Potential sources of such contaminated water include cooling towers (some 40% to 60% of ones tested) used in industrial cooling water systems as
well as in large central air conditioning systems, evaporative coolers, nebulizers, humidifiers, whirlpool spas, hot water systems, showers,
windshield washers, architectural fountains, room-air humidifiers, ice making machines, misting equipment, and similar disseminators that draw
upon a public water supply.
The disease may also be transmitted from contaminated aerosols generated in hot tubs if the disinfection and maintenance program is not done
rigorously. Freshwater ponds, creeks, and ornamental fountains are potential sources of Legionella. The disease is particularly associated
with hotels, fountains, cruise ships and hospitals with complex potable water systems and cooling systems.
The guidance issued by the UK government's Health and Safety Executive (HSE) now recommends that microbiological monitoring for wet cooling systems,
using a dipslide, should be performed weekly. The guidance now also recommends that routine testing for legionella bacteria in wet cooling systems be
carried out at least quarterly, and more frequently when a system is being commissioned, or if the bacteria have been identified on a previous
Further non-statutory UK guidance from the Water Regulations Advisory Scheme now exists for pre-heating of water in applications such as solar water
heating systems. www.wras.co.uk...
The City of Garland, Texas requires yearly testing for legionella bacteria at cooling towers at apartment buildings.
Malta requires twice yearly testing for Legionella bacteria at cooling towers and water fountains. Malta prohibits the installation of new cooling
towers and evaporative condensers at health care facilities and schools.
The Texas Department of State Health Services has provided guidelines for hospitals to detect and prevent the spread of nosocomial infection due to
legioneCopper-Silver ionization is an effective industrial control and prevention process to eradicate Legionella in potable water distribution
systems and cooling towers found in health facilities, hotels, nursing homes and most large buildings. In 2003, ionization became the first such
hospital disinfection process to have fulfilled a proposed four-step modality evaluation; by then it had been adopted by over 100 hospitals.
Additional studies indicate ionization is superior to thermal eradication.
A 2011 study by Lin, Stout and Yu  found Copper-Silver ionization to be the only Legionella control technology which has been validated through
a 4 step scientific approach.