Ultraviolet disinfection units look much alike and differ in ways that matter a great deal. Comparing them sensibly means ignoring the claims about how many organisms are inactivated, which every compliant unit achieves, and looking instead at flow rating, monitoring, sleeve design and how much the consumables cost over a decade.
Flow rating, honestly interpreted
Every unit is rated for a flow, and that rating is the single most important specification because dose falls as flow rises. Size for the household's peak simultaneous demand rather than its average: a shower, a washing machine and a dishwasher together is the number that matters, not what one tap draws. Manufacturers sometimes publish ratings at more than one dose level, and the higher flow figure corresponds to a lower dose, so compare units at the same dose rather than comparing the headline numbers.
Monitoring separates the serious units
A basic unit tells you the lamp has power. It does not tell you the lamp is still producing useful output, and output falls steadily through the year while the lamp continues to glow. A UV intensity monitor with a sensor in the chamber reports the light actually reaching the water, which catches both an ageing lamp and a fouled sleeve. Better units add an audible alarm and, on the most complete designs, a solenoid that shuts off the supply when the dose falls below specification rather than quietly passing untreated water.
Sleeve, chamber and serviceability
The quartz sleeve separating the lamp from the water fouls with mineral film that blocks the light, and cleaning it is a routine job, so how easily the sleeve comes out matters more than any headline feature. Some designs need the unit removing from the pipework to service; better ones do not. Chamber geometry differs too, and a well designed chamber gives more even exposure at the same flow. Stainless chambers outlast plastic ones. Check that sleeves and O rings are available separately and not only as an assembly.
The cost over ten years
Purchase price is the smaller number. Lamps are replaced annually whether or not they still light, sleeves periodically, and O rings with every sleeve change, so the consumable cost over a decade often exceeds what the unit cost. Compare on that basis and check the lamp is a standard type rather than a proprietary one that ties you to a single supplier at their price. Factor in the pre filtration the unit requires as well, since UV only works on clear water. Our UV bulb replacement guide covers the interval and the routine.
Questions people ask about uv light systems
How do I size a UV system?
To the household's peak simultaneous flow, not its average, and compare units at the same dose level rather than on headline flow figures.
Is a UV monitor worth paying for?
Yes. A power light only proves the lamp is lit. A monitor reports the light actually reaching the water, catching ageing lamps and fouled sleeves.
What maintenance do these need?
An annual lamp change regardless of whether it still glows, periodic quartz sleeve cleaning, and fresh O rings with every sleeve service.
Which cost should I compare on?
Ten year consumables rather than purchase price, and check the lamp is a standard type rather than proprietary to one supplier.