Finite Water Control is successor in function to Regional Water. Water (and other fluids, if specified in the config) does not form into new source blocks when outside of specified dimensions, biomes, or y-levels.
FWC is intended to allow pack-makers and players to make obtaining large amounts of water more challenging than it is in vanilla Minecraft. Players can pipe water in from oceans or rivers, but can't set up infinite water sources of their own.