Ultraviolet is often described as cheap to run, and compared with chemical disinfection it is. But the running cost is not zero and it is not optional, because a UV system that is not maintained is not treating water while continuing to look exactly like one that is. Costing it honestly means counting four items, only one of which is the equipment.
The equipment and its installation
The unit itself is a chamber, a lamp, a quartz sleeve and a controller, and the price varies mainly with the flow rate it is validated for and whether it carries an intensity sensor. Installation adds plumbing into the point of entry, isolation valves, a reliable power supply and, where specified, a solenoid shut off valve. Buying a unit rated for the household's peak draw rather than its average is the decision that costs a little more at purchase and prevents the most common performance failure.
The annual consumables
A lamp every year, regardless of whether it still glows, because germicidal output fades long before the light does. A sleeve o-ring at the same visit, since it is the seal keeping water out of the lamp chamber. And the pretreatment filters, which are usually the larger of the two costs: sediment cartridges on schedule, plus whatever iron, manganese or hardness treatment the water needs, because all of those film the sleeve and cut the delivered dose. Electricity for a lamp running continuously is modest by comparison.
Testing, which is the item people leave out
The EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, so no utility is sampling on your behalf, and a UV system produces no evidence of its own success. That makes periodic laboratory testing part of the cost of ownership rather than an optional extra: once after commissioning to confirm the installation works, and periodically after that. It is the only thing that closes the loop between equipment that appears to run and water that is actually being treated.
How it compares
Against continuous chlorination, ultraviolet is simpler, adds nothing to the water and needs no solution to mix, but it does not oxidize iron or sulfur, does not deal with iron bacteria, and leaves no residual protecting the plumbing downstream. Against bottled water it is far cheaper. Against doing nothing on a well with a positive bacteria result, it is the standard answer. Our water softener cost guide covers the hardness treatment that often sits in the same train and shares the same installation visit.
Questions people ask about uv water system
What does a UV system cost to run each year?
A lamp, a sleeve o-ring, the pretreatment filters and modest electricity. The pretreatment is usually the larger part of the ongoing cost.
Can I skip the annual lamp change to save money?
No. Output fades well before the lamp goes dark, so a system with an old lamp looks identical to a working one while treating far less.
Is water testing really necessary once it is installed?
Yes. The system produces no evidence of its own success, so a test after commissioning and periodically afterwards is the only confirmation.
How does it compare with chlorination?
Simpler and chemical free, but it does not oxidize iron or sulfur, does not deal with iron bacteria, and leaves no residual in the plumbing.