Installing separate tank for each house in an apartment

We were facing accute water shortage and we do not have an metro water connection. Out of the 5 houses, although all the other four of us are willing to get a connection, one owner is not cooperative. Also there has been lots of troubles created by him and there is no common maintenance also taking place in the apartment. All the 4 of us decided to erect separate tanks (500 ltr) and separate motors giving electricity for motors also from their houses. As the sump tank is not used at all, we decided to fill it by tanker and use. Also informed the other owner if he is installing the tank he can also use the water in the sump tank. But he is allowing us to proceed though. Is it illegal wat we are doing. All the four of us in the 5 houses have agreed to it. Is it ok to proceed if majority of us are willing to do it. Kindly advice