Roommate wasting water?

I don't think im a tree hugger, but my roommate wastes a lot of water. even in the bathroom our sink is kinda messed up so if you don't turn it off completely (which takes minimal effort of your arm muscles), little bit of water continues to run. So I tell him to not waste water and his response is "water is free" (meaning we dont pay water bill)......which pisses me off so much. We get in fights sometimes for this crap. Should I just ignore it or keep telling him to not waste water.