The main objective of this thesis is to assess the potential of rain water harvesting practice to solvernproblems of both increasing water demand and storm water in Addis Ababa city. The research isrncarried out based on case-study of Jemo condominium site, from November 2014 to May 2015 that isrnfound in the south western part of Addis Ababa city. The site has about 337 residential blocks with anrnaverage roof area of 286m2 and 50 communal blocks with an average roof area of 216m2 roof arearnand serves for about 9,800 households in which they serve for about 42,140 population.rnA descriptive quantitative study was carried out in order to achieve the objectives of the study. Arnmonthly rainfall data, catchment characteristics, roof material, population data, water consumptionrnand water demand data were collected from primary and secondary sources. People's attitude andrnpractice towards rainwater was also assessed. The collected data was analyzed using different toolsrnincluding samsamwater RWH model, Google earth, rainwater harvester, AutoCAD, MS Excel spreadrnsheets and etc. Calibration and validation of the finding was carried out using appropriaterninstruments.rnBased on the findings the total annual rainfall in an average year is 1219mm. A 6 months of waterrnconsumption data of Jemo I collected from AAWSA Mekanisa branch shows that only 30% of therndemand is supplied to residents by the municipality at private water pipes. The average annual RWHrnpotential at Jemo I condominium site is not enough to fulfill the total water demand at this site.rnHowever, it might still be worthwhile to construct a rainwater harvesting system. With a storagernreservoir of 113400 litres (113.4 m3) for a single building a rainwater harvesting system couldrnprovide about 36% of non-potable demand and RWH can reduce water demand problems by 36% forrnonly non-potable demands and 10% for all domestic demands based on the current AAWSA standard.rnThe total cumulative runoff generation from this site throughout the year is 723,450m3 and thernamount of water that RWH system only from roof tops can harvest could be 90,290.2m3. With thisrnestimation RWH from roof tops at Jemo condominium site can reduce runoff by 12%. Thisrncontributes for sustainable storm water management and best management practices. ThereforernRWH has many benefits once it is applied for any building for sustainable alternative water supplyrnand sustainable storm water management. The big problem here will be the size of storage tankrnshould be big enough since the rainfall is concentrated for limited months which will not be costrneffective but related to other interventions RWH is more cost effective and sustainable than otherrnoptions.rnKey words: Rainwater, Harvesting, water demand, Stormwater, Alternative source, Non potable,rnJemo, Domestic, Urbanization, Condominium, Addis Ababa, Ethiopia