Mumbai water supply comes from six lakes -- Tansa, Modak, Bhatsa, Vaitarna, Tulsi, Upper Vaitarna, and Powai. This system is made up of reservoirs, storage, pipes and taps.
The water distribution system in Bombay is also about a 100-years-old. Water is brought in from the lakes after treatment, and stored in 23 service reservoirs. The two major sources, Tansa and Lower Vaitarna, are at a higher level than the city, not much power is required to pump the water.
The service reservoirs are mainly on hills located at Malabar Hill, Worli Hill, Raoli, Pali Hill, Malad, Powai and Bhandup. The timing of water supply to different parts of the city varies between two to five hours.
(picture taken by Kaushal Karkhanis http://www.flickr.com/photos/kaushal/172182002/in/pool-84638485@N00?#comment72157594481695010)