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Why Does My Water Smell Bad After Flooding?

Last updated October 31, 2026

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The short answer

Common Causes of the Smell

Floodwater often contains a mix of groundwater, sewage, agricultural runoff, and decomposing material. When this water enters your plumbing system through cracks, broken seals, or backflow, it can leave behind bacteria and organic matter that cause a strong smell. Even after the visible water recedes, residue can linger in pipes, fixtures, and water heaters.

Another cause is stagnant water sitting in your pipes or water heater for days. Bacteria like sulfur-reducing microbes thrive in warm, still water and produce hydrogen sulfide gas, which smells like rotten eggs. Mold and mildew can also grow in damp areas and give your water a musty or earthy odor. The exact cause depends on the flood source and how long water sat.

Is It Safe to Use That Water?

If your water smells bad, treat it as unsafe until you know otherwise. Floodwater can introduce contaminants like sewage, fuel, or chemicals. Do not drink, cook with, or bathe in water that smells unusual. Boiling removes some bacteria but not chemicals or heavy metals, so it is not a reliable fix. See a doctor if you feel unwell after any contact.

Your local water utility can tell you if the public supply is affected. If you use a private well, floodwater can contaminate the groundwater, and you should have the water tested before using it again. In the meantime, use bottled water for drinking and cooking. Keep children and pets away from tap water until you know it is safe.

  • Avoid drinking or cooking with smelly water
  • Do not use it for brushing teeth or making ice
  • Keep pets from drinking it
  • Boiling does not remove chemicals or heavy metals
  • Check with your water utility or test a private well
  • Flush pipes only after the source is confirmed safe

What You Can Do Right Now

Start by turning off the water supply to your home if you can locate the shutoff valve. This stops more contaminated water from entering your plumbing. If you live in Fresno, keep your shutoff valve location written down so you can act quickly during an emergency. Do not run water through the system until you have assessed the situation.

You can also open a faucet for a few minutes to see if the smell clears, but only if you are certain the supply is not contaminated. If the smell persists, the issue is likely inside your plumbing or water heater. Do not attempt to dismantle pipes or appliances yourself, as that can cause more damage. Note the smell and any discoloration to share with a professional.

When to Call the Pros

A water damage pro can inspect your plumbing, water heater, and well system to find the source of the odor. They have tools to test for bacteria, chemicals, and other contaminants. They can also identify hidden water damage in walls or floors that may be contributing to the smell. The work usually involves flushing, cleaning, and sometimes replacing affected parts.

The pros can also help with broader cleanup if your home was flooded. They can remove contaminated materials, dry out the structure, and treat surfaces to prevent mold growth. The cost depends on the extent of the damage, the type of contamination, and the work needed. Contact a local water damage pro for an assessment of your situation.

  • Inspect plumbing and water heater for contamination
  • Test water for bacteria and chemicals
  • Flush and disinfect pipes and fixtures
  • Identify hidden moisture in walls and floors
  • Remove and dispose of contaminated materials
  • Dry and treat areas to prevent mold

Preventing Future Odor Problems

After a flood, have your water system inspected and cleaned before regular use. This includes flushing all faucets, cleaning aerators, and draining and disinfecting the water heater if it was affected. A water damage pro can guide you through the process or do it for you. Keeping your plumbing well-maintained reduces the risk of bacteria growth.

  • Flush all faucets after a flood
  • Clean or replace aerators and screens
  • Drain and disinfect your water heater
  • Test well water for bacteria and chemicals
  • Install a backflow preventer
  • Seal cracks in pipes and foundations

Water damage does not wait

Phones are answered 24/7 for Fresno and nearby communities.

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Frequently asked questions

Why does my water smell like rotten eggs after flooding?

Rotten egg smell is usually from hydrogen sulfide gas produced by bacteria in stagnant water. Floodwater can introduce these bacteria into your pipes or water heater. The smell is a sign of contamination, so avoid using the water until you know it is safe.

Can I boil the water to make it safe?

Boiling kills bacteria, but it does not remove chemicals, heavy metals, or some contaminants found in floodwater. It can also concentrate certain substances. Do not rely on boiling as a fix. Use bottled water until you have tested the water or confirmed it is safe from your utility.

How long will the smell last?

It depends on the source. If the contamination is in your pipes, flushing and disinfecting may clear it within a day. If it is in your water heater or well, it may take longer. A water damage pro can assess the situation and recommend the right steps.

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