Quick take
Many residential UV manufacturers call for lamp replacement about once per year. Clean the quartz sleeve and follow the exact system schedule rather than waiting for the lamp to burn out.
Why annual replacement is common
Low-pressure mercury UV lamps gradually lose germicidal output even while visible light remains.
Quartz sleeve maintenance
Mineral scale or fouling on the sleeve can block UV transmission and reduce effective dose.
Pretreatment matters
Iron, manganese, hardness and turbidity can interfere with UV performance, which is why well-water systems often need upstream treatment.
Do not use appearance as the indicator
A glowing lamp is not proof that the UV intensity is still adequate. Use the manufacturer interval, alarm or sensor.