UV Water Filter: The Complete Guide to UV Water Disinfection

A UV light is a stainless steel chamber with a lamp inside it. Your well water flows past the lamp, and the light kills the bacteria in it, coliform and E. coli included, before the water reaches a single faucet. It adds nothing to the water and removes nothing else, so it only works on clear water, and it goes after the sediment filter and anything that takes out iron or hardness.

Every well needs a UV light, in my opinion, and a lab report that says coliform is present settles it. This guide covers how the light works, what it kills (the parasites Giardia and Cryptosporidium included), what has to come out of the water first, where it goes, what your plumber needs to know, the yearly lamp, and what it costs to run.

How UV Water Disinfection Works

A UV light kills germs while the water flows past the lamp, so they are dead before the water reaches any faucet. The lamp's 254 nanometer UV-C light damages the DNA of bacteria, viruses and parasites, so they cannot multiply.

The lamp sits inside a clear quartz glass tube called the sleeve, so the water never touches the lamp itself. Nothing is added to the water and nothing is taken out.

Two things you control set the dose: how fast the water moves past the lamp, and how clear it is. An old lamp or a filmed-over sleeve lowers it too. That is why VIQUA rates each unit at a flow for each dose (the table is under sizing), and why the water has to be clear going in.

The controller counts the lamp's life down from 365 days, beeps when the lamp is due, and sounds an alarm if the lamp fails. Neither the VH200 nor the VH410 has a sensor that measures the light reaching the water; in VIQUA's lineup, only the monitored VH410M carries one.

My review of the VH410 (3:13). In it I say 19 gallons a minute; VIQUA rates the VH410 at 18 at its standard dose, and that is the number to use.

What a UV Light Kills

A UV light kills what is alive in the water: bacteria such as coliform and E. coli, viruses, and parasites such as Giardia and Cryptosporidium. VIQUA's own list for its units names cryptosporidium, giardia, pathogenic E. coli, campylobacter, legionella, salmonella, shigella, norovirus, enterovirus and hepatitis A, and VIQUA says it showed this in its own testing.

The CDC says the same thing about UV systems in general: they do not remove chemicals, and they work better when the water is filtered first. If your test also shows lead, arsenic, nitrates or PFAS, each one needs its own treatment; carbon filters handle many of the chemicals.

What Kills Cryptosporidium in Well Water

Giardia and Cryptosporidium are the parasites a cyst rating on a filter refers to. Chlorine barely touches Cryptosporidium at the strengths used in drinking water, even with long contact time, the CDC says; Giardia holds out longer than bacteria too, though chlorine gets it with enough time. UV light kills both.

The EPA credits a UV dose of 12 mJ/cm² with killing 999 of every 1,000 Cryptosporidium (11 for Giardia), and a dose of 22 with killing 9,999 of every 10,000 of both. VIQUA rates the VH200 and VH410 at a 30 mJ/cm² dose, above those numbers. That comparison is my arithmetic, not a rating: the EPA table is written for public water plants whose UV reactors are tested and watched by sensors, and what VIQUA claims for its home units is that they are capable of inactivating cryptosporidium and giardia, shown in its own testing. The filters the CDC lists for cysts are certified to NSF/ANSI 53 or 58 for cyst reduction, or have an absolute pore size of 1 micron or smaller; a nominal 1 micron filter may let some through.

When a Well Needs a UV Light

If a lab report shows coliform or E. coli, I recommend a UV light. A caller in July with a positive coliform test asked me whether UV was the answer, and it is: if it's positive for coliform, you should install a UV light.

As I say in the video above, every well needs a UV light, even with a clean test. You can chlorinate the well, but usually it comes back, often about 6 months later. If your report just came back positive, the steps for a positive coliform test (what is safe to use, shocking, retesting) are on their own page, and does your well need a UV light walks through the decision in full.

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A lab test for coliform bacteria

One certified lab test, mailed to you, run by an accredited lab, reports total coliform and E. coli along with the iron, manganese and hardness that decide what goes ahead of the UV light. If you already have a lab report, skip this.

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The Best UV Filtration System for Well Water

For a residential well, the best UV filtration system is one big enough to treat the most water your house uses at once, with a 5 micron sediment filter ahead of it and a controller that tells you when the lamp is due.

We use the VIQUA VH410 on almost every well. It's got high flow rates, and it's got plenty of capacity, whether there's two people or ten people. VIQUA rates it at 18 gallons a minute at its standard 30 mJ/cm² dose, and it is $995. The VIQUA VH200 ($895, 9 gallons a minute) is shorter and fits a tight space. A caller with a one bathroom house asked me whether the VH410 was overkill. Not with bacteria. It's never overkill.

If you are comparing brands, my buyer's guide to whole house UV systems puts the VH410 beside the others, and the Viqua VH200 vs VH410 comparison sets our two side by side.

Why Clean Water Comes First

The lamp can only kill what its light reaches, so the water has to be clear before it gets to the chamber. Sediment and cloudy water throw shadows that bacteria can hide in. Hardness and iron coat the sleeve. As I explained it to a caller in May, the bulb goes inside a crystal tube, and it gets hot inside there, and it bakes the dissolved hardness onto the crystal tube and cuts down on the intensity of the bulb.

Above 7 grains of hardness, VIQUA says the water should be softened, and I tell people the same: skip the softener and you could get bacterial bleed through. These are VIQUA's limits for the water going into the chamber:

Lab report in hand

Text me your test results

Send a photo of the report and I will tell you what, if anything, has to go ahead of the UV light.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

Where the UV Light Goes

The UV light goes after the sediment filter and any iron filter, softener or carbon tank, on the cold line before it branches off to the house. In order, from the well:

1. The well pressure tank. Everything below comes after it.
2. A 5 micron sediment filter. VIQUA requires one ahead of the UV light.
3. An iron filter, if iron or manganese is over the limit.
4. A water softener, if hardness is over 7 grains.
5. A carbon tank, if you have one.
6. The UV light. Then the water goes to the house.

That is the order I give on the phone: pressure tank to the iron filter, water softener, then UV last, because you want the hardness, hard water and iron completely out before it goes through the UV. An acid neutralizer's place depends on the rest of your water, and I set it from your test. For iron bacteria, our customers use the Katalox Light iron filter with air injection and a UV light after it (more in the iron bacteria guide). The full order for every piece of equipment is in the correct order for well water treatment systems.

Sizing a UV System for Your Home

A UV light is sized by the flow it can treat at a given dose, not by the number of bathrooms. Faster water spends less time under the lamp and gets a smaller dose, so VIQUA rates each unit at three doses. The 30 mJ/cm² standard dose is the one the product names use; the stronger dose is 40.

Viqua VH200 vs. VH410

Both units have the same pipe connections, so the choice is not about your pipe size. I use the VH410 because it has the higher flow rate, so you won't have a pressure drop; the VH200 is the one for a spot where the longer chamber will not fit.

Installation Basics

We recommend a licensed plumber for the install, and I support your plumber by phone at 800-460-5810. We don't do installations; we ship the UV light to you and a local plumber puts it in. For the UV light alone, it shouldn't take a plumber, a decent plumber, any more than an hour to put it in. A train with a sediment filter, a couple of tanks and the UV light is more like 3 to 4 hours.

What ships in the box

The chamber comes with the quartz sleeve already inside it. The lamp ships in its own cardboard tube in the box and slides into the sleeve at install; hold it by the ceramic ends, never the glass. A caller who thought his lamp was missing found it wedged in the cardboard in a small tube. The sediment filter ahead of it is a separate product.

What your plumber needs to know

Annual Maintenance

Change the lamp once a year, every 12 months, on the date rather than when it burns out. VIQUA rates the lamp at about 9,000 hours, a year of running around the clock (every two years in a home used only part of the year). The controller counts down from 365 days; at zero it shows A3 and chirps, and you can hold the reset button to put the alarm off a week at a time, up to 4 times, while the new lamp ships.

Changing the lamp

Turn the power off, shut off the water and open a faucet after the UV light to release the pressure; VIQUA says not to use water during a lamp change. Undo the lamp connector, slide the old lamp out of the sleeve, and slide the new one in by its ceramic ends. Then reset the timer: hold the reset button, plug the controller back in, and let go when 365 shows. A caller whose new controller kept beeping had skipped that step. VIQUA also says to run its bleach procedure on the plumbing after a lamp change.

Cleaning the glass sleeve

Minerals slowly film the sleeve, and the film cuts the light reaching the water. VIQUA's manual gives no set schedule: clean it when it films over. That means shutting the water off, draining the chamber and taking the sleeve out. Wipe it with vinegar, CLR or another mild acid, rinse it, and put it back. If it will not come clean, or it is scratched or cracked, replace it ($145 for the VH410, $110 for the VH200). Go easy on the retaining nuts: a caller this spring cracked his sleeve undoing the bottom seal during a bulb change and had to order a new one. If the chamber drips afterward, VIQUA says the O-ring seal is the most likely cause; wipe the O-rings and threads clean and do not over-tighten.

Cost of Ownership

The lamp and the electricity are the yearly running costs of a UV light. A sleeve is extra only if it will not come clean. The first lamp comes in the box, so lamps start in year 2. Power is my arithmetic: VIQUA's wattage running all year at 18.31 cents a kilowatt-hour, the U.S. average the EIA reported for July 2026.

The plumber is a one-time cost on top of that. The 5 micron cartridge in the sediment filter ahead of the UV is its own small cost: $55 for the 20 inch Big Blue cartridge, about every 4 to 6 months on a typical well. The UV water treatment system cost page goes through the numbers in more detail.

UV vs. Other Disinfection Methods

For a home on a well, a UV light treats every faucet for bacteria with no chemicals to add and one lamp change a year.

For the two side by side, see UV disinfection vs chlorination.

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