When I'm riding (all road, never trails) I leave the tip on my water bottle shut. When I take a drink, I pull the tip open with my teeth, squirt some water, and then bump it against my slightly-opened teeth to shut the tip again.
I do it because the tip of my bottle will often get dirty, and I'll have to wipe it off with my shirt before drinking. If I leave it open grime would get inside the tip of the bottle.
It is a bit tedious, but I'm now used to it. Is this standard practice?