To determine the rainwater capture potential in a small residential city located in semiarid Southern California, a model of the city's existing storm drainage system was developed using a watershed management model based on the U.S. Environmental Protection Agency's storm water management model. The model analyzes the effect of (1) 2- and 10-year 24-h storms and (2) dry, average, and wet climatic conditions under five different scenarios, considering (1) single rain barrel, (2) 5 rain barrels, (3) 7 rain barrels, (4) 10 rain barrels, and (5) a storage tank in each residential lot. Results show that, due to its fixed capacity, rain barrel(s) can only save a limited amount of water. A storage tank per lot increases rainwater capture efficiency, which can collect 19% of city's annual reclaimed water volume in an average climatic year. However, storage tanks can only be cost-effective to residents through financial supports from local agencies.