I'm wanting to replace a toilet shutoff valve with a new quarter-turn valve. I've already done the sink shutoff valves in the same bathroom. Yet if I shut off the cold water to the house, I still get flow through the toilet shutoff valve. Why would a house be plumbed such that lines to the toilets seem independent of the main shutoff? Or am I missing something here? Other than cutting power to the well pump, what else can I do?