Abstract: A rainwater harvesting prefilter having a filter drum. The filter drum includes a fluid inlet configured to be fluidly connected to a fluid entrance pipe of a rainwater collection system and a fluid outlet configured to be fluidly connected to a cistern tank. A filter assembly is disposed in the filter drum. The filter assembly includes a filter support plate (with supporting components as needed) suspended in the filter drum such that the filter support plate spans across and substantially covers a width of the filter drum to separate the filter drum into an upper chamber having the fluid inlet and a lower chamber having the fluid outlet. A plurality of spaced-apart apertures are disposed in the filter support plate. A plurality of filter socks are positionable in the plurality of spaced apart apertures such that filter socks extend downward from the filter support plate into the lower chamber.