Improving upon the industry standard, D1® offers the patented UltraPure® water management system. UltraPure® is more than just an ozone generator; it’s a fully engineered water management system similar to the systems used throughout European municipal waste facilities. This hot tub filtration system mixes ozone and water three times to ensure ozone comes in contact with every drop of water to provide the purest water possible, 24 hours a day. That means the water is not just clean, it’s crystal clear. The best part is, UltraPure® silently purifies while you’re in the tub for an exceptionally quiet experience. US Patent: 5,665,228