Groundwater depletion and pollution

Posted: 26 March 2008

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.

Groundwater aquifers are being over-pumped nearly everywhere. Increasingly, they are also becoming more polluted, mostly with chemical runoff (fertilizers and pesticides) and animal wastes from agriculture.

imageClick here for illustration showing 'Types of Aquifers, Wells and Groundwater Flow'

Agriculture is responsible for most of the depletion of groundwater, along with up to 70 per cent of the pollution. Both are accelerating.

Many of the world's most important grainlands are consuming groundwater at unsustainable rates. Collectively, annual water depletion in India, China, the United States, North Africa and the Arabian Peninsula adds up to a hefty 160 billion cubic metres a year - an amount equal to the total annual flow of two Nile Rivers.

The Ogallala Aquifer, which feeds irrigated agriculture in eight US High Plains States demonstrates the problem. This aquifer, because it is so deep, gets very little replenishment from rainfall. Currently, the aquifer is being depleted at a rate of some 12 billion cubic metres a year. According to water expert and author Sandra Postel, the total depletion to date amounts to some 325 billion cubic metres, a volume equal to the annual flow of 18 Colorado Rivers.

India and China fare little better:

  • Surveys in northern India found that water tables are dropping 0.6 to 0.7 metres a year in parts of Haryana State and half a metre a year across large areas of Punjab. In the State of Gujarat, on the northwest coast, 87 out of 96 wells monitored showed significant groundwater depletion during the 1980s and early 1990s. However, according to the International Water Management Institute, 25 per cent of India's harvest is threatened by unsustainable groundwater use.

  • In northern China groundwater depletion has reached catastrophic levels. Across the northern half of the country, groundwater over-pumping amounts to some 30 billion cubic metres a year. China's northern and central plains produce roughly 40 per cent of the country's grain. Across a wide area of this region, water tables have been dropping between 1 and 1.5 metres a year for a decade, even as water demands continue to rise.
Groundwater is becoming more polluted, as it becomes more depleted. Europe is no exception. Within 50 years some 60,000 square kilometres of groundwater aquifers in western and central Europe could well be contaminated with pesticides and fertilizers. There are two examples:

  • Currently, of Hungary's 1,600 well fields tapping groundwater, 600 of them are already contaminated, mostly with agricultural chemicals.
  • In the Czech Republic 70 per cent of surface and ground waters are polluted, mostly with agricultural and industrial wastes.
In India and Bangladesh, millions of people are exposed to groundwater contaminated with high levels of arsenic, a highly toxic and dangerous pollutant. It has been estimated that close to 5 million people in West Bengal, India are affected. In next-door Bangladesh, half the entire population of 120 million are exposed to elevated levels of arsenic in their drinking water.

See: Threat of mass arsenic poisoning in Bangladesh.