During periods of heavy rainfall, municipal sewer lines can become overloaded, resulting in backups into homes situated in low-lying areas. A backwater valve can prevent sewage from backing up into your home and causing potentially substantial damage.
The backwater valve is installed on the main line carrying waste water from your home to the municipal sewer. It may be placed either in your basement, under the floor, or outside your house where the main line leaves the building.
Under normal conditions, the valve stays open, allowing waste water to travel freely from your home to the municipal sewer line. But if the municipal line backs up, the valve closes, preventing the backup from entering your home.
In some municipalities, backwater valves are mandatory in new homes. Older homes can be retrofitted, although this is more costly. In some areas, the cost of installing a backwater valve in an existing home may be partially subsidized or qualify for a rebate. Check with your municipality to find out about programs in your area.