Tap water isn't fit to use anytime let alone a fast. I drink super distilled water which is compressed to create microclusters and a perfect molecular structure. This is the water I have researched for myself and after trying so many others, I feel best when I drink this water, For cooking I use alkaline, Ionized Water (filtered as well). I haven't drank tap water in years and years. When I even come close enough to smell it I wonder how anyone can drink that toxic sludge.