What happens to the pressure of water as depth under the water increases?

The pressure of water increases as the depth under the water increases.

Water pressure rises with depth because the water above a given point has weight. That overlying water exerts force on the layers below, so a diver or underwater instrument experiences progressively greater pressure the farther down it goes. In a calm, uniform body of water, the increase is described by hydrostatic pressure: pressure depends on the fluid’s density, gravitational acceleration and depth.

At the surface, water pressure is often discussed in addition to atmospheric pressure. Moving downward adds the pressure produced by the water column. This is why swimmers may feel pressure in their ears and why deep-sea vehicles must withstand enormous forces on their hulls. Salt water produces slightly more pressure per metre than fresh water because it is denser.

A common misconception is that pressure increases because water is “compressed” by depth in the same way air is. Water is only slightly compressible; the main reason for the increase is the weight of the water column above the point being measured.