Quick Answer:
If you notice an egg-like smell after a repair, it’s most often hydrogen sulfide from stagnant water, disturbed sediment, or a dry trap — not a new toxic contaminant introduced by cutting the pipe. Start by isolating the repaired branch and flush the repaired branch line into a bucket to see if the smell comes from that section. Follow the step-by-step checks below; if the smell persists or is strong, call a professional.
Why This Happens
- Stagnant water in a newly opened branch can release hydrogen sulfide as trapped organic matter or bacteria are disturbed.
- Hot-water systems sometimes produce a sulfur smell if bacteria grow on the sacrificial anode or in the tank; this often affects hot water only.
- A dry P-trap (drain trap) left open during repair can let sewer gas into the house, smelling like rotten eggs.
- Well water naturally higher in sulfur compounds will smell when flow is low or when lines are disturbed.
If the smell returns periodically, read more about Smell returns every few weeks. If it’s mainly when you run the shower, see Sulfur odor when running shower.
Step-by-Step What to Do
1. Isolate the repaired branch
Close the local shutoff valve for the repaired line if you can. This helps you test that branch without affecting the whole house.
2. Flush the repaired branch into a bucket
Open the nearest fixture on that branch and collect water in a bucket until it runs clear and any strong odor decreases. Dispose of the water outdoors or down a drain with good ventilation. Note whether the smell is strongest at first and fades with flushing — that points to stagnant water or sediment in that branch.
3. Compare hot and cold water
Run cold water first, then hot. If only the hot water smells, the water heater is likely involved. If both smell, the issue is upstream or in the repaired branch.
4. Check drains and traps
Make sure sinks and floor drains on the repaired branch have water in their P-traps. Pour a small amount of water into each trap to reseal them if they were drained during the repair.
5. Clean fixtures and aerators
Remove and rinse faucet aerators and showerheads. Sediment or biofilm can collect there and cause odors when water flows through.
6. Run fixtures and monitor
After flushing and cleaning, run the fixtures for a few minutes to ensure fresh water replaces standing water. Keep a note for the next few days to see whether the smell comes back or disappears entirely.
What Not to Do
- Do not pressure-test freshly repaired lines for odor.
- Do not mix household cleaners (for example, bleach and ammonia) to try to eliminate smells.
- Do not ignore a persistent, strong odor or any symptoms like headaches, nausea, or dizziness.
When to Call a Professional
- If the smell does not fade after thorough flushing and cleaning.
- If the smell is concentrated, causes health symptoms, or you suspect a sewer gas leak.
- If you have a private well and suspect hydrogen sulfide or other contaminants — a licensed well contractor or water treatment pro can test and treat the source.
Safety Notes
- Low levels of hydrogen sulfide smell like rotten eggs and are usually not dangerous, but higher concentrations can be harmful. If you experience breathing difficulty, dizziness, or nausea, get fresh air and seek medical help.
- Ventilate the area while flushing and avoid prolonged exposure to strong odors.
- For water-system disinfection beyond basic flushing (for example, shock chlorination of a well), consider hiring a professional to avoid improper chemical use.
Common Homeowner Questions
- Why did it start right after the repair?
Disturbing pipes can release trapped sediment or air and expose stagnant water, which often smells until flushed out. - Is the water safe to drink?
If the smell disappears after flushing, it’s usually not a safety issue. If it persists or you have a well, get the water tested before drinking. - Will the smell go away on its own?
Often it will after thorough flushing and cleaning. If it returns or is only from hot water, further investigation is needed.
For more related articles, see the Sulfur / Rotten Egg Smell in Water hub.