Quick Answer:
If you turn the water back on after winterization and see water moving between bowls or fixtures, stop using those fixtures and check traps and valves right away. This swapping of water usually means vents, traps, or valves didn’t return to normal after draining for winter. Do a quick inspection, refill traps, and test drainage to confirm whether the problem clears or needs a plumber.
Why This Happens
During winterization plumbing is drained to prevent frozen pipes. If traps, vents, or fixture shutoffs aren’t restored correctly, air pressure shifts or open paths in the drain allow water to move from one bowl or fixture into another. Partial thawing, shared drain lines, or faulty shutoff valves can make the movement obvious when you turn water back on. If the problem is not constant, **Cross-flow occurs intermittently**; if it is moving from one toilet to another, you may see **Water flows into opposite bowl**.
Step-by-Step What to Do
1. Stop using affected fixtures
- Turn off faucets and avoid flushing toilets until you inspect.
- Shut the house water main if multiple fixtures show problems or if you smell sewage.
2. Open a faucet to relieve pressure
- Open a cold-water faucet at the highest point in the house and one at the lowest to allow air to escape as you restore water.
3. Inspect visible traps and valves
- Look under sinks and behind appliances for disconnected or damaged P-traps and for closed shutoff valves that need opening slowly.
- Check toilet tank fill and make sure the bowl is filling normally after the tank refills.
4. Refill traps fully and test drainage after winterization
- Pour water into each fixture drain (sink, shower, floor drain) so the trap has a full water seal. For toilets, flush and allow the bowl to refill.
- Run each fixture briefly to confirm water drains away and the trap holds water without cross-flow.
- If a trap empties again quickly or water backs into another fixture, do not use those fixtures until fixed.
5. Check vents and shared drains
- Look for blocked roof vents or signs of shared drain issues (multiple fixtures affected). Partial venting problems can create suction that siphons traps.
6. Isolate the issue
- Close individual shutoffs and test fixtures one at a time to find which line or fixture is the source.
What Not to Do
- Do not leave traps dry after winterization.
- Do not pour strong drain chemicals to force clogs through; those can damage pipes and create hazards.
- Do not try to force water through a suspected broken or frozen pipe without locating the shutoff first.
When to Call a Professional
- Call a plumber if you see sewage backing up, persistent cross-flow after refilling traps, foul odors that don’t clear, or any signs of cracked or leaking pipes.
- If you cannot restore proper trap seals or if multiple fixtures share the problem after you’ve tested them individually, get professional help.
Safety Notes
- Turn off the water main before working on plumbing and know where it is located.
- Avoid mixing cleaning chemicals and wear gloves and eye protection when handling unknown residues left from winterization.
- If you suspect a burst or leaking pipe, shut off water and electricity in the affected area if it’s safe to do so, then call a pro.
Common Homeowner Questions
- Why does this start only after winterization? Draining and refilling changes trap seals and pressures; if traps aren’t refilled or vents are blocked, cross-flow can occur.
- Will refilling traps usually fix it? Often yes—refilling and testing drainage fixes many cases, but persistent issues need a plumber.
- Is this a health risk? It can be if sewage backs up or odors persist—stop using affected fixtures and call a professional.