Does the shape of an elevated water tank has a significance to its function?

Question

Aside from draining purposes, why is it that most of the elevated cylindrical water tanks have a bottom with an inverted dome shape?

Answer 1

"Aside from draining purposes" I think that is large part of the reason, another reason might be that a dome can be self supporting even if made of thin plate, the stresses would be mostly tension, (supposing the cylindrical portion is supported by other structures)  while a flat bottom would need additional support.