A hot tub is a large tub or small pool full of heated water and used for soaking, relaxation, massage, or hydrotherapy. In most cases, they have jets for massage purposes. Hot tubs are usually located outdoors, and are often sheltered for protection from the elements, as well as for privacy. Other variants in naming include "Spa", and the trade name "Jacuzzi". These variants can be used to mean an indoor fixture, but a "Hot Tub" is almost always outdoors.
Hot tubs are usually heated using an electric or natural gas heater, though there are also submersible wood-fired heaters, as well as solar hot water systems. Hot tubs are also found at natural hot springs; in this case, the water may be dangerously hot and must be combined with cool water for a safe soaking temperature.
Water sanitization is very important in hot tubs, as many organisms thrive in a warm, wet environment. Maintaining the hot tub water chemistry is also necessary for proper sanitization and to prevent damage to the hot tub. In colder climates, if the hot tub is not used year-round, it should be "winterized" for the off season.
