It's near the very beginning of the section, under "Paco’s Excavation"
Rather than rely on traditional Water Breathing rituals, which do
nothing to keep at bay aquatic predators, Paco used expensive diving bell
lanterns, custom created with Bergeron’s coin. These crystal lanterns,
mounted on iron poles about the size of a hatrack, hold water at bay in
an Area Burst 2. If the lantern is moved, the area of air moves with it. The
enchantment produces fresh, breathable air out of the surrounding water.
The lanterns can last indefinitely, but each must be custom made for
a particular depth and water temperature, and if they’re moved far from
their designated location, their enchantment breaks. (In effect, the PCs
might reverse engineer them, but they cannot be looted.)
EDIT: in case you're playing PF, Area Burst 2 = with a radius of 10 feet