I already often have heard the point that somebody tries to economize his water use, because (s)he wants to show solidarity with the 880 million people in the world who don’t have access to clean water.
Although saving anything, i.e. also water, is in itself a noble thing, the argument mentioned above shows a false understanding of solidarity. Solidarity has sense when it helps the people/case concerned in any way. Thus, protesting for the international community to help the poor, e.g., has sense – it creates publicity for the problem. But economizing water use (or, for instance, eating up) has no plausible effects on people in Africa or Middle East, where problems with clean water availability are the greatest. We have our own hydrological cycle, and they have their own. Neither drinkable water, nor food can be reasonable transported from Europe to people who really need it (though partly for different reasons). Therefore, if you say you use less water to show solidarity with Africans, it’s nonsense.
Don’t understand me wrong: my case isn’t that you should use water or food without any containment. You shouldn’t. But the reasons why lie elsewhere, not in Africa.