Unequal head level of water distribution from overhead tank in my apartment

Apartment consisting of 6 Flats sharing common concrete water tank

Background: Our Flat is based in Tambaram, Chennai. There are 6 flats in an apartment. We share common overhead concrete tank. During summer we face acute water shortage problem. Even after starting the pump and it is running for half an hour, we won't get a drop of water. We are living in ground floor. Since there is lot of suffering especially on Sunday where all the members of family will be present and water needs will be more, I went inside the overhead tank to check what is wrong. To my shock, out of 6, two apartments water inlet line is at lower level than others (pictures attached). Of the rest four apartments, two vacated their house, another apartment connected their water line to the common drain. Things done: Case-I: There is a tap which is at ground floor. so whenever, pump is running, my mother used to take water from it. The neighbours (culprit ) starting a huge fight that they are not receiving the water overhead and we practice the same method they will turn of our ball valve. Case-2: We asked another apartment owner to remove their connection from drain line, to which she refused and said you can also take a line from them. When we attempted doing it, the same culprit neighbour threatened us that he will inform police. We refrained from our action thinking that it is not legal. Case-3: We attempted to make all lines equal in level with the existing two apartments, to which there is no support or the another owner is telling us to take the lead. My family is worried