains gurgle, or the smell is outside near the sewer line.

Sewer Smells in San Jose Homes

• Older laterals and street trees. Clay and cast-iron sewer laterals in older South Bay neighborhoods crack and take in roots, which releases odor and leads to backups.
• Who owns the line. In San Jose, the property owner is responsible for the sewer lateral from the house to the City main; once an approved wye cleanout is installed at the property line, City crews repair the section from the cleanout to the main. Other South Bay cities split the line differently. See sewer lateral rules by South Bay city.
• Dry summers. Long dry spells, vacation homes and rarely used guest baths are when traps dry out.
• Buying a home. A general home inspection usually doesn’t include a sewer camera. See what a sewer scope inspection is.

Get a Sewer Smell Traced in San Jose

CPI Service finds and fixes sewer and drain odors throughout San Jose and the South Bay, with same-day service and a 24/7 emergency line. We’re licensed under CSLB License #1101278 (C-36 Plumbing), every job is quoted as a fixed price before we start, and our work carries a 1-year labor warranty. Water on the floor by the water heater is a different problem; see water heater leaking. See drain and sewer cleaning, request a free estimate or call (408) 978-3093.

Sources

• CDC/ATSDR: Hydrogen Sulfide ToxFAQs
• CDC/NIOSH: Pocket Guide to Chemical Hazards, Hydrogen Sulfide
• PG&E: Gas Safety
• Bradford White: Hydrogen Sulfide Odor / Rotten Egg Smell and Chlorinating Water Heaters

Checked October 2026.