Rainwater Harvesting
In the context of rainwater harvesting, "first flush (diverter)" refers to a simple device to avoid the first flush runoff contaminating the storage cistern. This leads to a higher quality of water captured, and less silting of the cistern over time in dutsy areas. The first flush water is then generally still utilised 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 pgs 8-9 of for calculations on sizing.
Read more about this topic: First Flush