Drinkable tap water project has been broght into operation since  1997. In 1999, Mahidol University in cooperation with the MWA, carried out the inspection of tap water quality in various zones, covering the whole areas of water distribution. It is found that the tap water quality fully meets the World Health Organization criteria and standard. This results in the official announcement of drinkable tap water in 10 areas of branch office, namely Prachachuen, Nonthaburi, Bangkhen, Lat Phrao, Phasicharoen, Taksin, Bangkoknoi, Sukhumvit, Prakanong and Samut Prakan, on May 24, 1999, which added to the previously announced area of branch office : Phayathai on June 5, 1997, Tungmahamek and Mansri on April 27, 1998. As a result the tap water in all distribution areas of MWA's branch offices is absolutely safe for drinking.

       The important cause to worsen the tap water quality was the rusted old pipes within the comsumers' houses. From the inspection carried out by Mahidol University, it was found that 29.3 percent of the customers used water pumps, and 17.1 percent of these people pumped water directly from the pipes. The main activity of the MWA is to try to give as much knowledge and understanding as possible to make the consumers  accept the responsibility for pipe repairs or replacement within their own houses, for cleaning the reservoirs more frequently, and for using the water pumps in the correct way. In order to assure the consumers about absolute drinkable tap water, the MWA has to give an example first by setting up a clean-up program to carry out the pipes and reservoirs inspection and improvement in every buildings within its own organization. After the success of quality analysis test, and all the employees turning to drink tap water, it was officially announced that the pipes were of high quality suitable for drinkable water.