The Hydro Impact Basin (HIB) holds about 3.4 million liters of water. This is based on the stated dimensions of 20 feet deep by 100 feet long by 60 feet wide, measured at the water surface. To compare, the average 21-foot round swimming pool with a depth of 48 inches holds 51,100 liters. This means that the HIB is about 66 times larger! An Olympic swimming pool holds 2.5 million liters of water, which means the HIB is still about 1.4 times the size.
The HIB is, in fact, filled with a hose:
I haven’t found any information about water consumption, but I did find that operational costs are constrained:
Operational costs (water consumption, grounds maintenance, labor to
operate/maintain basin) shall be considered and controlled to a range of
\$2,000 to \$2,500 per year, not including actual testing activities.
I also haven’t found whether any other space vehicles will use the HIB (my guess is not), but Orion does get to share the pool with divers who can access the pool from ladders and stairs around the perimeter. The divers standby to assist with recovery in the event of a sinking vehicle.