Groundwater

About 2 billion people, approximately one-third of the world's population, depend on groundwater supplies, withdrawing about 20 per cent of global water (600- 700 km³) annually - much of it from shallow aquifers (UNDP and others 2000). Many rural dwellers depend entirely on groundwater.

The issues of groundwater use and quality have until recently received far less attention (particularly in some developing regions) than surface water, and data on groundwater stocks and flows are even less reliable. However, in Europe, much attention has been paid to groundwater quality because many settlements depend on such resources for water supply. Generally, groundwater resources are vulnerable to a variety of threats, including overuse and contamination (see table below).

Groundwater quality problems
Problem	Causes	Concerns
Anthropogenic pollution	Inadequate protection of vulnerable aquifers against human-made discharges and leachates from: urban and industrial activities; intensification of agricultural cultivation	Pathogens, nitrates, ammonium salts, chlorine, sulphates, boron, heavy metals, DOC, aromatic and halogenated hydrocarbons nitrates, chlorine, pesticides
Naturally occurring contamination	Related to pH-Eh evolution of groundwater and dissolution of minerals (aggravated by anthropogenic pollution and/or uncontrolled exploitation)	Mainly iron, fluorine and sometimes arsenic, iodine, manganese, aluminium, magnesium, sulphates, selenium and nitrates (from paleo-recharge)
Well-head contamination	Inadequate well design and construction allowing direct intrusion of polluted surface water or shallow groundwater	Mainly pathogens
Source: Foster, Lawrence and Morris 1998

When use exceeds natural recharge over a long period, groundwater levels drop. Parts of India, China, West Asia, the former Soviet Union, the western United States and the Arabian Peninsula are experiencing declining water tables, limiting the amount that can be used and raising the costs of pumping to farmers (Postel 1997, UNEP 1999). Overpumping of groundwater can lead to salt-water intrusion in coastal areas. In Madras, India, for example, saltwater intrusion has moved 10 km inland, contaminating wells (UNEP 1996).

Concern over growing problems related to groundwater resources has galvanized the international community, governments and other stakeholders to start addressing them. For example, the Second World Water Forum in March 2000 organized a special workshop on groundwater. Some of the recommendations arising from the workshop included the need to raise public awareness and 'improve information availability, quality and accessibility to stakeholders, technical specialists and policy-makers' (World Water Forum 2000).