I hear different things from different sources considering what you are and aren't allowed to consume during intermittent fasting.
One source [Dr. Ronda Patrick] states that anything other than water violates a fast. However, she speaks of 'time-restricted eating' rather than 'intermittent fasting'. By the sound of what she says it's like she's talking about a completely different thing because other sources allow for any kind of drink that has 0 calories [such as coffee, water, tea... even no-calorie sweeteners and drinks like Diet Dr. Pepper are allowed].
Some sources even allow for caloric consumption under 20-30 calories [like almond milk with coffee].