The workers were engaged by a contractor to undertake repairs on the 100-feet high water tank situated in a housing colony.
Two died on the spot while the others succumbed to injuries on way to hospital, police said.
Electricity Minister T Thiagarajan accompanied by legislators M Vaithianathan and Ashok Anand visited the spot.
Thiagarajan later told reporters that an inquiry would be held into the incident.
Police have registered a case.
