You didn't apply the pressure as a function of the Y coordinate. Below is how you do that when the water is full to the brim.
Under that pressure load, the material exceeds the yield strength and some plastic strain develops. Is that acceptable in this design?

Follow the recommendation in this warning to eliminate the warning.
Turn off the negative Load Multipliers.
Use Face Meshing to get better quality elements. This mesh exceeds the Student License Limit so I can't solve with it, but if you are on a Research or full license, you can.