The unaccounted volume of water due to leakage and seepage throughout the distribution network, from the point of origin to the point of consumption, was measured in Chalous-Iran.  Twelve wells and one spring were the sources of drinking water to 17,500 consumers. The 250 km network served a 2000-hectare area.  The twelve wells provided 9,095,074 m3 annually. The investigation considered contributing factors to the loss of water due to leakage and seepage, including the age of network, the flow pressure, construction materials, and mechanical failure of the pipes, valves and outlets. The estimated loss due to leakage and seepage was 3,906,115 m3 annually.  The loss increased with the age of the network. The oldest segment of the network that covered a 248-hectare area aged 30 to 35 years. The greatest service area of 534 hectares aged 20 to 25 years.  The pressure flow ranged between 1 to 6 atmospheric pressure at different locations throughout the network.  An increase in pressure flow resulted in more frequent incidents of leakage and seepage in the segment of the network aged 25 years and beyond