Two key sources of potable water for Mumbai - Tansa and Modak Sagar lakes - started overflowing on early Thursday due to heavy rains in their catchment areas since last week, the city civic body said.

With this, four lakes that provide drinking water to the metropolis are now filled to their capacity. The Brihanmumbai Municipal Corporation (BMC) said the Modak Sagar lake started overflowing at 3.24 am and Tansa at 5.48 am.