Albert Barnes Commentary 1 Samuel 29:1

"Now the Philistines gathered together all their hosts to Aphek: and the Israelites encamped by the fountain which is in Jezreel." — 1 Samuel 29:1 (ASV)

A fountain - This is probably the fine spring of Ain-Jalud. It is impossible to say what specific circumstances led to the conflict between Israel and the Philistines taking place so far north in the plain of Jezreel. It was possibly connected with movements of the Aramean tribes to the north of Palestine (See 2 Samuel 8).