When being humidified with nozzle systems, water is atomized out into the room where the wish to control the air humidity exists. It is of vital importance that the water being used is clean and bacteria-free, thus no health risk to the people being in the humidified rooms can occur.

Water is an important foodstuff, and many bacteria are naturally living in water-supported systems or can adhere to water-aerosols.

For the time being, no public authority requirements on control of water quality for humidification systems exist, and there are no standards of how many CFU are allowed in water for humidifying purposes. There are standards concerning CFU in drinking water and how drinking water must be controlled, but the standards and the drinking water requirements cannot be transferred directly to humidification systems, as the water is not consumed, but is evaporated and absorbed into the air.

In Germany guidelines concerning number of CFU in air and water exist, and these guidelines are to be observed when installing humidification systems in industrial rooms.

To ensure that the water atomized from humidification systems cannot involve any risk, certain measures are to be taken. This implies that the humidification system has to be built up in a hygienic design and that hygienic precautions are to be taken, partly concerning production and installation of the systems, partly concerning subsequent use, service and maintenance.