What do you think about me being that roommate that only fills my own water bottle up just enough so that I never have to refill the water filter?
Why would you be so stingy?
I hate having to refill the water filter, it sucks.
Whenever you use a communal water filter, you should fill it up for the next person.  It sounds like the effort you put into being stingy is just as much trouble as it would take to be considerate of others.
Why should I do that?
It is considered by many to be rude and inconsiderate to not refill the water filter after you've used it. Imagine if you went to get that little bit of water to pour and it was empty because everyone else acted like you?