I find it fascinating that these so called experts can make such a claim. If you are trying to disinfect air pollutants you must ensure that the air that is being breathed is forced toward the air ducting systems quickly enough for the air to pass through the device/machine. In order to do this you would need to physically force the air as quickly as possible and the only way of doing this is to use huge fans to direct the air toward machines. It works much the same in water but instead of air-flow, the measurement is based on water-flow. The water must pass the UVC light long enough for the required dose to inactivate the pathogens/bacteria. Enough point is the fact that when a person who is carrying a virus or contagion cough's or sneezes the water droplets carrying the virus will fall on to the surface and only small particles will filtrate through the air. The virus is then contracted by touch.