I agree that overpopulation is a problem, but it does not excuse anyone from not wasting water. There are parts of the world where catching rainwater from your own roof is illegal, but nicely watered lawns in front of office buildings aren't. Nor are low-flow aerating faucets or ultralow-flush toilets mandatory.
Africa is often used to show contrasts because many parts of it are among the worst places in the world: Not only are there more people than can be sustained, but even when water is found, more and more often it is poisoned by foreign mining corporations (which don't care whether they tear up desert or valuable farmland to get what they want).
And the rest of world, instead of trying to help by educating about the effects of overpopulation, keeps sending medical and food missions that keep more people alive, healthy, and fit for reproduction. The only "help" with population control that gets sent to Africa are machine guns and land mines, and that is sent to all sides of each conflict, with quite a profit.
Sorry for going off topic.