Why Lord Ganesha idols immersed in water after Ganesh Chathurthi?
Earlier Ganesh idols used to be made of clay. And they would have a coin in the idol. And these idols were to be dissolved in Ponds/Lakes. Now the reason for dissolution is this- in order to retrieve the coins, people would walk in the pond. This would set the clay in pond and this is supposed to be effective rainwater harvesting method. This process ensures that rainwater doesn't drain away from pond.