Falling water table a looming danger

Falling water table a looming danger

Extensive use of groundwater for irrigation, domestic use as well as industrial purposes has been an issue of huge concern since long in Bangladesh. But no serious effort has so far been made to reduce the country's dependence on groundwater. Dhaka, for instance, one of the megacities of the world with around two million people is highly dependent on groundwater. Around 75 per cent of the city area is covered by the Dhaka Water Supply and Sewerage Authority (DWASA). But the water it supplies to the city's households comes from groundwater. 

 A study has shown that Dhaka's groundwater level is declining at an alarming rate of two to three metres per year in the densely populated central part of the city. On the outskirts of the city, on the other hand, the declination rate is much less. The reason, obviously, is that the rate of recharging of the aquifer is higher there. Needless to say, rainwater, existing wetlands and lower population density have contributed to comparatively less withdrawal of groundwater from those parts of the city. But the way the city is expanding with uncontrolled grabbing of the wetlands around it, it is feared that these areas will soon be exposed to the risks similar to central Dhaka so far as the drop of water table is concerned.  

However, the picture of the groundwater situation is no better in the remaining part of the country, either. A study report published in 2018 in the Elsevier journal Science of the Total Environment showed that between 2003 and 2013 the storage level of groundwater in the country fell by 32 per cent. The study further found that the water table was falling by 8.73 milimetre a year during that period. What does this imply for a country that is on the frontline of climate change-related hazards? A country known for the abundance of rain and surface water in its numerous rivers, canals, lakes and marshes has now 75 per cent of its irrigated agriculture depending on groundwater! Worse yet, 90 per cent of the country's water use is dedicated to agriculture. And the use of groundwater is intense during the hot season from March to November. These hard facts should leave a sobering effect on the people who are supposed to look after the planning and management of water use in the country.  

With a growing population, which is projected to be 220 million by 2050, according to UNFPA, Bangladesh is facing a huge challenge so far as its food security is concerned. This is for the simple reason that its groundwater-based agriculture will soon find water from its existing deep tube-wells drying up as the water table has gone down further. A report published recently in the media says that the groundwater levels in Dhaka, Chattogram, Khulna, Sylhet, Rajshahi, Barishal, Tongi, Gazipur and Naryanganj have been declining at an alarming rate. In some cases, it requires more than 200 feet of boring below the earth's surface to find any trace of water. 

The falling of water table is not purely a Bangladeshi phenomenon. In fact, the same is happening across the globe. As humanity did with other vital resources like fossil fuel that Mother Nature has been preserving underground for millions of years, so did it also with groundwater. With the invention of drilling technology to bore holes deeper below the ground, the groundwater became another victim of modern humans' mindlessness. Thus did the gratuitous boring of the soil start everywhere in search of cheap fresh water. Small wonder that this global reserve accounting for 99 per cent of the earth's fresh water is now under threat of depletion. Uncontrolled extraction of fossil fuel and its use along with destruction of forests have triggered global warming, a looming threat to the life on earth. But what about the constant depletion of the earth's freshwater reserve, groundwater?  

True, less developed countries with large populations to feed will be the first to come in the line of fire. But there is no room for complacency for the more privileged nations of the world unless measures are taken to wean away from the habit of using groundwater.  

In fact, the alternatives are there. Conservation of surface water is a time-tested way in this direction. There was a practice in this part of the world in the days gone by to dig ponds. Moneyed philanthropists would dig big ponds and lakes for common use of the public. Though, generally speaking, there was no shortage of water in those days, people were still very cautious as well as economical about the use of water. But in modern life they are no more so. In the urban centres of the world, careless use of piped water is another example of how irresponsible we have become in our attitude towards water.  

There is, however, no denying that the popularity of groundwater for drinking purpose had to do with the prevalence of pathogens in surface water that cause infectious diseases like diarrhoea, cholera, typhoid. But that groundwater is also not without its flip side has become evident from the existence of toxins, especially arsenic, in tube-well water. With the technology now in hand to free surface water of harmful pathogens, there is no reason why we cannot reduce our overdependence on groundwater for drinking. Similarly, a more pragmatic policy of water management through harvesting rainwater and undertaking a nationwide water conservancy programme can and should reduce agriculture's dependence on groundwater to a great extent. These steps are vital for the nation's existence. 

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