Amid the harsh realities of warfare and the confinement of a fortress, a deep sense of nostalgia takes hold of David. He experiences a profound longing for his hometown and the familiar comforts of his past, expressing an intense and emotional craving [מצודת ציון].
The primary approach among commentators is that his request stemmed from a genuine physical need. The events took place during the harvest season when the weather was intensely hot, leaving David yearning for cold, refreshing water [רד״ק, מצודת דוד]. It is likely that the fortress where he was stationed lacked quality drinking water [רד״ק]. His specific craving for the well of Bethlehem was born out of habit, as he had recently lived there [מלבי״ם], or perhaps it was a wistful longing for the sweet water he remembered drinking as a child [ביאור שטיינזלץ].
When David voiced his desire for water, he was not issuing a command to his troops. Rather, he was simply expressing a heartfelt wish, hoping aloud that such cool water might somehow be found [מצודת דוד]. However, when three of his warriors actually risked their lives to fulfill this wish, David felt deep regret. He was pained that his men had placed themselves in such severe danger merely to satisfy his physical craving [רד״ק].
In contrast to this literal understanding of physical thirst, an ancient Rabbinic tradition offers a completely different dimension to the story. According to this approach, David was not seeking actual water to drink at all. Instead, he was grappling with a complex matter of Jewish law and was asking for legal guidance from the high court of the Sanhedrin, which was in session at the city gate of Bethlehem at that time [רש״י].