Well my mothers day cake was a huge success, and it was my first time working with fondant and gumpaste!

Now I have my sons BDay cake I am working on. I am moulding all his favorite characters out of fondant to create a "Bas Relief" to go around the bottom. I have one question..... can I stick the fondant pieces together using water?

Yes, you can dab on a little water - many people do that. I like to use a little piping gel because it is a little stickier. If you are doing really large pieces, you can also use thick royal icing as a sort of "glue" but from the sound of your project, it doesn't seem like you need something that extreme.

Water works, I made a 'glue' using a blob of fondant mashed into hot water to get a gooey paste, it has better sticking properties that just the water
HTH!