Cases of Legionnaires' disease have been linked to many types of equipment that contain water, but plumbing systems and air conditioning systems are most often blamed. Although it is possible to contract the illness from legionellae growing in home plumbing systems, most cases have been traced to large buildings. This may be because larger piping networks are generally more conducive to legionellae growth. Also, the air conditioning systems for large buildings often include cooling towers, which contain a pool of warm water in which legionellae can flourish.