Introduction

Groundwater is an essential part of the hydrological cycle and is a valuable natural resource providing the primary source of water for agriculture, domestic, and industrial uses in many countries. Groundwater is now a signifi cant source of water for human consumption, supplying nearly half of all drinking water in the world (WWAP 2009) and around 43 percent of all water effectively consumed in irrigation (Siebert et al. 2010). Groundwater also is important for sustaining streams, lakes, wetlands, and ecosystems in many countries.