A quick and easy way to detect groundwater in semi-arid（干旱的） hard rock areas that is also economical could improve the siting of borewells to improve clean water supply in the developing world. Details of the approach are outlined in the International Journal of Hydrology Science and Technology this month. P.D. Sreedevi, Dewashish Kumar and Shakeel Ahmed National Geophysical Research Institute in Hyderabad, India, explain how electrical conductivity (EC) logs of hard rock terrain¹（地形，地势） recorded before and after the monsoon² season can reveal differences that show where water accumulates most in subterranean³ rock fissures⁴. By comparing the data with other geological measurements and drilling experiments, the team is available to correlate the EC data with regions of underground water without additional test drilling.

Understanding hard rock aquifers⁶（蓄水层） relies on hydrology（水文学） of fractured rock and knowing details of the subterranean environment. Data is commonly obtained through drilling test boreholes or investigating underground openings. Such work is hazardous⁷ and time consuming and does not necessarily reveal the most appropriate site to sink a water well. However, anomalies in electrical conductivity measurements of which many have been made in various regions might be useful in finding the most abundant sources of groundwater.

The researchers demonstrated how effective the approach might be in correlating information from 25 boreholes in the Maheshwaram watershed⁸ situated⁹ in the Ranga Reddy district of Andhra Pradesh, India, about 30 kilometers south of Hyderabad, covering an area of about 60 square kilometers. The area is semi-arid with average annual rainfall of 750 millimeters. The bedrock is mostly granite¹⁰（花岗岩） . The team points out that, based on the detailed¹¹ geological and hydrogeological studies, the aquifer⁵ is classified as a two-tier coupled system with weathered and fractured layers that exist over almost the entire area. However, due to over-exploitation, the groundwater levels have affected¹² the weathered layers and groundwater flow is currently in the fractured rock aquifer. There are no rivers feeding the aquifers so the system relies on the monsoon to for replenishment¹³（补充） .

"Our approach is fast and cost effective and could be very useful as a screening tool prior to conducting hydraulic¹⁴（液压的，水力的） testing and water sampling," the team concludes.