Quick Answer:
If your sink begins to rise when it rains hard, stormwater is likely overwhelming the drainage system or pushing back through a shared drain line. Stop using affected fixtures while the rain is ongoing, note when and how it happens, and check other drains and the sewer cleanout. If the problem repeats or sewage is involved, get a plumber or your water department involved.
Why This Happens
Heavy rain can overwhelm municipal sewers, overload combined sewer/storm systems, or raise groundwater and stormwater levels around your home. When the downstream system is full, water looks for the easiest escape path — which can be your sink, floor drain, or other low points in the plumbing. Blockages in the lateral sewer line or missing backflow protection make it easier for that return flow to reach fixtures. Internal backups may also be intermittent depending on where the system is constrained; for related intermittent issues, see Sink backs up intermittently.
Step-by-Step What to Do
Observe behavior during heavy rain
- Watch the sink and other nearby drains while the rain is falling. Note whether water rises immediately when rainfall starts, only after heavy downpours, or after the storm ends.
- Record times, duration, and how much the water rises. Take photos or short videos if you can safely do so — this helps a plumber or utility diagnose the problem.
Stop using plumbing while the backup is active
- Avoid running taps, flushing toilets, or using appliances that send water to the same drain. Extra water makes backups worse.
- If the water appears to be sewage, avoid contact and keep household members and pets away from the area.
Check other drains and the cleanout
- See whether toilets, floor drains, or other sinks are affected at the same time. If multiple fixtures show problems, the issue is likely in the main lateral or municipal line.
- Locate the sewer cleanout (often a capped pipe near the foundation or property line). If water is backing out of the cleanout, that confirms an overload or blockage downstream.
- If the sink only rises when a floor drain or utility drain runs, compare behavior to **Sink fills when floor drain used** for insight.
After the rain: clear small clogs and monitor
- Once the system is no longer under stress, try running a small amount of water through fixtures to see if normal flow returns.
- Do not use chemical drain cleaners if sewage may be present; they can be dangerous and often won’t clear a mainline issue. Mechanical snaking by a pro is safer and more effective for mainline blockages.
- If gutters, downspouts, or grading are contributing to pooling near the foundation, address those drainage issues to reduce external pressure on your sewer system.
Document and prepare for a service call
- Gather your notes, photos, and times of incidents. This makes diagnosis faster and less expensive.
- If the cleanout shows backup or multiple fixtures are affected, contact a licensed plumber or your municipal water/sewer department.
What Not to Do
- Do not assume storms won’t affect plumbing — even short, heavy rains can force water back into drains.
- Do not stand in or touch standing water that may contain sewage; it is a health hazard.
- Do not pour chemical drain cleaners into drains that are backing up with sewage or stormwater; these products can cause burns and damage pipes, and they rarely fix mainline problems.
- Do not attempt major trenching or rerouting of sewer lines yourself; those jobs require permits and professionals.
When to Call a Professional
- Call a licensed plumber if backups recur, multiple fixtures are affected, or you have sewage in the home.
- Contact your municipal sewer authority if the cleanout shows stormwater coming back up or if neighbors are experiencing similar issues — it may be a public system overload.
- Request a camera inspection if the source isn’t obvious; this locates breaks or blockages in the lateral that you can’t safely inspect yourself.
- Consider a plumber for installing a backwater valve if the problem is confirmed to be sewer backup from the street side. Installation should be done by a pro and may require permits.
Safety Notes
- Avoid contact with water that may contain sewage. Wear gloves and waterproof boots if you must inspect affected areas after the fact.
- Do not use electrical appliances near standing water; shut off power to affected areas if there is any risk of electrocution and you can do so safely.
- Stay off ladders or roofs during heavy rain. Exterior checks like clearing gutters are safer after the storm has passed.
- When in doubt about hazardous conditions, wait for a professional rather than risking injury or exposure.
Common Homeowner Questions
- Why does this only happen in heavy rain? Municipal and combined systems can become overloaded during heavy downpours; when they’re full, water flows back into the lowest connected openings of your plumbing.
- Can I prevent it myself? Fixing grading, gutters, and downspouts around the house helps, but preventing sewer backup often requires a plumber-installed backwater valve or municipal action.
- Is this an emergency? If sewage enters the home, yes—call a plumber immediately. If water merely rises somewhat but drains away and there’s no sewage, document and monitor until a professional can inspect.