1st off, never offer things that you cant provide,this is not what you wanna be doing every weekend. But thats what they do on porn sets when you cant squirt or piss. when your ready grab your,closely placed, water bottle and squirt some water up there and rub your pussy like your trying the start a fire as you push it out. You can edit and make things look any way you want, if youre techie enough you can create the splashing water in a glass separately and just overlay on top of your image.
If it was me, i'd drink enough water till my piss was clear and "squirt" in the cup, mean while I'd have a fresh glass of water off cam that I will grab and make that edit magic happen.