In contrast to a typical bathtub, a hot tub is designed to be used by more than one person at a time, with many models accommodating four or more people. Hot tubs are usually located outdoors, although they can be installed indoors. Also, the water in a hot tub is not changed with each use, but is kept sanitary using methods similar to those used for swimming pool sanitation. Another difference between baths and hot tubs is that soaps and shampoos are not used in wet-jetted hot tubs (although they can be used in air-jetted hot tubs).