My anime idea

Firstly, I would want my anime to be more to the mature/older audience. With this said, here is my idea:

It is in the apocalyptic future, and water is very short. There are some cities that have plenty of water, which is fresh; however, this is only for the powerful and the rich. So the weak and poor people get thrown out of these cities, and have to fend for themselves in the ‘outside’ world. Which is very desert like, and most things around them is die, and most of it is and empty. The only thing which remains is mostly ruins of old