Drinking only water for a month?

This is a very healthy option, water is much better for you than any sugar drinks, you will definitely loose weight. However if you're thinking of working out i suggest that you drink gatorade or powerade in order to gain much needed electrolytes. One thing you can also do is add (very) small amounts of salt in your water to ensure you have the correct levels of salt in your system to prevent cramps (na+ ions help teh co-ordination of muscle contraction, a limited supply of this causes erratic contrition of muscles)