What is the ambient pressure at 50 meters under water

Answer: about 5 bar or 72 pounds per square inch - depending on the salinity of the water as sea water has slightly greater density.

"At sea level, the air that surrounds us presses down on our bodies at 14.5 pounds per square inch (1 bar). You don't feel it because the fluids in your body are pushing outward with the same force."

"The deeper you go under the sea, the greater the pressure of the water pushing down on you. For every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi (1 bar). In the deepest ocean, the pressure is equivalent to the weight of an elephant balanced on a postage stamp, or the equivalent of one person trying to support 50 jumbo jets!"

http://oceanservice.noaa.gov/facts/pressure.html