Most residential home do not have enough hot water supply to fill an Ofuro. With every cubic foot of water being 7 gallons, smaller Ofuros hold about 100 gallons and a “typical” 5′ x 3′ x 26″ deep Ofuro holds about 160 gallons.
Some instantaneous water heaters can fill an Ofuro, but most people chose to add a small recirculation (pump) system with an electric “spa” heater. Adding a filter and ionizer to this, one can reuse the water for up to a week without the use of standard hot tub chemicals. Using a small amount of chemicals the water can last up to 3 months.