Water Wastage — My opposite apartment is wasting water by overfilling the tank

The building next to mine wastes a lot of water. Over the past few weeks i have observed that the overhead tank starts to overflow around 3-4am and continues to overflow till 8-9am till someone turns off the pump. Again, during the day the tank overflows at least a couple of times and continues till someone notices. There is no garden or anything and this huge amount of water just goes to waste. I learn from people that they had a leakage problem in the top floors because of this and instead of regulating the water overflow, they just waterproofed the terrace