Abstract: A water collection system blocks down-pipes to collect water from a roof. A down-pipe (27) is located adjacent a rain water diversion unit (31). The unit comprises a box (36) with the down-pipe (27) fitted to an opening (37) in bottom (38) of the box (36). The gutter (14) has two side-by-side openings (39 and 40), the opening (40) has an overflow in the form of upstanding wall (41) while the opening (39) has a valve plate (42) hinged to the front edge at (43). A pneumatic actuator (44) is used to move the valve plate (42) to the closed position. When the valve is closed, the opening (40) and the upstanding wall (41) serve as an overflow back to the stormwater via the box (36). The tank pipe (17) also has an opening (45) with an upstanding wall (46) which has its upper edge (47) set lower than the upper edge (48) of the wall (41) of the overflow. All down-pipes are fitted with diversion units.