Water pressure is the amount of force per unit area that water exerts,
say, on the container it's in or on a submerged object.
The pressure of water that's not moving depends on the depth. It's given by the formula
P = density * g * depth
where the density of water is 1000 Kg per cubic meter, and g is the
gravitational constant at the Earth's surface, 9.81 meters/second**2.
The depth is in meters. Then the pressure will be in Pascals, the
metric unit of pressure.
If you want the total pressure, you also have to add on one
atmosphere's worth of air pressure, about 100,000 Pascals. It takes
about 10 meters of depth for the water pressure to be about an
atmosphere, for a total pressure of two atmospheres.
(republished on 08/02/06)