Groundwater is indeed a huge wealth of Bangladesh, but this ample freshwater resource is now at a serious risk of gradual depletion and contamination.

Arsenic, salinity, manganese and iodine. All the chemical-minerals mix in water in proportions lethal for humans, animals and plants alike. But the million-dollar question is: how would we know about the water quality beneath the ground?

No comprehensive water quality assessment was done until recently. But over the last three years, a team of researchers from the Bangladesh Water Development Board (WDB) completed a phenomenal project, generating for the first time a deep knowledge base that is expected to revolutionise the usage and management of groundwater resources.

"It is a remarkable development for all the right reasons," lead researcher and WDB Director Dr Anwar Zahid told The Daily Star recently. 

"We have put together a vast data set, with which water authorities will now be able to devise a strategy appropriate for the use and preservation of the freshwater down below."

Falling groundwater level, rising arsenic level and salinity intrusion in coastal regions are no new news. People came to know about the growing threats in bits and pieces from occasional, localised research and tests by various authorities over decades. But a comprehensive and countrywide assessment was badly required to make an overall sense of the resources, which is huge but should not be taken for granted.

Why? Because the data analysis from the World Bank-funded project calls for caution.

We must use the groundwater very judiciously and cautiously, looking at the data. Indiscriminate use will only make a disaster imminent.

— DR ANWAR ZAHID Lead researcher and director, WDB

"We must use the groundwater very judiciously and cautiously, looking at the data. Indiscriminate use will only make a disaster imminent," warns Dr Anwar, who is also a leading groundwater expert in the country.

The quality of groundwater is changing slowly from safe to toxic due to unplanned extraction for irrigation, industrialisation, and water supply to big cities. Groundwater levels are falling in two-thirds of the areas in Bangladesh every year.

Home to an estimated 23 million people, Dhaka records a jaw-dropping fall of seven feet (two metres) a year in the water level. If this pattern continues, Dhaka will have to embrace someday the fate of Cape Town or Johannesburg, which provides a scanty water supply to city-dwellers from rainfall storage.

Outside the capital, hand-pumped tubewells that were so commonly used to extract drinking water only a decade back now cannot access freshwater any more down to 165 feet. It is now a thing of the past, as arsenic pollutes the shallow water, with manganese and iodine the new concerns. Money is now on whirring deep tube wells for fetching fresh water from 1,000 feet below.

However, in the 19 coastal districts, salinity made the 1,000-feet depth off-limit for freshwater. The outlook of the drinking water is grimmer even in the middle coastal districts like Pirojpur and Gopalganj although it is not for saline intrusion. Thanks to a unique geological condition, a vast pool of saline water got trapped when the delta was built during ancient times. The one-third area in Bangladesh where the groundwater level is not falling includes the salinity-hit coastal districts.

The withdrawal-recharge (through rainfall or waterbodies) ratio of groundwater is not that encouraging and consistent in all regions of Bangladesh. The rice-producing north is precariously placed.

On the other hand, the western region generally experiences less rainfall than the eastern and it reflects on the outcome. Groundwater depletion is taking place in the west, but not in the east.

Apart from the rice-producing north, the natural recharging of groundwater reservoirs is also not working well in the greater Dhaka region, big cities, and industrial areas.

The WDB project pieces together all the information -- the water level, salinity, toxicity, water-stressed area, acquirers to recharge or leave out, and alternative water source -- in one frame for the sustainability of safe water.

Under the project, WDB upgraded its 905 observatory wells so that water level, temperature, and salinity could be measured automatically, with the data being stored in a central server.

Dr Anwar and his team collected samples from the underground water reservoirs of nature, geologically known as aquifers, at different depths, ranging from 165 feet to 1,100 feet.

After taking 1,802 samples evenly during dry and wet seasons from 901 wells across the country, the specimens were put through 27 tests to determine the applied and chemical quality of water. Over 300 specimens were re-examined at the labs of Dhaka University, Auburn University in the US, and Technical University of Darmstadt in Germany to make the analysis near-perfect.

The team then went on to map the groundwater landscape, putting data meticulously across the region. Upon the painstaking and complex work over years, the manual is finally ready for use.

"The project is to end next year," said Dr Anwar. "But we must continue it, as historic data is very important to set strategy for planned use and recharge of groundwater."