I have just started the book. I has been waiting for me on the shelf for more than 10 years. I tried many times but just couldn't get over the first 20 pages due to so many novel terms and inherent complexity. After watching the movie I finally visualise it and read on. But there is one thing I can't seem to understand and perhaps you can help me: why don't Atreides just trade water to Fremen? Wouldn't it be easier and more effective to get them dependent to their water supply just as the Empire is dependent on Spice?