The Organization had its beginning as a sub department under the Public Works Department, for Water Supply & Drainage. In 1965, it became a division under the Ministry of Local Government. From 1970, this division functioned as a separate department under the Ministry of Irrigation, Power & Highways and remained so until the present Board was established in January 1975 by an Act of Parliament.

The National Water Supply Drainage Board (NWS&DB), which presently functions under the Ministry of Water Supply & Drainage is the principal authority providing safe drinking water and facilitating the provision of sanitation in Sri Lanka. In accordance with the NWSDB Act, a number of major Urban Water Supply Schemes operated by Local Authorities were taken over by the NWSDB to provide more coverage and improved service. Consumer metering and billing commenced in 1982. Rural Water Supply & Sanitation programmes including deep well programmes are also being implemented by the NWSDB.

During the past years, the organization has considerably expanded its scope of activities.

The NWSDB is presently operating 334 Water Supply Schemes in the island which covers more than 50% of the total population with pipe borne water supply. Currently the organization serves 2.8 Million connections with expected expansion in the years to come. The NWS&DB is also in charge of the sewerage system in Colombo and suburbs, Hantane, Koggala, Hikkaduwa, Kataragama and in few housing schemes.