I have a cat who started life as a feral kitten. He was found at the side of the road, near death, aged about 12 weeks and is now a fat 6 year old neutered tom. He had to have a back leg and part of his tail amputated, he has a cataract in one eye and the other has a mis-shapen pupil, but this doesn't seem to affect his vision. He's an indoor cat because he's too stupid to find his way home; there may be some brain damage from his near-death incident.
So, background given! His water bowl is a large square tupperware-type plastic bowl, it may have been designed as a cake tin. When it is freshly filled with water he tends to drink from the furthest corner from where he's standing, and to do this he stands with one or both front paws in the water. Sometimes he paws at the surface of the water before drinking. He doesn't do this when the water is less fresh and/or the water level is lower.
So, why does he do this, do you think? His balance, his sight, his stupidity? No other cat I have had has done this.