The Wainuiomata-Orongorongo catchment area began chlorinating its water supply in 1963.
Following the Boxing Day flood in 1962, intense rainfall in the Wainuiomata and Orongorongo valleys inflicted damage on intake weirs, resulting in the transport of mud and silt into the city before the valve could be closed. Consequently, in 1963, the construction of a chlorination plant commenced to address both water supplies. Permanent chlorination and fluoridation facilities were then completed by 1964-65. Strainers were subsequently installed on the O-K main in 1967 and the Wainuiomata pipe in 1968.
