this is incorrect lol. the water is just to help with humidity, to prevent a dry mouth and sinuses. all resumed cpap machines for example can be used without the water tank as long as you have the backplate.

the water in the tank is heated to increase the humidity of the air circulating.

cpap machines work by increasing the air pressure on breath-ins and help open your airways by keeping your genioglossus tensor veli palatini muscles engaged.