John Gill 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)

For all the wells which his father's servants had dug, in
the days of Abraham his father
For the watering of his flocks and herds, see (Genesis 21:25) : the Philistines had stopped them, and filled them with earth ;
that they might be of no use; and this they did through envy to him, and is mentioned as a proof of it.