Water was just listed as one of the items we need to survive as opposed to something we want, we pretty much already have it in abundance in the first world.

I'll admit I used to have the same view on this, where is the incentive? Why would someone do something without this immediate reward system? But it is this problem which I think would create the best (or at least most interesting) results. Without immediate reward the farmer will stop farming, why should he keep working for others? Agriculture then becomes a problem for society to solve in the most efficient way possible instead of a status quo job for a few individuals. In going back to the original point of this page, imagine the hacker community's response to that, a real, important problem to solve.

So to answer your last question, with the lack of currency/money there is no difference between them, the only form of advantage to be gained is in your social standing (interesting implications on leadership here), using your skills to help others and solve societies problems is your only way to gain any advantage over others.