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.

Kind of, yeah. When I first got onto CPAP I was worried that it would cause my muscles to atrophy over time because it makes the inhale so much easier. But the pressure is still there on the exhale, which is exactly like breathing out through a straw into water (with 5-20cm water on top of the straw, depending on the CPAP pressure).