The Size 3 KAP7 HydroGrip Water Polo Ball is the Official Ball Size for Boys and Girls 12 and Under Water Polo. KAP7 has quickly become the go-to choice for amateur and elite water polo players alike. KAP7 has tapped into years of experience, proprietary technology, and the highest quality materials to develop the HydroGrip Ball. It is the best and longest lasting ball in the world. The HydroGrip has been designed to meet guidelines for local, national, and global specifications.