First Flush Rain Water Diverters helps protect your rain harvesting system by collecting cleaner rainwater. Between rainfalls, roof contaminants and small debris can collect on your roof such as dust, pollens, bird and animal droppings.  Downspout First Flush Water Diverters improve water quality and reduce tank/cistern maintenance. Downspout First Flush Diverters are easy to install at your downspout on the way to the tank.  The First Flush Diverter system uses a ball and seat system within a chamber along the downspout pipe. The first rain water runs into your gutters and down the downspout, when it arrives at the diverter chamber, the dirty water fills the chamber and the ball floats and rises until it settles against the seat and seals off the dirty water while then allowing the clean rain water to flow past into your collection system.