"According to data collected from NASA and the World Health Organization, 4 billion people will face water shortages by 2050. Already in China, water levels in the Yellow River -- a source that supplies more than 150 million people -- are down 33 percent from the average. In China's cities, wastewater pollution and inadequate treatment facilities have contaminated the water consumed by more than half the population. Of its 669 major cities, 440 face moderate to severe water shortages. "
On the local city buses there are advertisements saying a can of tuna of water per week is enough for your lawn. I'm not sure why they chose a tuna can, but, for your information, that's 2.5cm of precipitation. Even more impressive I found an organization which promotes peeing on your lawn instead of watering it. You save water twice, since you don't need to flush or water your lawn:
"So take a piss in the garden, and while you are doing that, look out at your garden and think about how lucky you are, to be surrounded with all of what nature provides. Surely, there is something we can all do to help water conservation."
So far almost 4000L have been saved. I know I'll do my part...