Background: Groundwater depletion, Indo-Gangetic aquifer, Gravity Recovery and Satellite Experiment (GRACE).
- The gravest threat to groundwater in India is not over-exploitation but arsenic and salt contamination.
- This is the conclusion of a new study which also challenges several recent reports to say that 70 percent of the water table in most of the Indo-Gangetic aquifer (among the largest in the world) is stable and mostly improving.
- The authors of the study say the unsustainable levels of groundwater extraction are largely limited to urban agglomerations in Punjab, Haryana and Uttar Pradesh.
- However, the study says that nearly 23 percent of the 300 BCM (billion cubic metre) is extremely saline and about 40 percent contaminated by arsenic.
- In recent years, several reports have warned of alarming groundwater depletion in northwest India and Pakistan based on satellite imagery from the Gravity Recovery and Satellite Experiment that has minutely tracked how gravity varies across the earth since 2002.
- The researchers sought to assess groundwater-level variations, groundwater quality and groundwater storage within the top 200 m of the Indo-Gangetic aquifer.
- Canals built in the 19th and 20th centuries significantly influenced groundwater trends, the study says as water accumulated at the origins of the canal tended to leak out, leading to high recharge and sometimes floods.
- Moreover, geological variations determine how much groundwater is available in a region and only regular groundwater observations would give an accurate picture of water availability.