The UNICEF Tap Project sponsors projects to provide clean drinking water to the hundreds of millions of people who don't have it. This year, they've created an online challenge: for every minute you spend away from the phone, Giorgio Armani will pony up for a day's clean water. (Just go to the Web site on your smartphone and it'll go to the challenge.)

This is a serious global problem, as the Tap Project's Web site explains:

768 million people do not have access to safe, clean drinking water, and 2.5 billion people live without proper sanitation. When water is unsafe and sanitation non-existent, water can kill.

Across the globe, every day, 1,600 children die from diseases directly linked to unsafe water or a lack of basic sanitation facilities.

What I love about this is that most social or mobile challenges tie activity– liking your cause on Facebook, retweeting, etc.– to such rewards. In this case, though, you contribute literally by doing nothing– but a good sort of nothing.

It works by measuring movement: you have to put your phone down, it detects that it's not moving, and then the timer starts. So it's literally "don't touch," not just "jiggle it nervously but don't actually DO anything with it."

Once you start, your screen shows a blue screen (watery blue, not screen of death blue) with a little timer. After a couple minutes, I expected to see some change– water glasses appearing, or something that indicated how much social good my phone had done by doing nothing– but after several minutes it stays serenely un-animated. At the end it tells you how many days you've donated.

I suspect this is eminently game-able, in that I could turn it on, go to a meeting or dinner or sleep, and just let it run. Which is probably part of the point.