Check the depth for which the camera is water sealed. Many will fail at a pressure larger than 1 atmosphere, about 10 meters depth at sea level. This is to allow for falling into the water. At greater depths water may work its way into the camera.
The Nikon AW110: Capacity to shoot pictures underwater up to a depth of 18 m (59 ft) and for 60 minutes
Repetitive dives may break the seals.
The underwater housings for dSLR/SLR are designed for greater depths and require regular cleaning, lubricating, and repairing to keep the seals properly. Also most divers check the housing for leaks before leaving the surface and while descending to see if any air leaks out. The extra space allows for control arms, buoyancy, and a small safety margin when a leak develops.