If God required a fast - was it from food only?

And the LORD said unto Moses, Write thou these words: for after the tenor of these words I have made a covenant with thee and with Israel. And he was there with the LORD forty days and forty nights; he did neither eat bread, nor drink water. And he wrote upon the tables the words of the covenant, the ten commandments. And it came to pass, when Moses came down from mount Sinai with the two tables of testimony in Moses' hand, when he came down from the mount, that Moses wist not that the skin of his face shone while he talked with him. And when Aaron and all the children of Israel saw Moses, behold, the skin of his face shone; and they were afraid to come nigh him. - Exodus 34:27-30

Moses did not eat bread (food) or drink water for 40 days while in God's presence. Surely to survive, and not only survive but to thrive, for 40 days without water is miraculous but it doesn't appear to have been commanded. Perhaps when one is directly in the presence of the Lord certain things become unnecessary for survival. Scripture makes clear that Jesus did not eat for 40 days and is silent regarding any liquid intake.

The law of Moses specifically required fasting for only one occasion—the Day of Atonement (Leviticus 16:29-30; 23:27-31; Numbers 29:7). This custom resulted in calling this day “the fasting day” (Jeremiah 36:6) or “the fast,” (Acts 27:9). It was a very solemn and holy day with a lot of elaborate ritual. (Leviticus 16; Hebrews 10:1-1). Fasting, however, could also be done for other reasons. It was sometimes done as a sign of distress, grief, repentance, or devotion. Fasting was often accompanied by prayer. Also tearing of clothes, throwing dust and ashes upon your head, dressing in coarse sackcloth and uncombed hair and unwashed bodies. - A BIBLICAL PERSPECTIVE OF FASTING

During such a fast only water is permitted. The idea is not to challenge or stress the physical body unto harm but to focus upon the spiritual. Jesus said "When you fast..." and this indicates an expectation that it will occur but it is not an imperative. The focus is God-ward and the imperative is to keep it between oneself and God; not just the degree of the fast but the very fact of it:

Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward. But thou, when thou fastest, anoint thine head, and wash thy face; That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly. - Matthew 6:16-18

There are numerous man-made religious rules regarding when to fast, how to fast, what to fast, etc. and therein lies a danger that we are trying to leverage the Lord or that we are serving ourselves, as if God will hear my prayer because I eat only fish on Friday or because the whole congregation fasts together.

Isaiah has much to say about the fast that the Lord has chosen:

Wherefore have we fasted, say they, and thou seest not? wherefore have we afflicted our soul, and thou takest no knowledge? Behold, in the day of your fast ye find pleasure, and exact all your labours. Behold, ye fast for strife and debate, and to smite with the fist of wickedness: ye shall not fast as ye do this day, to make your voice to be heard on high. Is it such a fast that I have chosen? a day for a man to afflict his soul? is it to bow down his head as a bulrush, and to spread sackcloth and ashes under him? wilt thou call this a fast, and an acceptable day to the LORD? Is not this the fast that I have chosen? to loose the bands of wickedness, to undo the heavy burdens, and to let the oppressed go free, and that ye break every yoke? Is it not to deal thy bread to the hungry, and that thou bring the poor that are cast out to thy house? when thou seest the naked, that thou cover him; and that thou hide not thyself from thine own flesh? Then shall thy light break forth as the morning, and thine health shall spring forth speedily: and thy righteousness shall go before thee; the glory of the LORD shall be thy rereward. Then shalt thou call, and the LORD shall answer; thou shalt cry, and he shall say, Here I am. If thou take away from the midst of thee the yoke, the putting forth of the finger, and speaking vanity; And if thou draw out thy soul to the hungry, and satisfy the afflicted soul; then shall thy light rise in obscurity, and thy darkness be as the noonday: - Isaiah 58:3-10

If we are going to fast for a short period of time from anything in our religious devotion we may fast from whatever we like for as long as we like. What we should do additionally is to take whatever money is saved during the fast, feed the hungry, and tell no one about either the fast or the act of charity:

Take heed that ye do not your alms before men, to be seen of them: otherwise ye have no reward of your Father which is in heaven. Therefore when thou doest thine alms, do not sound a trumpet before thee, as the hypocrites do in the synagogues and in the streets, that they may have glory of men. Verily I say unto you, They have their reward. But when thou doest alms, let not thy left hand know what thy right hand doeth: That thine alms may be in secret: and thy Father which seeth in secret himself shall reward thee openly. - Matthew 6:1-4

Another, more overarching strategy to fasting is to live in such a way that one always has available resources to help those in need whom the Lord brings before us:

Hereby perceive we the love of God, because he laid down his life for us: and we ought to lay down our lives for the brethren. But whoso hath this world's good, and seeth his brother have need, and shutteth up his bowels of compassion from him, how dwelleth the love of God in him? - 1 John 3:16-17

Pure religion and undefiled before God and the Father is this, To visit the fatherless and widows in their affliction, and to keep himself unspotted from the world. - James 1:27

Jesus undertook such a lifelong fast for us. He saw us in need, visited us in our affliction, kept Himself unspotted from the world, and commenced the fulfillment of the Day of Atonement.

I propose the fast that Jesus made in the wilderness was a small description of a time he spent apart from the daily word of God. He walked the world and was tempted by the ways of man, and he overcame all of the temptations placed before him. He had to experience, for himself, the temptations each of us experience every day in order to be able to relate to us, and us to relate to him. The 40 days and nights describe a long period of time which might differ from one individual to another.

Food is something we take in to nourish ourselves in order to live. Food types are different as we have physical food that we ingest through our mouths, and spiritual foods that we ingest through our minds. We can physically live and spiritually be dead.

Matthew 4:

Then Jesus was led by the Spirit into the wilderness to be tempted by the devil. 2 After fasting forty days and forty nights, he was hungry. 3 The tempter came to him and said, “If you are the Son of God, tell these stones to become bread.” 4 Jesus answered, “It is written: ‘Man shall not live on bread alone, but on every word that comes from the mouth of God.'”

Words that come through the mouth of God are spoken words. Spoken words express action. Spoken words express life, and life is what God wants for us.

Jesus Christ is the Son of God. He is the way, the truth and the life.

From my perspective I see that Jesus Christ left the structure of scholars and religious teachers for a period of time, forty days and nights, to be in the world on a walk of faith, taking what he had been taught and knew was true and being tempted by the world of man. He did this in order for us to be able to relate to him. Except for the tempter, he was spiritually alone.

When Jesus was tempted during this time he described himself as bread. The apostle John wrote that Jesus said he is the “bread of life”. The tempter also described people as “stones”, which Jesus also acknowledged and defined as 'man'.

I understand that Jesus took a journey into the world where he was tempted to glorify himself before man. He resisted these temptations so that we could be able to relate to him. He was apart from the teachers and scholars and religious activities like many of us are today.

The world apart from God is a spiritual wilderness.

Fasting, in this instance, is living apart from the spiritual foods of God.

This is what I understand is the answer to your question.

What is the biblical basis to describe fasting required by God? Was it from food only?

Generally speaking Sacred Scriptures simply employs the term fast, when it come to depriving our physical bodies of nourishment of food. However,Scriptures seem to imply that Moses did in fact fast for 40 days from food and drink

The Bible says every little about whether or not water is included or not. That said some do refrain from drinking water during certain hours of the day, while fasting. Water is so vital to our human existence that it would be imprudent to fast from water very long. I believe we can live without water for only three days.

Let us start with what fasting is, in a general sense, shall we:

Fast

In general abstinence from food or drink, a term common to the various Teutonic tongues. Some derive the word from a root whose primary signification means to hold, to keep, to observe or to restrain one's self. The Latin term jejunium denotes an animal intestine which is always empty. Such abstinence varies according to the measure of restriction circumscribing the use of food and drink. Hence it may denote abstinence from all kinds of food and drink for a given period.

As for tradition, we can fast from other things, especially if we are sick and unable to fast from food.

Remember, we are not just bodies and we are not just spirits. We are embodied spirits. Fasting helps us spiritually:

• Strengthens the Will
• Intensifies Prayer
• Fosters Gratitude and Humility

Now back to Scriptures!

St. Paul encourages married couples to abstain from sex so that one may devote oneself to prayer. It must be a mutual choice.

Do not deprive one another, except perhaps by agreement for a limited time, that you may devote yourselves to prayer; but then come together again, so that Satan may not tempt you because of your lack of self-control. - 1 Corinthians 7:5

Longer fasts are abstaining of food items and not water. The maximum length of an adult fast that is biblically supported is forty days without food for a male adult in good health, and three days without water. The Bible does not speak of children engaging in fasting food.

Go, gather together all the Jews that are present in Shushan, and fast ye for me, and neither eat nor drink three days, night or day: I also and my maidens will fast likewise; and so will I go in unto the king, which is not according to the law: and if I perish, I perish. - Esther 4:16

This passage also reminds me of the Fast of Nineveh which commemorates the three days that Prophet Jonah spent inside the belly of the Great Fish and the subsequent fast and repentance of the Ninevites at the warning message of the prophet Jonah according to the bible.

Jesus, Elijah and Moses all fasted 40 days. In all three cases water is not mentioned.

Jesus Is Tested in the Wilderness

4 Then Jesus was led by the Spirit into the wilderness to be tempted[a] by the devil. 2 After fasting forty days and forty nights, he was hungry. 3 The tempter came to him and said, “If you are the Son of God, tell these stones to become bread.”

4 Jesus answered, “It is written: ‘Man shall not live on bread alone, but on every word that comes from the mouth of God.’[b]”

5 Then the devil took him to the holy city and had him stand on the highest point of the temple.

6 “If you are the Son of God,” he said, “throw yourself down. For it is written:

“‘He will command his angels concerning you, and they will lift you up in their hands, so that you will not strike your foot against a stone.’”

7 Jesus answered him, “It is also written: ‘Do not put the Lord your God to the test.’[d]”

8 Again, the devil took him to a very high mountain and showed him all the kingdoms of the world and their splendor. 9 “All this I will give you,” he said, “if you will bow down and worship me.”

10 Jesus said to him, “Away from me, Satan! For it is written: ‘Worship the Lord your God, and serve him only.’[e]”

11 Then the devil left him, and angels came and attended him. - Matthew 4:1-11

Elijah fasted for forty days, but it does not say that never took water! It seems to be implied though.

Elijah at Mount Horeb (Sinai)

19 King Ahab told Jezebel everything that Elijah did and how Elijah had killed all the prophets of Baal with a sword. 2 So Jezebel sent a messenger to Elijah and said, “I swear that by this time tomorrow, you will be just as dead as those prophets. If I don’t succeed, may the gods do the same or worse to me.”

3 When Elijah heard this, he was afraid. So he ran away to save his life. He took his servant with him, and they went to Beersheba in Judah. Then Elijah left his servant in Beersheba 4 and walked for a whole day into the desert. Then he sat down under a bush and asked to die. He said, “I have had enough, Lord! Take my life. I am no better than my ancestors.”

5 Then Elijah lay down under the bush and went to sleep. An angel came to him and touched him. The angel said, “Get up and eat!” 6 Elijah looked around, and by his head there was a cake that had been baked over coals and a jar of water. He ate and drank and then went back to sleep.

7 Later the Lord’s angel came to him again, touched him, and said, “Get up and eat! If you don’t, you will not be strong enough to make the long trip.” 8 So Elijah got up. He ate and drank and felt strong. Then Elijah walked for 40 days and nights to Mount Horeb, the mountain of God. - 1 Kings 19

It seems that Moses did abstain from both food and water.

And he was there with the Lord forty days and forty nights; he neither ate bread nor drank water. And He wrote upon the tablets the words of the covenant, the Ten Commandments. - Exodus 34:28

Thus whether or not Jesus fasted from both food and water or from just food is an open question. It could be noted that the time of the year may be of some importance here. Abstaining from water in summer is much harder than in winter.

It is evident, that Jesus, Elijah and Moses were suppopted in some miraculous way during their fasts. It is generally believed that normal human beings can not live past three days without water or seven days without food.