As the hunger strikes in Ireland in 1980 and 1981 showed, a person can last for about 60 days without food.
However, in the desert, one can last for only a few days (depending on physical activity) without water. Further, while death might take a few days in hot conditions, unconsciousness would ensue within a days or so in hot conditions.
Thus, the fast of 40 days by Jesus in the desert must have included water, else He could not have survived the 40 days.
Therefore, thirst was not an issue during this time of Jesus' fasting in the desert - He only lacked food as the verb νηστεύω implies.
Special Case for Ex 34:28
The fact that Moses went for 40 days and 40 nights with either food or water while in the mountain with God cannot be taken as as evidence that people can survive that long. Moses had to climb the mountain and return with heavy tablets of stone - a considerable physical exertion.
However, as is well-known, a human cannot survive much more than a day or two with out water - Moses was obviously miraculously sustained by God while in the mountain for 40 days with even water.