A sewer line carries wastewater from toilets, sinks, showers, and appliances inside your home to a treatment system, while a storm drain carries rainwater and runoff from streets, roofs, and yards. In most areas, the two are meant to stay separate.
What the Sewer Line Does
Every drain inside the house connects to the main sewer line, which runs underground to the public sewer in the street. That wastewater is treated before it is released. Sewer lines are sized for the normal flow from homes, not for large amounts of rain.
What Storm Drains Do
Storm drains are the grates you see along curbs and in parking lots. They collect rainwater and send it through separate pipes, often to nearby waterways. Because storm water is usually not treated, nothing besides rain should go into them.
Why Keeping Them Separate Matters
- Rainwater in sewer lines can overload them and cause backups into homes
- Sewage or chemicals in storm drains can pollute local waters
- Many towns do not allow downspouts or sump pumps to connect to the sewer line
- Grease, paint, and motor oil should never be poured into either one
Signs Something Is Connected Wrong
If your basement drains back up during heavy rain, it may be because storm water is entering the sewer somewhere, either in your home or in the public system. A downspout or sump pump tied into the sewer is one possible reason. A camera inspection and a look at your drainage can help find the cause.
Local rules decide what is allowed, so check before changing any connections.
If rain seems to trigger backups in your home, a look at the sewer line and its connections can help sort it out. For questions about downspouts and drainage around the house, you can talk to a plumber about your setup by calling (833) 603-1840.