Why do some cultures invest more for the long term, whereas others emphasize living in the moment? We took advantage of a natural experiment in Iran to test the theory that long-term water scarcity is an important cause of differences in long-term orientation and indulgence. We found that Iranians in a water-scarce province reported more long-term orientation and less indulgence than did Iranians in a nearby water-rich province (Study 1, N = 331). In a field study, Iranians in the water-scarce province sent more résumés for a long-term job ad we posted, whereas Iranians in the water-rich province sent more résumés for a short-term, flexible job (Study 2, N = 182). College students in Iran primed to think about increasing water scarcity in the environment endorsed long-term orientation more and indulgence less (Study 3, N = 211). Across 82 countries, long-run water scarcity predicted long-term orientation (Study 4). In sum, cultures in water-scarce environments value thinking for the long term more and indulgence less.