[76] Portugal Argentina Poland 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.
[82] The City of Garland, Texas, United States requires yearly testing for legionella bacteria at cooling towers at apartment buildings.
[84] The Texas Department of State Health Services has provided guidelines for hospitals to detect and prevent the spread of nosocomial infection due to legionella.
This group has published guidelines[87] about the actions to be taken to limit the number of colony forming units (i.e., the "aerobic count") of micro-organisms per mL at 30 °C (minimum 48 hours incubation): Almost all natural water sources contain Legionella and their presence should not be taken as an indication of a problem.
[citation needed] Copper-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.
"[91] In 2010 a study by the UK Health Protection Agency reported that 20% of cases may be caused by infected windscreen washer systems filled with pure water.