Quick Answer:
If an odor appears only after pipes were opened during a repair, the smell usually comes from debris, trapped air, disturbed biofilm, flux or solvents, or a water heater reaction. Start by running cold and hot lines separately to find which line carries the smell, flush the affected fixture and traps, and check the water heater and vents. If it persists or smells like sewer gas, call a professional.
Why This Happens
When a plumber opens pipes for repair, anything inside the pipe or nearby can be disturbed. Common causes right after repair include:
- Leftover solder, flux, pipe dope, or cleaning solvents that release an odor when wetted.
- Dislodged biofilm or sediment that releases smell as it moves through the lines.
- Dry or damaged P-traps that allow sewer gas into the room after work around drains.
- Water heater issues (anode reactions or disturbed sediment) that create a rotten-egg or metallic smell in hot water.
- Air pockets that concentrate odors until the line is fully flushed.
If the odor shows up only after a repair, it’s often local (a single fixture or branch) rather than the whole house supply.
Step-by-Step What to Do
Step 1 — Stop and note where and when the smell appears
Check which fixtures and which water temperature produce the odor. Is it only at one sink, only in hot water, or in multiple spots? This observation directs your next steps.
Step 2 — Run cold then hot lines separately to isolate odor source
Open the cold faucet fully and let it run for 1–3 minutes, then smell the water at the stream and at the drain. Close it and repeat with the hot faucet. Running the cold line first helps identify upstream contamination; running hot separately points toward the water heater or hot-only contaminants.
Step 3 — Flush the affected fixture and aerator
Remove and rinse faucet aerators and strainers. Run the line at full flow for several minutes to clear debris and trapped air. For a toilet or floor drain, pour a bucket of water to ensure the trap is sealed and flush out standing water.
Step 4 — Check and refill P-traps and clean drain paths
Make sure all nearby traps have water in them (pour a cup of water into rarely used drains). If a trap was removed for repair, reinstall it correctly. Clean visible debris from drains and wipe surfaces—sometimes odor comes from the repair site, not the water itself.
Step 5 — Inspect the water heater if the smell is only in hot water
If hot water smells while cold does not, suspect the water heater. Sediment or a sulfate-reducing bacteria reacting with the anode can make a rotten-egg smell. Flushing the tank can help, but follow manufacturer guidance and turn off power or gas before doing any work. If you see corrosion or persistent odors after flushing, get a pro to inspect the heater.
Step 6 — Test other fixtures and outside faucets
Run water at other fixtures to confirm whether the problem is isolated. If the odor is present only in the repaired area, the cause is likely local to that work. If it’s widespread, it might be a supply issue or something at the heater or mains.
Step 7 — Note any other symptoms
Look for discoloration, sediment in the stream, or irregular pressure. If you notice unusual leaks, random noises, or dripping after the repair, consult the relevant advice on Random dripping after repair to confirm the repair quality and next steps.
What Not to Do
- Don’t mask odors with chemicals. Covering the smell can hide a real problem and create unsafe conditions.
- Don’t drink the water until you’re certain the smell comes from a non-toxic source, especially if it smells chemical or sewage-like.
- Don’t open or attempt to service the water heater without shutting off power or gas and following manufacturer safety steps.
When to Call a Professional
- If the smell persists after flushing lines and cleaning aerators.
- If the odor resembles sewer gas (strong rotten-egg smell), or if you suspect a broken vent or trap—this can allow sewer gas into the home and needs a plumber.
- If the smell is only in hot water and does not improve after flushing the heater, or if you see corrosion—call a licensed plumber or water heater specialist. A pressure or supply issue after heater work may point to a larger system problem; consider checking advice about Pressure imbalance after water heater install when discussing symptoms with the pro.
Safety Notes
- Ventilate the area while you investigate odors. Open windows and run fans if it’s safe to do so.
- If you need to work on a water heater, always turn off electrical power at the breaker or shut off the gas and follow manufacturer instructions.
- Wear gloves and eye protection when cleaning aerators, drains, or handling standing water and debris.
- If you suspect contamination beyond an odor (discolored water, illness symptoms), avoid using the water for drinking or cooking until tested or cleared by a professional.
Common Homeowner Questions
- Why did the smell start only after the plumber opened my pipes?
Opening pipes can dislodge sediment, biofilm, or leave temporary residues (flux, cleaners), which release odors when wetted. - How long should flushing take before the smell is gone?
Often a few minutes of full-flow flushing clears the smell; if it persists after 10–15 minutes, investigate other causes. - Is it safe to drink the water while it smells?
If the odor is mild and smells like solder or flux after a repair it may be temporary, but avoid drinking if it smells like sewage, chemicals, or if you’re unsure—call a plumber or water authority for testing.