Charles Ellicott Commentary Genesis 26:15

"Now all the wells which his father`s servants had digged in the days of Abraham his father, the Philistines had stopped, and filled with earth." — Genesis 26:15 (ASV)

The wells. — In the East, the digger of a well is regarded as a public benefactor. However, the Philistines stopped those that Abraham had dug, probably because they regarded his possession of them, though confirmed by the covenant between him and Abimelech (Genesis 21:32), as an intrusion upon their rights as the people of the country.

Also envious of the rapid increase of an alien’s wealth, they determined to drive Isaac away. For this purpose, no means would be more effective than preventing him from obtaining water for his cattle.

Following this, an express command came from the king for Isaac to depart, which he obeyed. He had sought refuge there because of the famine and had no right to continue in Gerar if the people refused their hospitality.