Hydro-Processing Centers are Covenant facilities devoted to the controlling of water flow on terrestrial surfaces, such as Alpha Halo, and most likely to their main colonies. Three separate streams of water flow down into an abyss in the main chamber, with many interconnecting platforms, bridges and walkways hanging dangerously close to the pit. Other rooms are mostly empty, with the exception of Covenant Communication Nodes and Covenant Supply Cases, used by the Covenant before they abandoned the facility because of Flood invasion.
The reason for the Covenant to build this type of facility on a Halo ring is questionable, but it is likely meant to serve as a clean water source for their ground troops. The fact that such a large facility is built in just two to three days is also questionable. It is possible buildings like these are prefabricated for Covenant military uses. Not much else is known about this type of facility.