A UV chart can pair different flow limits with different doses and stated water conditions. Do not select its largest GPM number alone. The legacy VIQUA D4 manual pairs ratings with 95% UV transmittance and other conditions; that model was discontinued in 2023. Match the installed model, required treatment, actual water and peak demand with qualified guidance.
A legacy D4 table shows why the rows differ
A product page's prominent flow label may describe only one row of the complete specification. Read the dose, water conditions and footnotes alongside the flow, and establish what treatment your water requires. A large number alone does not establish an appropriate UV system.
VIQUA's D4 page expressly says the model was discontinued on November30,2023. The following is an installed or historical equipment example, not a current purchase recommendation or a rating for other VIQUA models.
The D4 owner manual,603037 RevAM lists these maximum rated flows at 95% UV transmittance:
| Stated UV dose | D4 maximum rated flow at the stated condition |
|---|---|
| 16 mJ/cm² | 23 GPM |
| 30 mJ/cm² | 12 GPM |
| 40 mJ/cm² | 9 GPM |
The same manual says these flow ratings are based on end-of-lamp-life output and a water temperature of 20°C. Its product page's prominent 12 GPM label therefore is not the only flow number, and the 23 GPM row does not promise the dose associated with 9 GPM.
What should you do with the UVT condition?
UVT means UV transmittance. It concerns how the water transmits UV light; a clear-looking glass does not establish that measured value. Keep the rating's stated UVT with the number when discussing capacity.
The D4 manual has a separate water-chemistry section and directs testing of the applicable parameters and appropriate pretreatment. Do not confuse a model's installation criteria with the conditions under which a particular dose-flow row was rated. Have the manufacturer or qualified provider assess your actual water instead of transferring the example's 95% condition to every supply.
Does a dose number establish certification or suitability?
No. NSF's standards explanation distinguishes UV Class A treatment from Class B supplemental treatment of disinfected drinking water. Check the actual model's listing, intended use and operating requirements. A dose row copied from a brochure does not independently establish that classification or every treatment claim.
The UV, carbon and RO comparison describes different treatment purposes. UV capacity is not proof that chemicals or dissolved minerals have been removed.
What should a useful sizing review include?
Provide the installed model and revision, actual water-test findings, required treatment and household peak demand. Ask which complete dose-flow row and operating conditions apply, whether compatible pretreatment is needed and how flow will be kept within the approved arrangement.
Do not adjust controls or add an improvised restrictor to make a chart appear satisfied. Lamp-on alarm assessment and quartz-sleeve maintenance remain separate operating checks. A lit lamp or clean sleeve alone cannot verify the dose being delivered at the current flow. Keep the complete sizing assumptions and commissioning findings with the system.