Key facts: Emergency Sewer Gas Smell
- Sewer gas can contain hydrogen sulfide, ammonia and methane, and the rotten-egg note usually signals hydrogen sulfide [1].
- Hydrogen sulfide is flammable, slightly denser than air, and quickly deadens the sense of smell at higher levels [2].
- A dried-out trap in a rarely used fixture is the most common way sewer gas enters a building, especially in warm weather [1].
- Plumbing vents carry sewer gas outdoors; a blocked vent can pull water out of traps [1][3].
Why this page is different
When a sewer odor turns into an urgent problem
A faint whiff from a guest bathroom that fades after you run the tap is a routine nuisance, and the site's guides cover it. This page is about something else: a smell that is strong, spreading into several rooms, getting worse, or coming with headaches, nausea or a hissing or wet sound inside a wall.
Sewer gas is a mix of gases from decomposing waste. In a well-vented home it is mostly ordinary air with some methane, which is why a small leak is unpleasant but rarely dangerous [1]. The trouble starts when a lot of it escapes indoors. Hydrogen sulfide, the source of the rotten-egg note, irritates the eyes and airways at low levels, and both it and methane can ignite from a spark [1][2].
There's a trap here too, and not the plumbing kind. Hydrogen sulfide tires out your nose quickly, so a smell that seems to fade after a few minutes may simply mean you have stopped noticing it [2]. Judge by how strong it was when you walked in, not by how it seems now.
Warning signs
Odor clues that point to an urgent cause
Smell in several rooms at once
One dry trap rarely fills a whole house. A broken drain or vent pipe, or a failed toilet seal, is more likely.
Smell plus a wet wall or ceiling stain
A cracked drain or vent pipe inside a wall can leak both water and gas into the cavity.
Smell plus gurgling in every drain
The line or vent may be blocked, pushing air and gas back through traps [3].
Smell strongest at the toilet base
The wax ring or flange may have failed, especially if the toilet rocks.
Headache or dizziness while indoors
Treat this as a health issue first; get outside and call for medical advice.
Safe immediate steps
Finding the source without making it worse
Once the house is ventilated and natural gas is ruled out, these checks are low risk.
- 1
Walk the house with fresh air behind you
Step outside for a few minutes, then come back in and note which room hits you first. Your nose resets outdoors.
- 2
Refill every trap you can find
Run water for a short while in spare sinks, tubs and showers, and pour a pitcher into any floor drain in the garage or laundry. A seal that dried out in the heat often explains a sudden smell [1].
- 3
Check toilets for movement
Gently push each toilet side to side. A toilet that shifts, or has a damp ring at its base, may have a broken seal.
- 4
Look under sinks
A loose slip nut or a trap knocked off its tailpiece leaves an open pipe straight to the sewer under the cabinet.
- 5
Note what you found
Write down where the smell is strongest and what changed recently: remodeling, a new appliance, a trip away, a storm.
What not to do
Mistakes that make a sewer odor more dangerous
- Masking it with candles or spraysAn open flame near a strong sewer-gas pocket is a real risk, since both methane and hydrogen sulfide burn [1][2].
- Pouring bleach and drain cleaner togetherMixing drain products can release harmful fumes on top of the odor you already have [4].
- Climbing onto the roof to clear a ventRoof work on steep tile is a fall hazard. Leave vent clearing to the contractor.
- Opening a cleanout cap indoorsIf the line is backed up, a cap can release sewage and a burst of gas into the room.
- Ignoring it because the smell fadedYour nose adapts. A smell that seemed to vanish may still be there [2].
When to call
Odor signs that mean calling now
- The odor is still strong after every trap has been refilled and the house has aired out.
- You can hear water or air moving inside a wall, or a stain is growing.
- Drains gurgle or bubble while the smell is present.
- A toilet rocks or water seeps from its base.
- The smell keeps returning within hours of airing the house.
The visit
How does a contractor track down a sewer gas leak?
The independent contractor will usually start where you did, confirming that traps hold water and toilets are sealed. From there, the common tools are a sewer camera run through a cleanout or pulled toilet to look for cracked or separated joints, and a smoke test, where harmless theatrical smoke is pushed into the drain system and watched for where it escapes. You can read about the camera side on the drain camera inspection page.
If the vent is blocked, the contractor may clear it from the roof or from a cleanout. If a pipe inside a wall is broken, they will explain what opening the wall involves. Where the smell is tied to a backed-up main line, the job becomes a drain clearing first, and the emergency drain cleaning page covers that.
Ask the contractor to show you any camera footage and to tell you whether the fix is the trap, the seal, the vent or the line itself. That record helps if the odor returns.
Henderson factors
Why desert heat drives so many odor calls here
Henderson's summers are long and hot, with July highs averaging around the low hundreds Fahrenheit and very little rain across the year [5]. A trap seal is just a small pool of water, and in a closed-up spare bathroom or a garage floor drain next to a water heater, it can evaporate in a matter of weeks. Floor drains near water heaters are a known weak spot for exactly this reason [1].
Many homes here are single-story, slab-built houses with spare baths that see little use, and a good number belong to owners who spend part of the year elsewhere. The second home drain backup page covers what to check when you return. For the planned, non-urgent side of rarely used fixtures, read the guide to dry p-traps in unused bathrooms.
If the odor seems to come from outside, near the street, and neighbors notice it too, the source may be the public sewer. Henderson Utility Services handles the city side [6]. See all urgent topics on the emergency hub.
FAQ
Sewer gas smell questions Henderson residents ask
Answers about urgent sewer odors; more on the [questions hub](/faq/). Back to [all emergency topics](/emergency/).
How do I know if it's sewer gas or a natural gas leak?
You often can't be certain by smell alone, because both can seem like rotten eggs. Natural gas has an added odorant, while sewer gas gets its smell mostly from hydrogen sulfide [2]. If there's any doubt, leave the house and call the gas utility from outside before treating it as a drain problem.
Can breathing sewer gas in my house make me sick?
Low levels of sewer gas mostly cause irritation, but longer exposure can bring headaches, fatigue and dizziness, and high hydrogen sulfide levels are dangerous [1]. Most household odors stay at nuisance level. If anyone feels unwell, get outside, ventilate, and seek medical advice before investigating further.
Why did the sewer smell suddenly fill the whole house overnight?
A whole-house odor that appears overnight often means something changed in the drain or vent system, not just one dry trap. A blocked vent can pull water out of several traps [3], and a cracked pipe or failed toilet seal can leak gas into rooms. Refill traps first, then call if it persists.
Is it safe to sleep in a house that smells like sewage?
Sleeping there is reasonable only if the smell is faint, the house is aired out and nobody has symptoms. If the odor is strong, spreading or causing headaches, stay elsewhere until the source is found. Remember that hydrogen sulfide can dull your sense of smell, so a fading odor isn't proof it's gone [2].
Can a blocked roof vent cause a rotten egg smell inside?
A blocked roof vent can cause indoor odors, because drains lose the air supply that keeps trap seals in place [3]. Water gets pulled out of traps and sewer gas follows. Gurgling drains alongside the smell are a common clue. Clearing a vent on a steep tile roof is a job for the contractor, not a ladder at night.
What should I tell the drain company about a sewer odor?
Describe where the smell is strongest, when it started and whether it comes and goes. Mention any gurgling, wet stains, a rocking toilet, recent remodeling or time away from the house. Say whether you have refilled the traps already. Those details help the contractor decide between a camera, a smoke test or vent work.
Who handles a sewer smell coming from the street in Henderson?
A smell coming from a street manhole or shared by several neighbors may be on the public side, which the City of Henderson maintains. Contact Henderson Utility Services through its customer care center [6]. If the odor is inside your home only, the source is usually in your own drains, vents or lateral.