I find when I am rolling out pie dough that the dough starts cracking. Is that because the dough is too dry and needs more water?

Yes! Dough that is under-hydrated will be likely to crack during rolling. Take a look at this picture. The dough on the left is a little too dry - it looks visibly dry on the surface and even though it mostly holds together when squished, it also breaks apart a bit. The middle dough is properly hydrated - even though there is variation in color and texture, it holds together smoothly, and will roll out nicely! The dough on the right is over-hydrated and too wet: sticky to the touch and will be hard to roll out!