The principal, Rekha Kakkar, who was suspended following a preliminary enquiry by SDMC, was arrested this noon after the police received a report from the civic body and its findings corroborated statements recorded earlier, a senior official said.
The principal of the SDMC school was later released on bail, the official added.
DCP (south-west) RA Sanjeev confirmed that the principal was arrested today but did not share any other details.
SDMC authorities had ordered a probe into the incident by the civic body's Additional Commissioner (education) Rajesh Pathak.
A case under Section 304A (causing death by negligence) was registered in connection with the incident.
The incident took place on January 27 when the nursery student, Ankit Kumar, slipped into and drowned in the tank on the school premises.