Accumulations of pigeon droppings can contain pathogens and should be removed by a specialized firm. Salmonella, campylobacter bacteria, chlamydia strains, cryptococci and pigeon ticks are listed as being possible pathogens. On this photo the accumulation of droppings is still at an early stage.
Legionella (Potable Water Supply, Ventilation)
If water is left in a cold water pipe over several tens of days it will stagnate. Iron oxides will colour the water and there is an enhanced risk of legionella growth as well as the increase of other bacteria. If high levels of legionella exist within the cold water cycle there is enhanced risk of it being transferred to the hot water system. This ultimately leads to a health risk when building occupants take a shower and inhale aerosols.
Potable cold water and hot generation systems need to be safe from any heath risk due to legionella. According to the Drinking Water Ordinance (Trinkwasserverordnung [§ 14 Abs. 3]) landlords of multifamily residential houses and owners / operators of businesses for the public (e.g. Hotels, Hospitals, Saunas) are required to have their hot water generation systems tested for legionella at several representative sampling locations.