I was told by a friend they found a small snake around their water tank. It was hiding under the 5000 gallon rain tank by sliding into the corrugated iron wave it rests on.
Some are placed on sand or gravel and different types of snakes are known to call that home for a while. The lady who told me of this had an Australian brown snake there.
Our neighbor knew of this habit and has placed small stones at the base, ours had nothing at all and could have been a perfect hiding place.
I think if there is a slow leak that may encourage frogs or other small prey. What do snakes eat? Yes, you go it right - frogs and small prey. Keep the area around the base clear and that should act as a good deterrent.