Keluaran 7:24

7:24 All the Egyptians dug around the Nile for water to drink, ¹  because they could not drink the water of the Nile.

Keluaran 13:22

13:22 He did not remove the pillar of cloud by day nor the pillar of fire by night from before the people. ² 

[7:24]  ¹ sn The text stresses that the water in the Nile, and Nile water that had been diverted or collected for use, was polluted and undrinkable. Water underground also was from the Nile, but it had not been contaminated, certainly not with dead fish, and so would be drinkable.

[13:22]  ² sn See T. W. Mann, “The Pillar of Cloud in the Reed Sea Narrative,” JBL 90 (1971): 15-30.