According to the CAG report (2012-13) tabled during the ongoing session of state Legislative Assembly, major factors like leakage of water from transmission lines, distribution lines, underground reservoirs, valves, illegal connections, unmetered supply and dysfunctional or faulty meter are resulting in high percentage of unbilled water.
"Considering the rates applicable to various categories of consumers, revenue lost for unaccounted water, excluding the permissible limit of 15 per cent, works out at Rs 77.37 crore during the year 2012-13 itself," the report said.
The unaccounted water represents difference between the quantity of water that is supplied from the water treatment plants and of the quantity measured at the consumer point.
The report said that as per the guidelines specified by the Union Ministry of Urban Development, the unbilled or unaccounted water should not exceed 15 per cent of the total supply.
One of major reservoirs in the state, Selaulim water supply scheme, located in South Goa and catering to most parts of the state, has 39 per cent unaccounted water out of its total supply.
While two other reservoirs, Opa and Chandel, each has 35 per cent unaccounted water, Dabose water supply in state's north-eastern Sattari taluka, has 43 per cent unbilled water, resulting in the staggering revenue loss annually, the report said.