Oasis of the Elementals

From publisher blurb:

It's the Arabian Nights meets A Fistful of Dollars when your party enters a desert oasis on the verge of war between two gangs who want to control its main attraction — a spring with magical waters. However, nobody is aware that powerful water elementals lurk at the bottom of the spring, and they aren't happy about humans taking advantage of their turf. Throw in a djinni and an efreeti who are best of frenemies, and it's our wildest Places by the Way yet!

Oasis of the Elementals is published under the Open Game License. It does not specify a particular campaign setting, and it allows you to integrate it into your own campaign world by filling in various details.