Effects of rainwater-harvesting-induced artificial recharge on the groundwater of wells in Rajasthan, India John M. Stiefel & Assefa M. Melesse & Michael E. McClain & René M. Price & Elizabeth P. Anderson & Narendra K. Chauhan Abstract In light of the increasing deterioration of ground- water supplies in Rajasthan, India, rainwater harvesting practices in southern Rajasthan were studied to determine the effects of artificially recharged groundwater on the supply and quality of local groundwater. A physical and geochem- ical investigation utilizing environmental tracers (δ 18 O and Cl – ), groundwater level and groundwater quality measure- ments, and geological surveys was conducted with two objectives: (1) to quantify the proportion of artificially recharged groundwater in wells located near rainwater harvesting structures and (2) to examine potential effects of artificial recharge on the quality of groundwater in these wells. A geochemical mixing model revealed that the proportion of artificial recharge in these wells ranged from 0 to 75%. Groundwater tracer, water table, and geological data provided evidence of complex groundwater flow and were used to explain the spatial distribution of artificial recharge. Furthermore, wells receiving artificial recharge had improved groundwater quality. Statistical analysis revealed a significant difference between the water quality in these wells and wells determined not to receive artificial recharge, for electrical conductivity and SO 4 – . The findings from this study provide quantitative evidence that rainwater harvesting structures in southern Rajasthan influence the groundwater supply and quality of nearby wells by artificially recharging local groundwater. Keywords Rainwater harvesting . Artificial recharge . Water quality . Tracer tests . India Introduction With changing climate and growing levels of water consumption, increasing seasonal variability and steady declines in groundwater levels pose a problem of access to reliable water supplies for many of India’ s rural inhab- itants. Rajasthan, one of India’ s driest states, relies on groundwater for 90% of its drinking water supply and 60% of its water for irrigation (ECIDWR 2005). This heavy dependence on groundwater arises from sparse surface water supplies. Rajasthan is India’ s largest state, with more than 10% of the country’ s geographic area and 5% of India’ s population, yet it contains only 1% of the nation’s total surface water resources (GOR 2005). Overexploitation of groundwater resources throughout the state has led to only 32 of the 236 “blocks” (sub- districts) in Rajasthan to be considered safe with respect to groundwater consumption (Sharma and Roy 2003). In recent decades, rainwater harvesting (RWH) has been promoted as a solution to the overexploitation of the Rajasthan’ s groundwater resources (Kumar et al. 2005). Rainwater harvesting is defined as the collection and Received: 12 July 2008 / Accepted: 28 May 2009 Published online: 24 June 2009 © Springer-Verlag 2009 J. M. Stiefel ()) : A. M. Melesse : M. E. McClain : E. P. Anderson Department of Environmental Studies, Florida International University, 11200 S.W. 8th Street, University Park Miami, FL 33199, USA e-mail: stiefel.john@gmail.com Tel.: +1-206-5509495 Fax: +1-305-3486137 A. Melesse e-mail: melessea@fiu.edu M. McClain e-mail: michael.mcclain@fiu.edu R. M. Price Department of Earth Sciences and Southeast Environmental Research Center, Florida International University, 11200 S.W. 8th Street, University Park Miami, FL 33199, USA R. Price e-mail: pricer@fiu.edu Present Address: J. M. Stiefel World Vision, P. O. Box 9716, MS 446 Federal Way, 98063 WA, USA Present Address: E. P. Anderson The Field Museum of Natural History, 1400 S. Lake Shore Dr., Chicago, IL 60605, USA e-mail: eanderson@fieldmuseum.org N. K. Chauhan Department of Geology, Mohan Lal Sukhadia University, Udaipur, 313001 Rajasthan, India e-mail: nkcgeol54@yahoo.com A. M. Melesse M. E. McClain R. M. Price Hydrogeology Journal (2009) 17: 2061–2073 DOI 10.1007/s10040-009-0491-6