Cauldron's central lake fills the bottom most part of the volcano's caldera. All the drains and sewage of the city flow down eventually to the central lake. The lake drains into the Underdark beneath but in late autumn/winter it's been known to flood the nearest buildings. This is what gave birth to Cauldron's annual Flood Festival.

The lake is periodically cleaned by the clerics of the city's churches in return for charitable donations from the city.