I gave up sugar once and the changes were massive (though I only drank water as well).
First, my skin started clearing up. The red tinge, small blotches and roughness went away and even though I was in my late-20s, people thought I was younger. My hair went from being straw-like to soft and silky (girls would like that one). The weirdest change was at night when I was laying in bed, all I heard was complete silence. You don't really notice the sound of your blood circulating or the very faint sound of your heartbeat. I found it very easy to sleep, all my aches and pains went away. My bones stopped clicking etc.
I had a greater sense of calm and tranquility and my thinking became clearer. I found that I was reading more and had more patience. I began to organise my life better.
After a while, I became less spontaneous and creative. I couldn't banter with friends like I did before and I became more aware of my surroundings. Small, trivial things began annoying me, I didn't laugh as much, I got into arguments with people easily. Then my legs began aching constantly to the point I couldn't sleep. I put up with this for another two weeks before going back to sugar.