Legionella bacteria is a serious problem, but can be avoided if owners of swimming pools, hot tubs, and whirlpool spas keep them cleaned on a regular basis. The manager of a local pool and spa dealership says one of the biggest problems can be found with rental beach homes. That's because pools and spas at these rental units are rarely cleaned on a weekly basis. Different people leave different germs and bacteria that thrive in this source of water. Experts say to kill most contaminants, you need certain pool cleaning chemicals which are available at most places where pool supplies are sold. There is also a filter that you put inside of a hot tub or pool's filter to help treat the water.