Despite being the world's largest delta having an estimated 1,210 billion cubic metres of fresh water, the country depends mostly on groundwater for drinking and dry season irrigation in the absence of a sustainable water use plan.
About 98 percent of drinking water and 80 percent of dry season irrigation water comes from the 21 billion cubic metres of groundwater reserve.
This was stated by Anwar Zahid, deputy director of Bangladesh Water Development Board (BWDB), at a press conference yesterday on the eve of the World Water Day.
He warned against the dangers of increasing dependence on groundwater, and unplanned use of water resources of the country, crisscrossed by about 700 rivers and tributaries.
Pollution of surface water in cities and industrial zones is the main cause of dependence on groundwater. Even fields located near rivers are often irrigated using groundwater rather than river water, Anwar said.
"It is easier to set up a tube well rather than installing pipes [from rivers to the fields]. The pipes have to be removed during rainy seasons when the fields get inundated by flood water."
The over extraction of groundwater would lower its level and increase salinity in coastal areas, he said. When the groundwater level goes below the sea level, saline water flows inwards during tidal surge in rivers.
"In Dhaka the groundwater level is going down by 1 to 3 metre every year," Anwar said.
"In the 70s, a depth of 350-450 feet was enough for Wasa [Water Supply and Sewage Authority] to install tube wells. But the required depth is now 500-1,000 feet now,” he said, adding the installation cost too has gone up.
Besides, the properties of the aquifer, the soil that holds the water, are being damaged. The soil might become compact and its capacity to hold water in future might be lost, he warned.
Many recent studies also show that fluctuation in groundwater level during dry and wet seasons is a factor in arsenic contamination of water.
"Now we have an act based on which laws can be made to control the use of groundwater for irrigation. For example license or permission to install irrigation pump must be obtained from government and deviations should be made punishable," Anwar Zahid said.
He suggested implementing projects to preserve surface water, such as the Ganges barrage in Rajbari, and rain water harvesting system.
The Ganges barrage, when implemented, will retain water of the trans-boundary river, known as the Padma in Bangladesh, during the rainy season for use over the rest of the year.
Although the idea of the barrage was proposed in the early 60s, the project is yet to be completed.
Besides, farmers should be made aware of misuse of water.
"About 3,500 litres of water is needed to produce one kg of rice, but farmers often use twice as much," he said.
The press conference was organised by the Department of Public Health Engineering, Policy Support Unit, United Nations Information Centre, Unicef, World Bank, Oxfam, Bangladesh Wash Alliance and NGO Forum for Public Health at Jatiya Press Club.