Fasting is self-denial. God views it as an act of humility. There is a study in the Sermon on the Mount that you may be interested in. It is a study on fasting.
Yes, you can drink water during a biblical fast. Fasts were usually denial of just food. However, the book of Esther does describe one unusual fast that included going without food and water.
The normal fast only excludes food.
Prayer and spiritual fasting always occur together. There are no rules about how often to pray, it is completely up to you. God only requires that our hearts are sincere and that the fast is between you and God (Isaiah 58:3-7).
How do you start? If it were me, I would start the morning with some water and continue drinking water throughout the day. I would also start with prayer and the reading of His Word. The rest of my day would be given to prayer and submitting myself to Him.
Conclusion:
When we fast, Jesus told us to fast in secret. Fasting should be between us and God. If you are humble and seriously seeking Him, He will honor your fast.
when fasting can you drink water or juice?