It allows the Spelunker to swim inside the block and jump off the surface. Spelunkers can jump directly off the top of water with a well timed jump to avoid Piranhas. It is impossible to take damage from water, as you cannot drown and it will deny fall damage.
After falling deep enough into water, you cannot damage monsters by jumping on them. Caution is advised whilst fighting in water. It is possible to stomp monsters in water if they're close to the surface.
Piranhas can be found in water; in fact, they cannot survive outside of it. Other enemies can fall and act normally in water; however, if a Fire Frog falls into water, it is defused, becoming a normal frog. It is possible for this to happen while you are holding it, resulting in it attacking you once you release it.
If a Flooded Cavern Level Feeling occurs, the bottom of the level will be flooded with water. Many Piranhas are found in the flood water, along with Old Bitey. However, living piranhas will not appear in a Restless Dead Level Feeling; in that case, their skeletons will be found instead. Bodies of water can also be found in The Ice Caves , providing them an area to spawn.