Your nose cannot tell a dried-out drain from a failing sewer line, and the fixes are nothing alike. A rotten-egg odor in the basement deserves a short round of checking before anyone assumes the worst.
This page on sewage smell Denver residents notice indoors goes from the simplest cause to the most serious, using what Denver, Aurora and health agencies publish.
Denver's wastewater FAQ answers the complaint of a foul sewer odor in the home with a dry drain. Drain pipes hold a small amount of water that seals out odors, and that seal can evaporate. The remedy it gives is to pour a little water down the drain each month.
Aurora agrees that unused fixtures dry out over time, and advises using every toilet, sink and shower and occasionally filling all floor drains. Any fixture nobody uses, a spare bathroom or a basement floor drain among them, can lose its seal that way.
Aurora describes what a failing service line looks like from inside the house: a backup of water in the lowest level, such as a floor drain, lower-level shower, tub or toilet.
A smell can also outlast a backup. Colorado's health department says that if an affected area is not cleaned and dried properly, a musty odor from continued microbial growth can remain long after the overflow. Denver's contact page lists sewer gas smells and sewer backup emergencies as two items under its Sewer Service heading, both directed to the Wastewater Management Division.
The Illinois health department, whose page is general rather than Colorado-specific, explains that "sewer gas" is hydrogen sulfide, which smells like rotten eggs at low levels. You can smell it before it makes you sick, but at higher levels the nose is overwhelmed. Dry traps are one way it enters a home.
Lower concentrations can bring eye irritation, a sore throat and cough, and the advice is to locate and eliminate the source.
A general version of this triage, not tied to Denver, is in sorting a basement sewer smell by whether the floor is wet.
When the odor is confined to the bathroom, a check of each fixture in turn narrows it to the toilet seal, a dry trap or a vent.
People who smell a drain often ask about their health; what the agencies say on breathing sewer gas separates gas from contact with sewage.
Denver's Department of Public Health and Environment enforces the city's odor ordinance and handles outdoor odor complaints from residents. It adds that odors observed beyond the city boundary generally belong to another municipality or county. An odor on your block is a separate report from a smell in your basement.
One more local culprit: Denver says several hundred storm drains are siphons, and that water left in them after storms can sit, turn stagnant and start to smell. That is the storm system, not the sanitary sewer.
Not every Denver-area sewage problem is an odor; everyday sewage trouble in Denver-area homes, from roots to flushed items covers the rest.
Aurora explains that jet-truck cleaning of a city main can pull water out of home P-traps, after which a gurgling may follow in toilets or sinks. Aurora calls this normal, says no gases from the main will be pushed into the house, and adds that traps should be kept full of water.
Water plus smell calls for the Denver sewage cleanup guide: find out whose pipe it is. Meanwhile the CDC says to wear rubber boots, rubber gloves and goggles when sewage is involved, and to keep children and pets away until cleanup is finished.
Sewage Cleanup Crew, LLC makes introductions rather than sending crews of its own, and its sewage cleanup referrals for homeowners connect people with local cleanup contractors.
A smell indoors has a short list of likely sources; indoor causes, easiest to hardest walks through traps, vents and seals.
Once the water is gone and the smell remains, removing odor after a backup explains why the source is usually something still damp.
