Arsenic-free groundwater has been found in Barguna and Patuakhali districts through the use of isotopic techniques.
It could be a viable additional source of drinking water for a region made up of over two million people.
With the support from the International Atomic Energy Agency (IAEA), Bangladesh Atomic Energy Commission (BAEC) conducted the study from 2016 to 2019.
The study characterised groundwater recharge–the hydrologic process involving the movement of surface water to subsurface groundwater–in arsenic-impacted areas, and salinisation in the coastal aquifers of the country.
"The government of Bangladesh has given top priority to domestic water supply, including arsenic mitigation and sustainable groundwater management," said Nasir Ahmed, isotope hydrologist at the (BAEC)–the organisation that led the study.
"The isotopic data collected during the study will be used to further guide the optimisation of sustainable groundwater management policies," he added.
The isotope data from the study revealed the existence of long-term high quality drinking water in the deeper 300-metre aquifers in Barguna and Patuakhali districts.
"Isotopic techniques are a valuable tool for evaluating arsenic mobility in aquifers and the groundwater recharge mechanism," said Umaya Doss Saravana Kumar, Isotope Hydrologist at the IAEA.
"Sustainable groundwater resource management requires an understanding of recharge processes, their source and origin, as well as the geochemical evolution. Isotope techniques help in all these areas," he added.
According to the World Health Organization (WHO), surface waters are saline in most of Bangladesh's coastal rivers, and groundwater is the main source of safe drinking water.
However, shallow groundwater in the country has high levels of arsenic; a toxic metalloid present in the local geology in contact with groundwater.
Contaminated water used for drinking, food preparation and irrigation of food crops poses the greatest threat to public health from arsenic. Long-term exposure to arsenic from drinking water and food can cause cancer and skin lesions.
The study said, the availability of groundwater to cover human needs depends on its quantity, quality and rate of replenishment.
Information on the source and age of groundwater is required to properly assess the sustainability of the resource; particularly in view of existing or planned withdrawal activities.
The deeper groundwater found in the Barguna and Patuakhali aquifers showed no sea water contribution or arsenic.
And the age of the groundwater appears to be 9,800 to 31,700 years BP, indicating the presence of old recharged water.
This indicates that the water flow is slow; though the aquifer may take a long time to replenish it is also less affected by pollution and changing climatic conditions.