No, the Ultraviolet water disinfection system should not be turned off whether you or your family are using the water or not. In addition to killing bacteria, the light creates a barrier between the disinfected water and the untreated water. By leaving the UV system on, you eliminate the potential problem of having bacteria grow through the system while the unit is off and re infecting the water downstream of the UV system. When you turn the UV back on, yes it will kill the bacteria inside the chamber but it won’t kill the bacteria downstream of the UV. Turning the UV on and off when you’re away gives your family a false sense of security.
However, if you drain the water from your UV purification system, for example during winterization, the UV system must then be switched off. During other long periods of non-use, for a vacation home for example, the UV system can be shut off to save power and lamp life provided shut off valves are used on either side of the UV system creating a physical barrier to keep the untreated water or bacteria from passing through the UV chamber while not in use.
The lamps age regardless of the amount of water drawn through the system, you will need to replace the lamp after 12 months or 9,000 hours of use. Another important reason to not continually turn the UV system on and off is that it will severely shorten the life span of the ballast or controller. The same is also true if you leave the lamp in the UV system for longer than 12 months.