The government has taken preparations to make rainwater harvesting compulsory for every building in the capital, according to the draft of the revised Bangladesh National Building Code (BNBC).
The revised BNBC, currently waiting for vetting at the Ministry of Housing and Public Works, says every building in the capital having at least a 300 square metre rooftop must have a rainwater conservation system and also a well to recharge underground aquifers. The entire process, as recommended, will incorporate collecting and storing rainwater for the future use, while some amount of water will also be instilled into the underground aquifers through specially designed recharge wells.
Earlier in a circular on May 6 last, the housing ministry said buildings of 500sqm or above in Tejgaon Industrial Area of the capital must have rainwater harvesting arrangements. Experts observed the government’s move as such will help reduce groundwater depletion.
They hailed this move by saying that many countries across the world have been harvesting rainwater and recharging the aquifers through similar arrangements. They also said this can be a sustainable solution to the growing water crisis in the capital.
According to the revised BNBC, rainwater harvesting system must be installed by taking prior authorisation from the Rajuk (Rajdhani Unnayan Kartripakkha) so that only fresh rainwater is recharged into the aquifers.
The code also said the whole process should have involvement of qualified plumbers to take care of the system.
“An application for a permit for rainwater harvesting and drainage work shall be submitted… by a licensed plumber and the [building] owner or by their appointed person or agent…” reads the code.
Taqsem A Khan, managing director of Water Supply and Sewerage Authority (Wasa), said it might need around Tk 5 lakh to install each groundwater recharge system.
“If all government buildings follow the [revised] building code, 20 to 30 percent areas of the city will be covered,” he said.
Layer of the groundwater in the capital has dropped by a large margin over the recent years, as Wasa extracts a huge quantity of groundwater for an ever-increasing population of the capital through a large number of deep tube wells.
A total of 805 deep tube wells across the capital and four water plants, located at Sayedabad and Chandnighat in Dhaka, and at Godnail and Sonakanda in Narayanganj, supply around 80 per cent of the total need of water of the capital, according to Wasa.
“Over 2,000 authorised private deep tube wells across the city are also extracting groundwater. And there are around 2,000 illegal ones too,” said a Wasa official seeking anonymity.
These Wasa deep tube wells, and also the illegal ones, that extract crores of litres of water are depleting the groundwater layer at an alarming rate, said he.
According to a Bangladesh Water Development Board report, the average rate of annual groundwater decline in different parts of the city was 0.17 metre to 0.6 metre from 1970 to 1980; 0.15 metre to 0.69 metre from 1980 to 1990; 0.56 metre to 2.26 metre from 1990 to 2000 and 1.24 metres to 3 metres since 2000.
Anwar Zahid, director of groundwater hydrology at BWDB, said the reasons behind the declining groundwater are excessive extraction, filling up of low lands, canals, water bodies and unplanned urbanisation.
A Wasa official said excessive use of groundwater is quite interesting in a country which is cobwebbed by so many rivers, including at least five of it flowing right through the heart of the capital. But a mindless dumping of human and industrial waste has polluted the water of the Buriganga river has become toxic beyond the use for domestic purpose.
Dhaka Wasa in 2009 began a pilot project, titled “Artificial Recharge from Rainwater” at 10 places of the city. The places are Lalmatia, Mirpur, Uttara, Segunbagicha, Banani, Gulshan, Khilgaon, Motijheel, Mohammadpur and Gandaria said a Wasa official.
Under the project, rainwater is being harvested, filtered and sent to aquifers through wells on a limited scale, the official said. The Institute of Water Modelling (IWM) is carrying out a field analysis on groundwater recharging of those sites, the report of which is yet to be submitted.