all your toilet water, taps come from mains ! you only have a top tank if your on a Y plan system (hot water backup)......why the hell would you feed cold water in to be just stood in a tank? that would be bloody horrific, if i were to turn my water off the feed wouldnt get to my bathroom as everything is below thus having no pressure to get upstairs...... n00bs! ask any plumber, all cold water is fed in from the mains. The mains goes upstairs to your tank for it to heat, but you have branches off below the tank to your bathroom for cold. The only place you could have anything like what people are saying is if your in remote areas where theres no feed, like bang in the sticks where you could have a spring or a well.