The deceased, identified as Jaipal Singh (56), had gone missing on July 13, he said.
Today, a foul smell was emanating from the water tank, following which the residents of the house alerted police, he said.
No injury marks were visible on the body, the official said.
In her statement to police, a domestic help, identified as Kamla, said Singh was on duty when she had come for work at 8 am on July 13.
At about 9.30 am when she had to leave, Kamla found that the main gate of the building was locked from inside and Jaipal had disappeared from the spot, according to her statement.
The owners of the house were abroad at the time of the incident.