Why are water storage tanks usually built on towers or hilltops?

They need distance from the earth surface to enable acceleration due to gravity provide pressure that will enable flow of water to people downhills. Bcz they need particular distance from earth's surface. That's why they can able to transfer water to dams, people through any medium.

They are built on hilltops and tower because they need distance from the earth surface to enable acceleration due to gravity provide pressure that will enable flow of water to people downhills