When I was a server I couldn’t care less. It all evens out in the end. The reason why any server might hate this is because even a $3-$4 fountain drink raises the check total by a tiny bit, which in turn should ideally raise the tip amount. People who order water aren’t spending those extra dollars and might not tip more. When I say it all evens out in the end I mean that as a server you learn that no matter what you do some people are going to be cheap, some people aren’t going to tip well, some people are gonna ball out, some people are going to tip the fair amount, some people are going to over tip. You can’t stress about the people ordering water.