Ultraviolet (UV) disinfection

A UV system passes water past an ultraviolet lamp that inactivates bacteria, viruses and cysts such as Giardia and Cryptosporidium. It adds no chemicals and removes nothing: lead, PFAS, nitrate, arsenic, iron and hardness all pass straight through.

It is the most common way to disinfect private well water continuously. It only works on clear, pre-treated water, and it needs a lamp change every year.

How it works

Water flows through a stainless steel chamber around a lamp housed in a quartz sleeve. UV-C light damages the genetic material of microorganisms so they cannot reproduce. How well it works depends on the dose, measured in millijoules per square centimeter (mJ/cm2), which falls when flow is high or the water is cloudy.

Flow ratings depend on the dose used to calculate them. SpringWell’s 2019 BlackComb manual, for example, rates its reactor at 15 gpm at 30 mJ/cm2, but 12 gpm at 40 mJ/cm2, the Class A dose. Check which dose a flow rating assumes.

UV also leaves no residual. Penn State Extension notes it “only kills bacteria inside the unit” and does nothing for bacteria that survive or are introduced into the plumbing afterward.

What it removes and what it does not

With pre-filtered water, the CDC says UV treats parasites, bacteria and viruses. It does not remove chemicals.

Penn State adds a limit: UV is not recommended where total coliform bacteria exceed 1,000 colonies per 100 mL or fecal coliform exceed 100 colonies per 100 mL. At that level, find and fix the source first. Shock chlorination is the usual first step.

UV does nothing for PFAS, lead, nitrate, arsenic, iron, hardness or chlorine. If your test shows any of these, you need another treatment in front of the UV, or a point-of-use option such as reverse osmosis for drinking water.

Certifications to look for

The standard is NSF/ANSI 55, and its two classes are very different:

• Class A: delivers at least 40 mJ/cm2 and is intended to inactivate bacteria, viruses, Cryptosporidium and Giardia in contaminated but visually clear water. It must include a UV sensor and alarm as a fail-safe.
• Class B: a lower dose (16 mJ/cm2) for supplemental treatment of disinfected public water or other water already tested acceptable. It is not meant for contaminated water.

Of the UV units we track, only Aquasana’s is certified, to Class B by NSF at 6 gpm. SpringWell’s UV and US Water Systems’ Pulsar claim no NSF/ANSI 55 certification. For a well, a Class A listing is the one to look for; without it, confirm the unit has a sensor and alarm and that the flow rating is quoted at 40 mJ/cm2.

Installation and upkeep

UV goes last in the treatment train, after sediment, iron and softening equipment, because Penn State says the water must be “completely clear and free from any suspended sediment or turbidity.” Makers set specific limits: SpringWell requires iron under 0.3 ppm, hardness under 7 grains per gallon and tannins under 0.1 ppm; Aquasana adds manganese under 0.05 ppm and turbidity under 1 NTU.

It needs a grounded outlet but no drain. Upkeep:

• Lamp: about once a year. Penn State says lamps slowly lose intensity; US Water Systems rates its lamps at 9,000 hours.
• Quartz sleeve: clean regularly, since hardness and iron coat it.
• Electricity: Penn State estimates $2 to $4 a month.

UV cannot reach bacteria already in the plumbing downstream. Penn State suggests shock chlorination as the first step when a well tests positive for bacteria. See chemical injection for continuous chlorination as the alternative to UV, and our well testing guide for retesting.

Costs

HomeGuide puts UV systems at $350 to $1,500 installed and replacement lamps at $20 to $100. Prices checked September 2026:

System	Flow	Price	Lamp
US Water Systems Pulsar	10 to 20 gpm	$995 to $1,195	$111 to $119 a year
SpringWell UV	15 gpm (at 30 mJ/cm2)	$1,101	$119 a year
Aquasana Rhino Well Water with UV	7 gpm system; UV certified Class B at 6 gpm	$1,749 with carbon tank	$126 a year

Over 10 years, SpringWell’s unit comes to about $2,290 with lamps. See our well water picks and the product finder.

Pros and limits

Pros

• Inactivates bacteria, viruses and cysts without chemicals.
• No taste, odor or byproducts.
• Low running cost and no drain needed.

Limits

• Removes no chemicals, metals or minerals.
• Needs clear water: sediment, iron, manganese and hardness must be treated first.
• No residual protection in the plumbing.
• Annual lamp replacement, and it stops working if the power fails.
• None of the whole-house UV units we track is Class A certified.