I believe you are water fasting. I have done a lot of Master-Cleanse
(mono juice fast) and juice fasting (consuming 3-6 cups daily of freshly made fruit/veg juices daily). Juices have allowed me to continue my daily exercise routine every fasting day, barring crises, and keep my energy level high throughout. I have done short water fasts, usually during a juice fast, to deepen the cleanse or to alleviate nausea or another detox reaction.
I drink herb teas to relieve the monotony of fasting, and have also sipped tea during lovely dinners out with friends... teas have also helped relieve detox symptoms like nausea and kidney pain. My big faves are chamomile, cinnamon, ginger, mint and rose hip, but I cannot imagine why any herb tea wouldn't compliment a fast in moderation. Stevia makes a good sweetener that doesn't affect your cleanse.
Have a good one!