Faced with an impending siege, the residents of Jerusalem launch into frantic military and practical preparations to fortify their city. However, their efforts are entirely physical, trusting only in their own defenses rather than turning back to God [שד"ל].
The city's defenses are severely compromised by cracks and broken sections that have multiplied throughout the walls of Zion. These gaps create dangerous security vulnerabilities, leaving the city exposed to an easy conquest [רש"י, מצודת דוד, רד"ק]. Another perspective suggests these broken sections represent the future damage the enemy is expected to inflict using siege ramps [אברבנאל].
To counter this threat, the people focus their efforts on the city's water systems, specifically an artificial, stone-built, and lime-plastered reservoir designed to catch rainwater [רד"ק, מצודת ציון, אברבנאל]. This particular reservoir is located close to the city wall [מצודת דוד], or perhaps it is identified as the lower one simply to distinguish it from another reservoir situated higher up in the area [אברבנאל].
The commentators offer several explanations for the intense activity surrounding this water source. The primary approach among commentators is that the residents collect scattered water into the reservoir to mix mortar and clay, allowing builders to seal the broken walls and rebuild the city's defenses [מלבי"ם, מצודת דוד, רד"ק, אברבנאל]. Others explain that the goal is to bring the water safely inside the city limits, deliberately depriving the besieging enemy of any water sources outside, much like King Hezekiah's historic strategy of stopping up the local springs [שד"ל, ביאור שטיינזלץ]. A different strategy suggests the water is intentionally channeled into a trench surrounding the city, creating a protective moat to hold back the enemy forces [אבן עזרא, אברבנאל]. Finally, a completely different understanding shifts the focus from the water to the people themselves. In this view, it is the citizens who gather at the lower reservoir. Because this area sits so close to the broken sections of the wall, it represents a critical weak point that requires the people to mass together to provide heavy military defense [רש"י].