While fasting, you can drink water, green tea, black coffee (without any added sweeteners or creamers), and other non-caloric beverages like herbal teas.
it’s best to consult a healthcare professional to determine if it’s suitable for you and to discuss an appropriate frequency and plan. Some people choose to fast regularly, whether daily, weekly, or monthly, while others fast occasionally. The 16/8 method you mentioned is a popular intermittent fasting plan, where you limit your caloric intake to an 8-hour eating window and fast for the remaining 16 hours.