Why did people not face scarcity of water in Rajasthan in ancient times? 

Looking at the case of Rajasthan which receives the least amount of rainfall. It only rains for a few days in Rajasthan. Though people never faced scarcity of water. This is because there were arrangements for collecting and storing water such as Paulis, bawdies, and stepwell. Everyone had access to them. 

Rajasthan does not receive heavy rainfall. So it is an incorrect option. 

Therefore, the correct answer is an option (A).