Installing separate water meters for 120 flats in an apartment complex in Coimbatore, Tamil Nadu : Need costs & concerns

I live in Coimbatore in an apartment complex.The association has over the years noticed very high usage of water by the residents.We have however, not installed separate water meters for individual apartments (totally 120 in number). Occupancy is around 80 or so. We have three connection from the Coimbatore Corporation apart from six borewells of which 3 are in use. The estimated consumption of water is  almost 1 lakh litres per day. Raw water is treated before being pumped up to the overhead tanks.

All the sewage and drainage water is treated in the treatment plant before being used for gardening.
Each of the flat has either three or four water inlet pipes from the overhead tank. Therefore there arises the question of where to install the water meters.

Is it possible to do so now and what would be the costs involved in such an exercise? Contact information of a suitable consultant or general guidelines to help in the matter would be welcome.

Geeta Sridhar