What's the relation between the head of water column in atank and its pressure?

Assuming the water in the tank is not flowing, and there is no other pressure source in the tank, then the pressure at the bottom of the tank is directly related to the head, as follows:

P = (unit weight of water)* h

At room temp the unit weight of water is 62.3 lb/ft^3

See: Head (hydraulic - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Head_(hydraulic)) for a more detailed explanation.

whats the relation between the head of water column in atank and its presure? what the height of the tank(bottom of tank); let say it is 30 ft H, 30 X0.433 =13 psi (G),1cubic ft of water =62.4lb, 62.4/ 144=0.433