Back-flow preventers are used on buildings to prevent the mix of sewerage with other water systems. Back-flow preventers at the outfall points of municipal storm water systems are used by municipalities to prevent the rise of seawater up from the ocean or other waterways.
In the City of Miami Beach storm water flows to catch basins through large pipes into outfalls along the Biscayne Bay. When the sea level rises water flows more slowly or even flows from the water bodies to the streets. Currently Miami Beach is sub- ject to tidal flooding when water pressure rises. Back-flow preventers have been recommended as part of a system upgrade.