Christian fasting isn't some kind of a "work" that's commanded by Christ or required by Scripture. However, that doesn't mean that fasting isn't recommended as a part of our spiritual growth. The Book of Acts records believers fasting before they made important decisions (Acts 13:4; 14:23). Fasting and prayer are often linked together (Luke 2:37; 5:33). Too often, the focus of fasting is on the lack of food. However, the purpose of fasting is to take our eyes off the things of this world and instead focus on God. Fasting is a way to demonstrate to God and to ourselves that we are serious about our relationship with Him. Although fasting in Scripture is almost always a fasting from food, there are other ways to fast. Anything you can temporarily give up in order to better focus on God can be considered a fast (1 Corinthians 7:1-5). Fasting should be limited to a set time, especially when the fasting is from food. Extended periods of time without eating are harmful to the body. Fasting is not intended to punish our flesh, but to focus on God.
In the religions of ancient peoples and civilizations, fasting was a practice to prepare persons, especially priests and priestesses, to approach the deities. In the Hellenistic mystery religions (e.g., the healing cult of the god Asclepius), the gods were thought to reveal their divine teachings in dreams and visions only after a fast that required the total dedication of the devotees. Among the pre-Columbian peoples of Peru, fasting often was one of the requirements for penance after an individual had confessed sins before a priest. In many cultures the practice was considered a means to assuage an angered deity or to aid in resurrecting a deity who was believed to have died (e.g., a god of vegetation).
Thanks for your insight, there are millions of people throughout the world who fast for religious reasons, it is a part of honoring their faith. If someone is fasting to lose weight, improve their health, improve immunity and decrease their insulin sensitivity (or any of the other many health benefits associated with fasting) then yes I agree we promote and encourage you to drink water throughout your fasting days. Why? Drinking water helps keep the body hydrated which is important since we are made up of more than 70% water, it helps you from being dehydrated, which when people feel dehydrated they often feel hungry and want to eat and lastly water helps flush toxins and waste materials from the body. When fasting you will be breaking down waste and other by products so it is important to flush them out of your body; this will also aid your digestion and improve your overall well being.