Quick Answer:
If your water smells like rotten eggs after a city outage, it’s usually hydrogen sulfide from sediment or bacteria stirred up when the utility flushes pipes. First, call the utility to confirm line flushing and retest after 24 hours. In most cases the odor clears after the system settles and a short flush of your own pipes.
Why This Happens
When the city restores service after an outage they often flush mains to clear debris. That can disturb mineral or organic matter in older pipes or at dead-end lines. Water heaters and plumbing fixtures can trap that material, so hot water can smell more than cold. Small amounts of hydrogen sulfide gas cause the familiar sulfur or “rotten egg” odor; it’s usually an annoyance rather than an immediate health hazard at low levels.
Step-by-Step What to Do
1. Confirm the utility action
Call your water utility to find out if they flushed lines near your neighborhood. Ask when they did it, where, and whether they recommend waiting before retesting. This step helps rule out other causes and gives you a timeline for when to check again.
2. Retest after 24 hours
Follow the utility’s guidance and plan to check water again about 24 hours after their flushing. Many odors fade once the system has had time to re-stabilize. If the smell is gone at that point, the problem was likely temporary — see Smell disappears after flushing system for related guidance.
3. Flush your own pipes safely
- Run cold taps for several minutes starting at the tap nearest the street, then move to others. Run outside hose bibs too if you have them.
- Check hot water separately — if only hot water smells, the water heater may need a simple flush or inspection.
- If flushing fixtures clears the smell, test water again the next day to confirm it stays clear.
4. Test water if odor persists
If the smell continues after 24–48 hours, consider a basic water test through your utility or a certified lab to check for hydrogen sulfide and other common contaminants. That will tell you whether the odor is from bacteria, minerals, or something else.
What Not to Do
- Do not install carbon filters until flushing is complete. Installing a filter while sediment or bacteria are present can trap organics and make odors worse.
- Don’t panic and replace plumbing pieces immediately—most cases clear after flushing and retesting.
- Avoid using aggressive chemical treatments on your own unless a professional recommends them based on test results; improper use can damage plumbing or create other hazards.
- If you’ve recently installed a new filter and noticed a new odor, check resources about Egg smell after installing filter before making further changes.
When to Call a Professional
- If the odor persists more than 48–72 hours after the utility confirms flushing and you’ve retested.
- If the smell is very strong, appears in only one tap, or is accompanied by discolored water — this can point to localized plumbing problems.
- If testing shows bacteria, a licensed plumber or water treatment specialist can recommend safe disinfection steps for your water heater and private plumbing.
Safety Notes
- Low levels of hydrogen sulfide smell are usually not dangerous, but strong concentrations can be harmful. If you experience headaches, dizziness, or nausea, leave the area and seek fresh air.
- Boiling water can concentrate odors; do not assume boiling will remove hydrogen sulfide.
- Don’t mix household chemicals to try to treat water; that can create toxic gases.
Common Homeowner Questions
- Why does only my hot water smell? Often the water heater traps bacteria or sediment; flushing or disinfecting the heater can help.
- Is it safe to drink? Short-term exposure to a sulfur smell is usually an odor issue rather than a health emergency, but if the smell is strong or testing shows contaminants, avoid drinking until cleared.
- How long should it take to go away? In most city flushing cases the smell resolves within 24–72 hours after the utility action and a brief home flush.
For more related articles, see the Sulfur / Rotten Egg Smell in Water hub.