The short answer
What Causes the Smell
Heavy rain can push water through cracks in your foundation, around window wells, or through a floor drain that overflows. That water soaks into drywall, carpet, and concrete, and the dampness lets mold and mildew multiply. Mold releases musty gases, which is the smell you notice.
Another possible source is a sewer backup. If the municipal drain system gets overwhelmed, sewage can back up into basement floor drains. That brings a strong, unpleasant odor that is different from a damp smell. You might also notice staining or moisture along baseboards.
Check for Standing Water
First, look for puddles, damp spots, or wet materials. If you see standing water, do not walk through it if it might contain sewage. Turn off electricity to the basement if it is safe to do so, and keep children and pets away.
If the water is clean, you can start drying the area with towels and a wet vacuum. Run a dehumidifier to pull moisture from the air. Open windows if the weather allows. For any water that looks dirty or smells like sewage, avoid contact and call the pros right away.
- Look for wet carpet, drywall, or baseboards
- Check the floor drain for backups
- Inspect any window wells for standing water
- Note any visible cracks in the foundation
- Smell for a musty versus sewage odor
Dry the Area Thoroughly
Drying is the most important step to stop mold growth. Remove wet rugs, furniture, and boxes from the area. Pull up wet carpet and padding if they are soaked, because padding holds water and dries slowly.
Use fans and a dehumidifier to speed up drying. Keep the air moving for several days. If you have wet drywall, cut out the damaged sections, since water wicks up and can hide inside the wall. The goal is to get everything dry before mold spreads.
When to Call the Pros
If the water came from sewage or if the flooding is deep, you need professional help. The pros have heavy-duty drying equipment and can find hidden moisture in walls and under flooring. They also handle contaminated water safely.
You should also call the pros if the smell persists after you dry things out. Lingering odor usually means moisture is still trapped somewhere. A water damage inspection can locate the source and check for mold growth behind walls or under floors.
- Water level is more than a few inches
- Water is dirty or smells like sewage
- Dampness spreads to multiple rooms
- You see visible mold growth
- The smell does not go away after drying
Prevent Future Smells
After the water is gone and the area is dry, look for ways to keep rain out. Fill small cracks in the foundation with hydraulic cement, and make sure gutters and downspouts direct water away from the house. If you have a floor drain, check that it is clear of debris.
Consider installing a backwater valve on your main drain line to prevent sewage backups during heavy rain. If you live in Mesa, keep your shutoff valve location written down. Also check that your basement floor drains have a trap with water in them to block sewer gases.
Is the Smell a Health Risk
Mold can trigger allergies, asthma, or other breathing issues, especially for people with sensitivities. If you feel unwell after being in the basement, see a doctor. Sewage contains bacteria and viruses, so avoid contact and get professional cleanup if you suspect a backup.
A musty smell alone does not mean you are in immediate danger, but it signals a problem that needs attention. The sooner you dry the area and fix the source, the lower the risk of mold spreading. For any large or contaminated water issue, call the pros to handle it safely.
Talk to someone now
Water keeps spreading into floors and walls, so it is worth acting early. Calls are answered 24/7.
Call Now (480) 898-4279Frequently asked questions
Why does my basement smell like sewage after rain?
A sewage smell after rain often means a sewer backup. Heavy rain can overwhelm municipal drains, causing sewage to back up through basement floor drains or toilets. It can also come from a dry drain trap that lets sewer gas escape. Avoid contact with dirty water and call a professional.
Can a musty smell go away on its own?
A musty smell usually does not go away on its own because it comes from mold and mildew that need moisture to grow. If you dry the area completely and remove wet materials, the smell may fade. But if moisture stays trapped, the odor will likely return or get worse.
Should I clean the basement myself?
For clean water from a minor leak, you can dry the area yourself with fans and a dehumidifier. But for sewage, deep flooding, or if you see mold, call the pros. They have the right equipment to dry hidden spaces and handle contaminated water safely.