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

>Then Jesus was led up by the spirit into the wilderness to be tempted by the devil. 2 And after he had fasted for forty days and forty nights, he then became hungry. Matt 4:1-2 Jesus was hungry - says nothing about being thirsty, which would usually be a more urgent need. This example of perhaps the most significant fast in the bible, appears to have been of food only. Further we read that the first temptation was, >If you are the Son of God, tell these stones to become *bread*. Is there a definite description of what kind of fasting God requires - specifically when he *requires a fast* as opposed to a time without food etc for other purposes or reasons.