Quick take
Typical order is pressure tank → iron/sediment treatment as needed → softener → final prefilter → UV → house. Follow the equipment-specific schematic when specialty chemical feed or retention tanks are involved.
Why UV generally comes after softening
Hardness scale can foul the quartz sleeve. Removing hardness upstream can reduce maintenance and preserve UV transmission.
Iron treatment may need to come even earlier
If iron or manganese is present, dedicated treatment usually belongs before the softener and UV to protect both downstream stages.
UV should be close to the final distribution point
Placing UV near the end minimizes the chance that untreated water or fouling stages sit downstream of disinfection.
Do not use UV to solve hardness
UV disinfects; it does not remove calcium or magnesium. Softening and UV address separate problems.