Try keeping your mouth shut, breathe through your nose, avoid speaking or exercising if you cannot do it aerobically (nosebreathing).
It sounds like you will need to take breaks and rehydrate if aiming for 20 days of fasting, but I do not think there is any use doing it for like a day or even less, better to rehydrate properly for at least a few days and then go again.
If you drink water your body will not feel the need to create it, which is the whole point of the fasting. So if you do drink I think it would set you back a couple of days anyhow