Another source of water are sprinkler systems. The systems are large pipe and hold large volumes of water. Some times the water tends to be the next thing to oily pond scum so I wouldn’t try it unless the building was fairly new and the water was for other than drinking. Sprinkler systems have a 2″ drain pipe at the control valve that exits the building adjacent to the valves. One person could open and close the valve while the other collects the water.