Around 85 percent of houses in the capital's Gulshan, Baridhara, Niketan and Banani areas have their sewerage lines connected to nearby lakes and canals, polluting the waterbodies, revealed an assessment.

Sewerage lines of 3,265 out of 3,830 houses are connected to canals, lakes or Dhaka North City Corporation's (DNCC's) surface drains, which are only meant for collecting water from rainfall and kitchens for later use.

These homes should have had a separate sewerage connection to Dhaka Water Supply and Sewerage Authority's (Wasa's) network for proper sanitation, it said.

Unicef and EQMS Consulting Limited conducted the assessment in the four neighbourhoods in October and November last year.

Referring to the assessment, DNCC Mayor Atiqul Islam, during a drive yesterday, said the city corporation will not allow anyone to dump waste into lakes and surface drains.

Many houses are illegally connected to surface drains, which makes it difficult for the corporation to use the collected water for fish farming. Furthermore, this situation leads to  mosquitoes proliferating, he said while talking to reporters during the drive on Road-112 in Gulshan-2.

During the drive, the sewerage lines of two houses were sealed up for dumping waste into lakes and surface drains.

"The waste of the two houses is supposed to be dumped through a separate line of Wasa," Atiqul said, adding that the owners had been informed about the drive a year ago, but they did not take any measures.

"It is advisable for residents to check if their water line is properly connected. Residents pay their sewerage bill to Wasa every month, but their house is connected to DNCC's drains," the mayor said.

The drive will continue in the areas, he added.

Besides, the assessment found that out of 1,166 houses in Banani, 1,023 are connected to lakes and surface drains. In Baridhara, 342 of 550 houses have no sewerage lines connected to Wasa.

In the Gulshan West area, 791 of 864 houses have illegal connections. In the Gulshan East area, there are no separate sewerage lines for 736 of 818 houses. In Niketan, 373 of 432 houses are also dumping waste ignoring the rules.

The survey found that in all these areas, only around 41 houses have separate sewerage lines, while 524 (13.6 percent) homes have partially complied with the rules.

Former Buet professor Mujibur Rahman, who led the assessment, said although Wasa's sewerage network exists in Gulshan and Banani, it is not present in Niketan and Baridhara, which rely on septic tanks.

"One percent of houses in the four areas have a safe sanitation system. Sewage flowing into local lakes and canals leads to the water getting polluted," he said.

Aminur Rahman, a resident of Gulshan-2, said, "I pay my bill every month for the sewerage line. I wasn't sure if the line was connected to Wasa or not."

Contacted, Dhaka Wasa's superintending engineer Touhidul Islam Murad refused to comment on this matter.