Why does a scuba diver become dehydrated while diving?

well, i dont know but i think coz of the water deptand level!! but im not too sure so yeah!

Addition

Scuba cylinders are filled with very dry gas to prevent mositure from accumulating in them. Since the gas is very dry, your lungs will humidify the air you breath using your body's own moisture supply. Because you are humidifying the air from water within your own body, you lose moisture when you exhale and therefore you lose moisture due to breathing the dry air from the scuba cylinder and become dehydrated during a dive. On a side note, it is very important to stay hydrated since dehydration is a contributing factor to decompression sickness.