The dead were among 200 spectators who climbed onto the concrete tank to watch a wrestling match.
The accident happened at a village fair in Kama, Rajasthan state.
The victims fell into the tank, which had very little water in it, and were crushed by falling concrete, said a top local official, R Venkateshwaran.
The injured were taken to a local hospital.
The fair was called off for the day, one report said.
Village fairs are very popular in rural India, with local people flocking to watch mud wrestling, cockfights and drama performances.