What can I drink while fasting?
Water, black coffee, plain tea and unsweetened herbal infusions are all fine. Anything with sugar, milk or meaningful protein is not.
The rule underneath all of this is simple: if it carries enough energy or protein for your body to treat as food, it ends the fast. Almost everything else is fine.
Safe in practice: still or sparkling water, black coffee, black and green tea, and herbal infusions with nothing added. Plain electrolytes without sugar are also fine, and worth considering on longer fasts.
Not safe, though people often assume otherwise: anything with milk or a milk alternative, fruit juice of any kind, sweetened drinks including diet versions that contain sugar alcohols in quantity, bone broth, and any coffee with butter or oil in it.
Hydration deserves more attention during a fast than outside one, because a sizeable share of most people’s daily fluid normally arrives with food. If you are eating in a shorter window, you have to drink more deliberately to make up for it.
General information, not medical advice. Intermittent fasting is not right for everyone. Talk to a clinician before starting if you are pregnant or breastfeeding, have or have had an eating disorder, have diabetes, or take prescription medication.