Definition - What does Backwater mean?
Backwater, or backflow, is the unintended inflow of water and sewage into sewer mains and laterals which serve homes, businesses and stormwater drainage systems. The system overload usually results from excessive precipitation. Prevention involves a backwater valve, which is similar to a check valve since it only allows water to flow in one direction. The difference between backwater preventer and the check valve is that the backwater preventer uses a rubber flap to prevent the undesirable inflow, whereas a check valve uses a spring-loaded mechanism to ensure water can only pass through it in one direction.
Trenchlesspedia explains Backwater
A backwater valve isn't the same as a backflow preventer. The backwater valves mission is to prevent raw sewage from backing up into your home or business through the laterals that connected to the sewer main, much like a computer's firewall is the first line of defense against malware infection on a computer. The backflow preventer, on the other hand, works within your home or business. Attached to a potable water source (city water lines or water wellhead), it prevents a reverse flow of greywater into a potable water system.