A crash course in changing the world.
I imagine the world water day to be similar to the earth day:
For one hour every person in the developed (!) world should stop using any sort of water in any thinkable way (drinking, showering, handwashing...). As there are thousands of activities where people are using water without even realizing it, this event would create an enormous awareness for how we are using water and how much of it. There should be huge information campaigns accompanying the event creating even more awareness. But the event would not just create awareness:
Statistically every German uses 127 liters of water per day, which is approx. 5,3 liters per hour. One hour of complete water-abstinence would mean to safe the unbelievable amount of 433.170.542 liters of water solely in Germany. Imagine how much it would be if every person in the 10 most developed countries in the world would follow this call for action! It would be approx. 470.000.000 people and 2.900.000.000 saved liters of water!
Of course this calculation is unrealistic as there is a high percentage of indirect water use that people cant influence themselves. Probably a good-guess for the amount of water that people can actively save would be around 30% of the overall statistic water use per day. Applying this calculation to the 10 most developed countries would still mean that not-using water for just 1 hour would mean to save 870.000.000 liters of water!