Prevention of cross contamination of non-potable water to potable water systems and tidal backups from a larger drain system are an important concern that need to be addressed in any plumbing system.
A backwater valve is installed to protect your home or business from a massive backup of the larger sewer system, which your house sewer dumps into. A backwater valve is a mechanical device that can get stuck in the open position. This usually happens from an obstruction that does not belong in the line. The backwater valve has a door that swings one way and can freeze over time due to non-lubrication. Sewage backwater valves can only be installed when the drain it serves is lower than the lowest gravity-draining orifice respective to the gravity system it is tying into. We recommend strict adherence to what cannot go down the line when a backwater valve exists because they are prone to get clogged easily. It is also a good idea to have a visual inspection done once a year to ensure performance when needed.
Sump pumps and sewage ejectors have similar devices called check valves that work on a vertical pump discharge line. There are check valves used on domestic water systems to stop thermal cross over, and to maintain directional flow on a line with multiple pressure sources.
Another thing to consider when addressing backflow prevention is to make sure you have vacuum breakers on all handheld devices and hose faucets.