Being able to 3D print a water bottle would be super cool, so I'm going to show you how to create the model!
I'm going to show you how to make a 3D printable water bottle using Autodesk 123d Design desktop version! It's awesome, download it here http://www.123dapp.com/design
After thinking through several water bottle designs, I concluded that doing it this way is one way to make it 3d printable without having a screw on top. The two plugs on the top block two holes: One for drinking from, and another larger one to make cleaning the bottle more convenient. Due to the small decrease in the size of the plugs in relation to the holes, being a fraction of a millimeter smaller, the plugs should fit snuggly. I attached an stl. file with the design.
It's in separate pieces in the model, so that you can print it then put it together
First, download 123d Design, start a new project, and change your units to centimeters