Midrash su Geremia 14:3

And they went three days in the wilderness, and found no water (Exod. 15:22). Some say that the water they had taken with them, from between the rocks, was exhausted by that time. Why does the Scripture say and found no water? Because there was no water even in their water containers, as is said in the verse: And the nobles send their lads for water; they come to the pits, and find no water; they are ashamed and confounded, and cover their heads (Jer. 14:3). Those who interpret the words of the Torah metaphorically hold that they had abstained from studying the Torah, which is compared to water, as it is written: Ho, everyone that thirsteth, come ye for water (Isa. 55:1).

(Exodus 15:22) "And they went out to the desert of Shur": This is the desert of Kazav. They said about the desert of Kazav that it was nine hundred parasangs by nine hundred parasangs — all full of serpents and scorpions, viz. (Devarim 8:15) "… who led you in the great, awesome desert of snake, fiery serpent, and scorpion, etc." And it is written (Isaiah 21:1) "A prophecy of the desert of the sea, etc.", and (Ibid. 30:6) "A prophecy of the beasts of the south in a land of affliction and oppression, lavi and layish (types of lions) among them, efeh and flying serpent, etc." "efeh" is a viper. It was said about this viper, that when it sees the shadow of a bird flying in the air and "links up" with its shadow, its limbs descend, in spite of which (Jeremiah 2:6) "they did not say 'Where is the L rd who brought us up from the land of Egypt, who led us through the wilderness, a land of deserts and pits, a land of drought and tzalmaveth?'" What is "tzalmaveth"? "tzel" (a shadow) and (i.e., accompanied by) "maveth" (death). R. Akiva said: This was told to me by Rabbeinu Hakadosh (Rebbi): There was a man in Eretz Yisrael called "Merutah" ("torn"). Once he climbed a hill to collect wood, and he saw the snake, but the snake did not see him, when at once the hair of his head fell out and he had no hair until the day of his death — wherefore he was called Merutah." (Exodus 15:22) "and they went in the desert for three days without finding any water": R. Yehoshua says: This is to be taken literally. R. Elazar says: Wasn't there water under the feet of the Israelites, the earth floating on water, viz. (Psalms 136:6) "He spread the earth over the water"? (i.e., they could dig for it). What, then, is the intent of "without finding any water"? __ (He made them dig) in order to weary them (to test their faith). Others say: The water that Israel had taken in their vessels between the clefts (in the Red Sea) gave out at that time. What is the intent, then, of "without finding water"? Even in their vessels, as in (Jeremiah 14:3) "Their nobles sent their youths for water. They came to the cisterns, but found no water. They returned, their vessels empty." The expounders of metaphors said: They did not "find" words of Torah, which are compared to water. Where is this seen? (Isaiah 55:1) "Ho! all who thirst, go to the waters!" Because they separated from words of Torah for three days, they rebelled — wherefore the prophets and the elders instituted that they read in the Torah on Sabbath, Monday, and Thursday. How so? They read on Sabbath and pause on Sunday; they read on Monday and pause on Tuesday and Wednesday; they read on Thursday and pause on Friday (so that they do not go three consecutive days without reading Torah.)