This paper investigates the applicability, reliability and economic benefit of rainwater harvesting (RWH) systems to partially offset the daily water demand in the multistoried residential buildings in combination with the town water supply systems in Dhaka city. A comprehensive computer software was developed with a view to assessing the reliability and feasibility of the RWH systems in an urban setup. The software was developed using daily water balance modelling concept, which uses input data like daily rainfall, roof catchment area, runoff losses and tank volume. Three distinct climatic scenarios, i.e. wet, average and dry years were chosen by analysing historical 20-years daily rainfall data. Typical residential buildings of plot size 2.5-5.0 katha (168-335 m(2)) were considered for the study. Results indicated that about 15-25% reliability can be achieved under the wet climatic condition and for catchment sizes varying from 140 m(2) to 200 m(2), 250 kL to 550 kL of rainwater can be harvested each year. Several reliability curves have been presented for two roof catchment sizes (140 m(2) and 200 m(2)) under three climatic scenarios and an insignificant increase in the reliability of the RWH system beyond the tank volume of 30 m(3) was observed. The current underground tank sizes of the residential buildings are sufficient to prevent the potential overflow during monsoon. A monetary saving of around 2000 BDT can be achieved for the catchment size of 140 m(2) with tank size of 40 m(3) under average year climate condition and the monetary saving increases with increase in catchment size. (C) 2015 Elsevier B.V. All rights reserved.