Abstract: This paper proposes a new method to evaluate junctions' water demands in pipelines system by classifying users' demands patterns. Further more, GIS (geographic information systems) spatial analysis technique is applied in accessing customers' water payment data from utility' s billing database so that customers' base demand and junction water demand can be calculated. A solution is given for computing unaccounted for water including leakage losses, water supplying and water demand's computational value are adjusted to balance . Finally a real engineering demo is presented.