Here is a brief, clear answer:

Why Indian major cities face groundwater depletion (Briefly)

1. Over-extraction:
   Too many borewells pumping more water than nature can recharge.
2. Concrete everywhere:
   Cities are covered with roads, buildings, tiles → rainwater cannot enter the ground.
3. Loss of lakes, ponds, wetlands:
   Natural recharge areas are encroached or polluted, so aquifers don’t refill.
4. Population growth:
   Water demand increases faster than supply infrastructure.
5. Irregular rainfall due to climate change:
   Short, intense rain causes runoff instead of groundwater recharge.
6. Pollution of groundwater:
   Sewage and industrial waste contaminate aquifers, reducing usable water.
7. Deep construction & metro tunneling (local impact):
   Excavations disturb shallow aquifers and change groundwater flow.

If you want, I can also give city-wise short reasons (Bengaluru, Delhi, Chennai, Hyderabad, Mumbai).