5.2: Hotfix for a concurrent modification error
5.3: Removed diagonal water flow (still renders diagonally)
5.4: Fixed inaccurate warnings on mod fluids
NB: There is a config option for height of rain; I suggest leaving it at 0 or 1 unless you don't mind water floating in the air.
NB: Bodies of water will overfill in rain; I have not been able to track down why. You may consider the slight beach flooding to be a good thing.