The issue is that ozone purification cleans the water at the source, but it's free to pick up contamination in the pipes as it makes its way to the tap; chlorination works right up until the water is drunk. The downside is that chlorinated water does not taste great.

If one has a good pipe system, the ozonated water is fine. If there's any worry, though, chlorinated is safer. I'm not surprised that a military base would choose the safer alternative: no-one ever got fired for ensuring that the water is safe to drink.