We all know drinking water is good for us -- but drinking ONLY water, can it be good for you? These brave souls found out the hard way.

At the Day Nine mark, the participants were regretting the only water drinking decision and it was very hard to socialize without the temptation of having a happy hour drink. Day 21 was a little better, as they now were over the hump and water didn't seem all that bad. They even did an endurance challenge and found that they lasted longer during the vigorous exercise.

Overall, water is essential to a healthy diet, but everything has a limit. Gotta do things in moderation. So the moral of the 'only water challenge' is, get your 8 glasses a day and be healthy!