Annual kWh ≈ system watts × 8.76. A 40W system uses about 350 kWh/year; a 50W system about 438 kWh/year. Multiply annual kWh by your electricity rate to estimate yearly cost.
Use this formula for yearly electricity cost
Annual kWh = system watts × 8,760 hours ÷ 1,000. Then multiply annual kWh by your electricity price per kWh.
Examples: 25W ≈ 219 kWh/year; 40W ≈ 350 kWh/year; 50W ≈ 438 kWh/year; 80W ≈ 701 kWh/year. At $0.15/kWh, a 50W system is about $65.70/year. At $0.25/kWh, the same system is about $109.50/year.
A real whole-home benchmark: VIQUA D4
VIQUA publishes a 50W maximum power-consumption figure for its D4-family whole-home UV systems, with a 40W lamp. Its current UV overview also describes a typical whole-home system as using roughly the power of a 40-watt light bulb.
That makes the 40W–50W range a useful real-world benchmark, but always use the rated input power of your exact controller/system rather than the lamp wattage alone when estimating electricity cost.
Why UV systems normally stay on 24/7
A whole-home UV reactor has to be ready whenever water flows. Cycling it off simply to save a few dollars can create periods when water passes without the intended UV treatment. Follow the manufacturer operating instructions for the exact system rather than treating it like a light you switch on only when needed.
Electricity is only one ownership cost
Lamp replacement, quartz-sleeve cleaning or replacement, pretreatment cartridges and professional service can matter more than the electricity bill. Compare total annual ownership cost, not watts alone.
Pretreatment can matter more than shaving a few watts
Turbidity, iron, manganese and hardness scale can reduce UV transmission or foul the sleeve. Correct upstream treatment can protect disinfection performance and reduce maintenance problems even though it adds its own operating cost.
Decision checklist for How Much Electricity Does a UV Water Filter Use? 2026 Cost Guide
Define the exact problem this purchase needs to solve, then compare products on evidence, capacity and long-term ownership rather than marketing labels alone. Verify the specifications that materially affect the result and make sure they apply to the exact model being considered.
Include installation, replacement parts, consumables and maintenance in the comparison. A product that is cheaper on day one can cost more over several years if it uses short-life proprietary parts or requires professional service that a competing design avoids.