This is of particular concern where groundwater provides a major share of drinking water supplies for both human and the farming sector (Chapter 9 and OECD, 2010a). Water stress is based on the ratio of total water withdrawals (across all uses in the economy, including agriculture) to total annual renewable freshwater availability. For most OECD countries this ratio is low and below 10%, but some countries are experiencing medium water stress above 20%, where water supply and demand needs to be managed to resolve conflicts between competing uses (OECD, 2010a).