Who drinks most water?

Take a regular cylindrical glass full of water. Four friends, Adam, Beatrice, Carl and David drink its content the regular way (by tilting the glass in their mouth).

• First, Adam drinks until the water surface is connecting points $A$ and $B$ , where $B$ is at half of the height of the glass.
• Then, Beatrice drinks until the water surface is connecting points $A$ and $C$ , where $C$ is at the circumference of the base of the glass.
• Then, Carl drinks until the water surface is connecting points $A$ and $O$ , where $O$ is the center of the circular base.
• And David drinks the rest.

Who drinks the largest amount of water?