DI water is used extensively in electronics manufacturing. In semiconductor manufacturing it is used for cleaning and etching wafers. DI water is also used in CMP processes and the critical immersion lithography process. Up to 1000 gallons of water is needed to process a single 300mm wafer. Because DI water is used in many critical process steps and directly contacts the wafer, controlling its contaminants is critical to maintaining high yields. On line monitoring of particle levels is a common method of controlling contamination in DI water systems.