The incident occurred last night when Moti Yadav, a tea vendor, was walking on the road when he suddenly slipped and fell inside the under-construction pit, Madhapur police station sub-inspector Chandra Shekar said.
The pit was being dug for laying drainage pipes.
He said there were some electric wires in the pit that were cut and Yadav could also have suffered shock during the mishap.
"Due to heavy rains the area had got covered. Some passersby who noticed him falling into the pit immediately rushed to his rescue, but he drowned in the under construction sewerage," Madhapur Police Station Inspector R Kalinga Rao said.
A case was registered under section 304A (causing death by negligence) of IPC against the contractor who had undertaken the sewer line construction work, Chandra Shekar said.
Further probe is on.