With the water table dropping as the city grows, water conservation and harvesting will be key
DHAKA, Bangladesh (AlertNet) – Bangladesh’s water experts are forecasting a water crisis in the country’s capital, due to its rapidly rising population and overdependence on underground water which is being depleted at an alarming rate.
According to the World Bank, Dhaka is fast becoming one of the world’s largest cities, with its population of nearly 14 million expected to rise to 22-25 million by 2020.
“Every day new buildings are rising up and people from the countryside are pouring (in) here, but no new water sources are created,” said Hasin Jahan, programme director of WaterAid Bangladesh, a development organisation.
According to Jahan, the area of Dhaka city has doubled in size since the 1990s and the population has increased by 1.5 times. Water for drinking is only part of the issue, she said. Large quantities are also consumed by everything from flushing lavatories to gardening, and washing cars to construction work.
At present Dhaka is dependent on underground sources for 87 percent of the 2.2 billion litres of water consumed every day. The balance is collected from surface sources.
The Dhaka Water Supply and Sewerage Authority (WASA) extracts groundwater using 620 deep tube wells. In addition, more than 2,200 private wells also draw water to serve high-rise buildings and various institutions.
FALLING WATER LEVELS
But the overdependence on groundwater is causing the water table to fall by about one meter (three feet) per year in the metropolitan area. According to Eftekharul Alam of the Bangladesh Agricultural Development Corporation, by 2011 Dhaka’s groundwater level had dropped to 52 metres (169 feet) below mean sea level, compared with 46 metres (150 feet) in 2004.
“The excessive extraction of water by the Dhaka WASA is causing the water level (to) drop,” he said.
Alam, an agricultural, water and environmental engineer, said that the underground water supply used to be recharged with water from nearby Gazipur and Mymensingh districts. But this is no longer happening as the water level in those districts has itself dropped.
Worse, Alam anticipates a serious water crisis in the capital because the aquifers are now being recharged with seawater, he said.
“Saline water is intruding to fill up the space, posing a threat to getting fresh drinking water in the future,” he said.
The only effective way to recharge the aquifers, he said, is by injecting rainwater and river water – but that would first have to be treated to ensure the aquifers don’t become polluted.
Alam said the Dhaka WASA emits 1,000 tonnes of untreated human waste into the rivers adjacent to the city every day, which means river water is unfit for human consumption.
PLENTY OF RAIN
However, WaterAid’s Jahan said the average rainfall in Dhaka is more than 2,100 millimetres per year, and that a significant amount of this could be used to meet water demand and recharge aquifers if it were captured.
The organisation has constructed four rainwater harvesting systems in Dhaka. The water gathered is used partly for flushing lavatories and partly for groundwater recharging.
The Institute of Water Modelling (IWM), a government organisation, estimates that if 60 percent of rainfall falling on the existing concrete rooftops in Dhaka were harvested, it would provide nearly 200 million litres of water to residents each day.
Managing director of Dhaka WASA Taqsem A. Khan said that steps are being taken to gradually reduce the city’s dependence on groundwater because of the declining water table. According to Khan, it is difficult for groundwater to recharge adequately in the city because of the increasing lack of open space for it to collect.
“Artificial recharge of the underground aquifers through injecting harvested rainwater is the only solution,” Khan said.
WASA is constructing four surface water treatment plants in Dhaka at a cost of $1.8 billion, with the aim of supplying 70 percent of the city’s water demand from surface sources.
Water for the plants will be drawn from less polluted rivers 60 km (38 miles) from the city. The plants are expected to produce about 1.6 billion litres of clean water per day.
Conservation of water will be equally important to dealing with growing demand, Khan said.
He thinks that the city’s daily demand for water will not exceed 2.3 billion litres in 2021 if individual consumption can be cut down to 80 litres per day.
“Presently Dhaka (residents) consume 120 litres of water per person per day, which is not usual for people of a less-developed country,” he said.
He said most water waste was the result of a general lack of awareness of the need for water conservation and irresponsible water use by middle-income and rich residents.
Syful Islam is a journalist with The Financial Express newspaper in Bangladesh. He can be reached here.
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