Abstract: A drain inlet vault comprises a plurality of pre-cast concrete vault sections stacked one upon the other to form the vault. Each vault section has essentially the same cross-sectional configuration and at least one perimeter edge that upon stacking the vault sections one on top of the other the perimeter edges of adjacent vault sections engage. A sealant material along the perimeter edges forms a seal as the weight of an upper section bears against a lower section. At least one support element for water treatment equipment, or a component thereof, is mounted between the perimeter edges, and this support element has a portion extending into an interior of the vault for holding the water treatment equipment, or component thereof.