From what I've read, Britta pitchers are a common source of roommate contention. I'd just rig up a filter on the kitchen sink, but it's "Not allowed" so we have one of those rectangle britta pitchers in the fridge, which only I fill.
Mom asks for water, the son of a madam is empty.
So I fill it, and wait for the water to process.
Roommate swoops in to snag first glass, and I told him no, mom asked first.
Eh, he backed down, but still, holy poo.