DWR is durable water repellent. This is a fluoropolymer based coating that is applied to the outer face of a fabric in the factory. It is applied to a waterproof garment to prevent the outer fabric from water saturation.
If the outer layer of a waterproof garment becomes saturated (wetted out) then this seriously effects the waterproofness and breathability of the other layers in a waterproof breathable fabric like eVent.
DWR coated fabrics need frequent reproofing because the DWR wears of and is effected by 'dirt'. When water is no longer 'beading' on your waterproof garment in requires reproofing.