I used the Cambridge Diet and lost weight quickly, so it does work. The water issue for me was not to count how much water I drank but have a .5ml bottle which I kept refilling and drinking from as the day went. The first few days you will be using the loo often, but it's not a permanent thing.
The only draw back for me and this plan? I could not afford to use it consistently and I put the weight right back on after stopping. It was not immediate but a gradual process.
Good luck and be safe and I hoped I helped you somewhat?