Abstract: An apparatus and method for capturing filtered rainwater during wet weather, storing the filtered rainwater in an elevated storage tank, conveying the filtered rainwater by gravity to a toilet tank and controlling its introduction into the toilet tank. The apparatus preferably comprises an inline filter for installation in a horizontal or sloping section of a rain gutter, a storage tank that is mountable at an elevation higher than the elevation of the toilet tank, water transfer tubing or piping for conveyance of filtered rainwater to the storage tank, water supply tubing or piping for conveyance of stored water to the toilet tank, and a control valve for introducing the stored water into the toilet tank when it is needed. In a preferred embodiment, the components of the apparatus are provided to the consumer in the form of an easily installed kit.