Metropolitan Waterworks Authority

In the reign of King Rama V, when Bangkok had a population of roughly 333,000, the king, returning from his first visit to Europe in 1897, ordered the establishment of a Sanitary Department to provide water to the Bangkok populace. Many still used water from rivers or canals, frequently the source of epidemics. The new department made a survey and dug up a distributary canal of the Chao Phraya River at Sam Lae Sub-district in Pathum Thani Province to the north of Bangkok. Water was drawn though this canal into Bangkok to supply cleaner water.

In 1907, the king made a second visit to Europe. He found that most European countries produced clean, adequate water for their people. Returning to Thailand, he ordered the hiring of French experts to conduct a survey and make suggestions on water procurement for Bangkok. On 13 July 1909, the king decreed that the government would provide a modern water supply system for the people of Thailand. He ordered the Sanitary Department to dig and construct canals and install water pumps in order to deliver water to water treatment plants in the Sam Sen Sub-district. Pipes were installed underground to distribute water throughout the Bangkok area, at a cost of over four million baht and five years of construction. The king called the result "Bangkok Waterworks". The first water treatment plant was set up in 1914.

Demand for water in Bangkok increased rapidly, from 10,000 to 13,000 metres3 per day, most of which was consumed at numerous public water spigots. People in the suburbs of Bangkok, with no water supply, carried pots to take water from them, especially in the summer, when the waterworks increased production to full capacity of 28,800 m3 per day, sufficient for the population at the time. The government's emphasis on improving water supplies in Bangkok led to the merging of the Nonthaburi municipality water supply, Samut Prakan's water supply, and Thonburi's water supply with those of Bangkok Waterworks. A new organization called the "Metropolitan Waterworks Authority", a public enterprise under the Interior Ministry, began operations on 16 August 1967.

The MWA draws raw water from two sources: the Chao Phraya River at Ban Krachaeng Sub-district, Mueang Pathum Thani District, Pathum Thani Province and from the Mae Klong Dam in Tha Muang District, Kanchanaburi Province. The water is treated with lime, chlorine, alum, and polyelectrolyte at four water treatment plants—Bang Khen, Sam Sen, Thonburi, and Maha Sawat. MWA's treated water is distributed to its 2,375,490 customers in five regional service areas via 37,700 km of water pipes. The 2018 average tariff for residential customers was 9.99 baht per cubic metre. Total consumption in FY2018 was 1,401.4 million m3. At the end of September 2018, the MWA employed 5,365 persons.