The elevation of a structure above the nearest water level is the position of its base (as defined in "base of a structure") above the closest body of water, such as a river, stream, ocean, or lake. This data may be used to determine the susceptibility of a structure to flooding.

The lower reference is the local water surface. Base elevation uses mean sea level, which can differ substantially from the level of a nearby inland lake or river.

A change in the nearby water level changes this separation without changing the structure's base. The value alone therefore does not establish whether all possible flood levels remain below the building.