UV Water Purifiers: How UV Works, and When It Is Enough

UV effectiveness is a function of dose — intensity multiplied by contact time, measured in mJ/cm². Adequate dose depends on the organism, and protozoan cysts need considerably more than bacteria.

Critically, UV only works on water it can penetrate. Turbidity, suspended solids and iron all absorb or scatter UV, and organisms can shelter behind particles. This is why UV always sits after filtration, never before it, and why a UV purifier on visibly cloudy water is not doing what its rating claims.

• A sediment pre-filter ahead of the lamp is not optional — it is what makes the UV dose meaningful.
• Scale and iron deposits on the quartz sleeve cut transmitted intensity sharply. Clean the sleeve at each service.
• Higher flow rate means less contact time and therefore lower dose. Do not exceed the rated flow.
• A lamp that is on is not necessarily a lamp that is working — output declines with age well before failure.

UV and UF are complementary rather than competing. UV inactivates organisms but leaves their bodies in the water and offers no barrier if the lamp fails. UF is a physical membrane that blocks bacteria and cysts, works without electricity, and keeps working when the lamp does not.

For low-TDS supply, UV+UF together is the configuration we recommend: the UF membrane is a fail-safe barrier, and the UV handles what passes through. It also means a power cut does not leave you unprotected.

• UV lamp: replace every 9,000–12,000 hours, in practice roughly annually. Cost ₹500–₹1,500.
• Quartz sleeve: clean at every service; replace if etched or clouded.
• Sediment pre-filter: every 6–12 months — this protects UV effectiveness directly.
• Carbon filter (if fitted): every 6–12 months for taste and chlorine.
• Check the lamp-status indicator regularly. Some purifiers will keep dispensing with a failed lamp, which is silent failure.