In cities with problems of aridity and a shortage of drinking water supply, there is an urgent need to establish alternatives for an adequate water management program. This study proposes an estimation through which users can select a rainwater harvesting system for non-drinking water consumption. For the cities of Pachuca and Mineral de la Reforma, State of Hidalgo, Central Mexico, the historical record of rainfall analyzed covers a period of 33 years (1980-2013). We calculated the monthly volume of rainwater harvestable from roof areas (VR, m(3)) with household roof areas (Hra) of 45 m(2), 50 m(2), 100 m(2) and 200 m(2). It is proposed to replace in each single house the flush toilets and washing machine with ecological devices with consumptions of 4.8 L/flush and 70 L/load, respectively. Furthermore, a maximum and a minimum consumption of eight and six flushes/day/person (flush toilets) and five and four loads/week (washing machine), respectively, are proposed. From these considerations, our estimations of the harvestable rainwater showed that households with Hra of 45 m(2) and 50 m(2) would depend on the water supply system of the public network during part of the year. On the other hand, households with Hra of 100 m(2) and 200 m(2) might be able to store enough water to meet other needs besides toilet flushing and laundry.