This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
Due to the bad taste in the mouth while one is fasting, the water is likely to appear to taste badly. At other times patients complain of the water being too sweet. They frequently request permission to add salt or lemon juice or other substances to the water to flavor it. The evils of salt using were discussed in the chapter devoted to "Objections to the Fast." The use of lemon juice means that the patient is taking food, and although he takes but minute quantities of the juice, it is enough to interfere with the fasting process and is often enough to cause a return of hunger and thus makes the fast much more difficult, or compels its premature breaking. It is never wise to add anything to the water. For the bad taste in the mouth one needs only cleanliness. The teeth, tongue and mouth must be cleansed. The tongue should not be brushed before it has been examined each day.
In the summer time patients are likely to demand ice-water to drink. Drinking very cold water is not a good practice under any circumstance; it is especially harmful during a fast. Indeed, giving very cold water to fasters seems to almost stop their progress. There can be no objection to giving them cool water to drink.