A Film about Water
The story of Chinatown, as originally seen in the mind of Robert Towne, was inspired by the California Water Wars. These were a series of political conflicts that took place between the city of LA and various farms and ranchers in the nearby Owens Valley. As the city of LA was expanding in the 19th century, it was becoming too big to cope with its existing water supply.
It needed more water, and the mayor at the time thought he could make an aqueduct to take water from the Owens Valley. Farmers and ranchers in the area resisted, but the mayor eventually got his way, with a lot of political tricks, lies, and deceit allegedly involved in the story. For Robert Towne, it was a great foundation for a film.