The Hidden Water Crisis Beneath The Sundarbans: Today’s Reality, Tomorrow’s Water Security

By – Mijanur Mondal and Dr. Kousik Das

Department of Environmental Science and Engineering, SRM University-AP, Amaravati,

Freshwater is becoming increasingly difficult to rely on—even though the Sundarbans is surrounded by water. The region is crisscrossed by rivers, tidal creeks and channels, but much of this water is saline. For communities that depend on groundwater, the problem is less visible: water drawn from beneath the ground can also be vulnerable to surface pollution and salinization. This combination of salinity and pollution is creating a growing water-security challenge for the more than forty-five million people living in the Indian Sundarbans.

But what is happening beneath the surface? Is groundwater becoming contaminated from activities on land, or is saline water moving into the aquifers from the surrounding tidal waterways?

A recent study of groundwater in the Indian Sundarbans conducted by Dr. Kousik Das and his PhD scholar Mr. Mijanur Mondal of SRM University-AP which published in an internationally reputed journal Science of the Total Environment (Mondal et al., 2026) suggests that the threat to groundwater in the Sundarbans is not coming from a single direction. The researchers combined groundwater chemistry, nitrate measurements, stable isotopes and spatial vulnerability mapping to understand how different processes affect groundwater across the region. Rather than treating groundwater vulnerability as a single problem, the study examined both the downward movement of contaminants from the land surface and the lateral influence of saline water.

The findings reveal a highly variable groundwater system. About 79% of the assessed area falls within moderate or high groundwater-vulnerability categories. The research unveiled that about 79% of the Sundarbans’s groundwater is categorized as moderate to high vulnerability. However, the level of groundwater vulnerability varies from coastal areas to further Inland regions (especially parts of Basanti, Jaynagar, Gosaba, Hingalganj, Canning and Hasnabad C. D. Blocks). These areas are more prone to surface contaminants moving during groundwater recharge from the land surface. Human activities including unscientific irrigation, agricultural practices, groundwater over-abstraction plausibly led this surface contamination to eventually reach into groundwater. In contrast, areas influenced by tidal creeks and coastal waters, (such as Gosaba, Sagar, Patharpratima and Kakdwip C. D. Blocks) are more susceptible to the lateral influence of saline water.  Therefore, the study suggests that the groundwater crisis and insecurity in the Sundarbans cannot be explained simply by saying that contamination comes from the surface or that salinity comes from the sea. Both processes can operate, depending on the local hydrogeological setting.

Nitrate measurements provide another piece of evidence. Higher groundwater nitrate occurrence was recorded associated with agricultural areas even in deep groundwater too which is a critical health concern for the communities. The distribution broadly corresponded with areas identified as more vulnerable to surface derived influence. Because large sections of the population entirely depend only on fresh and deep groundwater for drinking needs. In contrast, salinity tells another part of the story. Groundwater salinity varied substantially across the Sundarbans, ranging from 0.70 to 8.90 PSU (Practical Salinity Unit). Inland blocks recorded the highest groundwater salinity range, while surprisingly coastal areas had lower salinity. But one of the study’s notable findings is that depth also matters. In some coastal areas, groundwater does not necessarily become saltier as one goes deeper. Deeper groundwater near the coastal blocks (especially Sagar, Kakdwip, and Namkhana) at depths of around ~300 meters below ground level, was comparatively fresh, with salinity around 1 PSU, while shallower groundwater in these areas could be considerably more saline. Dr. Das further collaborated with Prof. Abhijit Mukherjee and Mr. Somdipta Sen of IIT Kharagpur to integrate Stable Water Isotopes in this study, which suggests that groundwater quality is shaped by the interaction between recharge, aquifer characteristics, surface water and saline water rather than by a single process. The researchers also found that land use and land cover and depth to the water table were among the most influential factors controlling vertical groundwater vulnerability. Groundwater abstraction, recharge and aquifer characteristics also contribute to the spatial differences in vulnerability. For saline intrusion, factors such as existing seawater intrusion, groundwater levels and aquifer thickness were important.Beyond these hidden problems beneath the ground, the water crisis is also visible in the daily lives of people in the Sundarbans. In many parts of the region, people often have to travel more than two kilometres on average to collect drinking water. At times, several families have to depend on a single tubewell, highlighting the severity of the crisis (Photo 2). During cyclones, these tubewells can also be damaged or submerged, further disrupting access to freshwater as evidenced from Dr. Das’s recent research.

The findings have implications for how groundwater should be managed in the Sundarbans. A single strategy may not work everywhere. Areas vulnerable to contamination from the surface require greater attention to land use, agricultural activities and recharge zones, while areas exposed to saline influence require monitoring of groundwater levels, abstraction and interactions with tidal waterways. The study therefore points to the need for regular groundwater monitoring in vulnerable hotspots and better regulation of groundwater management practices to better understand how groundwater vulnerability changes over time. The Sundarbans doesn’t simply need more water; it needs better protection of the freshwater that remains.

Research paper reference:Mondal, M., Sen, S., Mukherjee, A., & Das, K. (2026). Lateral and vertical solute transport controlling groundwater pollution in the Sundarbans: Insights from nitrate concentration and stable isotopic signatures. Science of The Total Environment, 1048, 182043.