eak acid cation (WAC) resin plays an important role in water treatment. It is usuallymanufactured from acrylic acid and divinyl benzene (DVB) as a crosslinking agent, although some manufacturers make it from methacrylic acid or its derivatives. It is awidely used unit in demineralisation plants for dealkalisation of water. The total capacityof WAC resin at 210 gl as CaCO3 is higher than other ion exchange resins. The resin isregenerated with dilute acid using near stoichiometric quantity. Hence, the waste watergenerated during regeneration is almost neutral. WAC resin operates in a alkaline pHrange and exhibits large volume change when converted to different forms. Hence, it iscalled the workhorse of water treatment processes.