All the reservoirs that cater to Chennai and its suburbs were empty before Diwali. Consistent rains started on November 8, lasting a week, and were followed by another spell on November 23, which was not forecast. By the end of November, the level in the reservoir had reached its limit. Water in the Chembarambakkam reservoir — one of the city’s main water sources — stood at 22 ft at this time, against its capacity of 24 ft. Official data shows outflow from the reservoir, into the Adyar river, as 900 cusec then.

It started raining again on December 1, and continued into December 2. By December 1 afternoon, the water in Chembarambakkam had swollen to 3,396 million cubic feet