From Halopedia, the Halo wiki
Hydro-processing centers are Covenant facilities devoted to processing water for the purposes of powering and refueling their capital ships. As Covenant starship pinch fusion reactors use the hydrogen isotopes deuterium and tritium for fuel, the process likely involves isolating the said isotopes from water.
One such facility was located on Buwan, the primary natural satellite of the Unggoy homeworld, Balaho. Though abandoned following the fracturing of the Covenant, the facility continues to operate through its automated subsystems.
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, except for Covenant communication nodes and Covenant supply cases.
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