Hydraulic equipment leaks. On ordinary ground that is a maintenance item. On a dam, at a filtration plant, or beside a reservoir, a leak is a water-quality event — so the fluid is part of the risk picture, not just a consumable.
Panolin is readily biodegradable and lasts far longer than conventional oils when it is kept properly filtered, which means fewer drain-downs, fewer people working on the equipment, and fluid that breaks down rather than persists if it ever reaches the water.
Reliability you can schedule around. Chemistry you can trust near drinking water.