Grey water irrigation is another technique used to filter grey water and help recharge ground water reservoirs. The process entails using a sand and gravel filter to filter out some of the particulate. After filtration, the water is drained into a pump pit. From the pump pit, the grey water is pumped through an irrigation system for further purification by plant roots. The potassium, nitrogen and phosphorous in the grey water acts a fertilizer, saving the consumer money and preventing the need for petroleum based fertilizers.