Water Path Magic to give Water Breathing is posted in the FAQ at the top. It's WaterPath*2 Total Size. Water 1 = Up to Size 2 of Units, Water 2 = Up to Size 4, etc. So in order to take an Elephant underwater you'd have to have at least Water 3.

Certain Creatures and Magic Items have different formulas, I thought I had changed the MIQR in order to give a total size, but that must have been the one I had a work instead of the one at home since it still has the old values.