We need a way to detect water underground

As a player, I need a way to easily detect water underground so that I can more easily customize my world without spending significant time searching randomly for underground pools or aquifers.

There are a number of ways this could be done. For example, a new block could be added to the game that give additional utility to already existing items, such as the prismarine crystal. Another avenue is either adding functionality to current mobs in the game or creating a new mob that can exhibit behaviors that would indicate there is a water source block nearby. Behaviors that come to mind are digging, burrowing, or making a sound. 

How this could look in practice would be the block or mob is within 16 blocks of a water source and changes its state or behavior. If this is a block, the block may make a sound, emit a light, or change color/shape. This block state change would be detectable by redstone.