a site that i would highly reccomend is
http://www.icomm.ca/dragon/ it was all the information you will ever need, and as for laying on their backs, i wouldnt do that, what makes it seem like they are relaxing is that they are devoting their energy to breathing because in that position it is really hard for them to breathe. Water Dragons are a great reptile, though i would reccomend getting a larger dragon, over 10 inches to start out with, because sometimes they can become very stressed when moved into a new inclosure. hope this helps.