-- I cannot specifically find where Shelton talks about not adding anything in the water (extreme case: "adding" all the ingredients of the diet coke/coffee). If you find it in the book, please share. Vitamins seem to me more "benign" things to add, but it is somewhat counter intuitive and probably harmful, since Water Fast is total GIT nutritious abstinence from any outside source..
My impression is that Olivia Cohen did not consume drinks other than water and her vitamins on her water fasts. Her 3 consecutive 40 days fasts, only spaced by 10 days of eating food, more over meat as a first meal, are extremely dangerous example to follow. The body should be allowed to recuperate for quite a while after a long fast. I do not think that even Jesus did 3x 40 days fasts in a row. The faith of Cohen is admirable, but she could have died in the process...