Quick Answer:
If you see water moving from one basin or toilet bowl to another after the city restores service, it’s usually from sediment or pressure changes in a shared branch. First, stop using the affected fixtures and flush cold water through the line to clear shifted sediment. Run the cold faucet until water runs clear and steady. If it doesn’t clear after several minutes, contact a plumber.
Why This Happens
When municipal supply is shut off and then turned back on, flow reversals and pressure surges can dislodge mineral deposits, sand, or rust inside pipes. Those particles travel with the water and can collect at low points or in branch lines feeding a sink or toilet. That can create unusual flows—for example, water moving from one bowl to another—or temporary clogging and discolored water.
This is similar to problems people see after winter work on pipes; see Cross-flow after winterization for related issues and prevention tips.
Step-by-Step What to Do
1. Stop using affected fixtures
- Avoid flushing toilets, running washing machines, or using the dishwasher until the water clears. That prevents more sediment from being pushed into the branch line or appliances.
2. Check the main supply and neighbors
- Confirm the city water is fully restored and that neighbors aren’t reporting the same issue. If the problem is localized to your home, proceed to the next steps.
3. Flush the cold line to clear sediment
- Open the lowest cold-water faucet in the house (often a basement utility sink) to let air and particles exit the system.
- Then, open the affected cold faucet or fixture and run it at full cold until the water runs clear—this may take 5–15 minutes depending on how much material moved.
- Do not run hot water yet; flushing cold first reduces the chance of dragging sediment into the water heater.
4. Clean aerators and strainers
- Remove faucet aerators and showerhead screens and rinse out any trapped grit. Reinstall them after the water runs clear.
5. Test fixtures and appliances
- Run water at other fixtures briefly to confirm the issue was isolated and that water is clear systemwide.
- If one fixture still shows backflow or bowl-to-bowl movement, try the basic trap and vent checks or proceed to the next step.
6. If flushing doesn’t fix it, shut off and call
- If sediment keeps returning, or you notice persistent cross-flow between bowls or strong odors, shut off water to the affected branch (if possible) and call a professional.
If the symptom looks like one basin filling while another drains, that can indicate a trap or venting problem; see advice on One sink fills when other drains for diagnostics that overlap with this situation.
What Not to Do
- Do not drink discolored water immediately after outages.
- Do not run hot water first to flush the system—this can carry sediment into your water heater and spread the problem.
- Do not use chemical drain cleaners to try to clear sediment in supply lines; they won’t help and can be hazardous if used improperly.
When to Call a Professional
- If flushing cold lines for 10–15 minutes does not clear the water.
- If you have continuous discoloration, strong metallic or sewage odors, or repeated cross-flow between fixtures.
- If multiple fixtures are affected or water pressure is poor after flushing, which may indicate a larger issue in a branch or the meter/service line.
Safety Notes
- Avoid drinking, cooking, or brushing teeth with discolored water. Use bottled water until water runs clear.
- When flushing, be careful around slippery floors and tubs—sediment can make surfaces slick.
- Turn off power to appliances if you suspect sediment might have entered them, and follow manufacturer guidance before running them again.
Common Homeowner Questions
- Why is the water brown after the city turned it back on? Brown water is usually rust or sediment dislodged in the mains or your pipes. Flushing cold lines typically clears it.
- How long should I flush the line? Run cold water until it clears, often 5–15 minutes; longer if the line is long or heavily contaminated.
- Will this damage my water heater? If you run hot water before clearing cold lines, sediment can enter the heater and cause issues. That’s why you should flush cold first.