What were the deep holes that surrounded the city of Dholavira used for?

The deep holes were often used for storing WATER

Explanation:

The deep holes which surrounded the city was majorly and often used to either store WATER during raining reason or to store diverted WATER or water that flow from nearby streams reason been that the city of Dholavira is a desert and the second reason is that many years may pass without the city of Dholavira experiencing rainfall which was the major reason they often make use of the deep holes that surrounded the city to store WATER.