One of the major bottleneck for the water utilities is a large number of water losses in the distribution network system and quantifying of this water loss. This is why this thesis focuses on the development of a model for estimating Non Revenue Water (NRW) in Addis Ababa, especially woreda-07 in the Bole sub city.rnThe method used for the model starts with component of real loss by applying Minimum Night Flow (MNF) data taken at a particular installed District Metered Area (DMA). Analysis of the network system is based on the background leakage and concept of Fixed and Variable Area Discharge (FAVAD) in addition with aggregated bill consumption of the study area.rnBentley Water GEMS hydraulic model is prepared to apply the procedure. Then, calculating network leakage at the minimum hour flow (MNF) and distribution of volumetric consumption at each junction for each time step is carried out. In doing so, for leakage plus volumetric, the model runs until the probable pressure and leakage coefficient is established.rnUsing the coefficient in regard with the demand factor for each hour, leakage at each node and pipes for the distribution network is estimated. Based on these information estimated value of real loss 21.04%, apparent loss 4.74 and NRW 131,522.2 m3/year with 25.8% is found.rnFinally, for a more representation of the network and to perform further analysis regarding of water losses a suitable model environment is created in Arc GIS environment; which can be used as an aid around the study area.rnKey words: water supply network, water loss, leakage, real loss, apparent loss, MNF, NRW, Water GEMS, pressure.