Evaluation of water harvesting potential in residential houses of arid regions (case study: Mashhad, northeast of Iran)

In this research, harvesting of water from a home-scale combined system consisting of rainwater from roof catchment and also relatively clean waste water in the second sink of the kitchen has been evaluated. After installation of the required equipment and preparation of the system, process of rainfall-runoff and the volume of harvested water from each source (roof catchment and the kitchen second sink) as well as its quality were separately measured regularly every month, and for the whole year. Results showed that the harvested water considerably varies in different months mostly due to large variation of monthly precipitation which is common in the research area. Mean runoff coefficient in the roof catchment which was measured in different precipitation events was 0.73. The annual value of water harvested during the research period which was a dry year (annual precipitation about 20% less than the long-term annual average) was 36.78 m3. However, based on the obtained runoff coefficient, the volume of harvestable water in a normal year is 42.292 m3. From this volume of water, 69.6% is provided from the roof catchment, and the remaining 30.6% belongs to the second sink of the kitchen. This water covered 27.1% of the water used during the year by the family of four people. The results of the quality analysis showed that harvested water has no problem for the non-drinking uses of households. Although, the values of quality parameters vary in different months, but only real color (in most of the times) and Mg (in three months) are higher than the upper limit of the drinking water standards.