text: In the context of rainwater harvesting, a first flush diverter is a simple device that is designed to protect a storage cistern from contamination by first flush runoff. This leads to a higher quality of water captured, and less silting of the cistern over time in dusty areas. The diverted first flush water is used for irrigation or other purposes in a fashion similar to greywater. Although many commercial versions are available, these devices are frequently constructed of spare pipe when the cistern is initially installed or thereafter. See Texas Manual on Rainwater Harvesting for calculations on sizing.