Quick Answer: For ongoing bacteria or coliform in a private well, the whole-house answer is a UV system with clean water feeding it. The VIQUA VH410 is our pick for most homes. Viqua rates it at 14 GPM at the 40 mJ/cm² dose used by NSF and EPA, and it's listed under NSF/ANSI 55. If you'd rather buy the pre-filters and UV as one unit, the Viqua VH200-F12 has sediment and carbon built in. Before buying either, shock-chlorinate and retest. A single positive result often has a fixable cause that UV would only cover up.
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Your well test came back positive for total coliform, or worse, E. coli. The first move isn't to buy anything. Boil or buy drinking water, then figure out why the well is positive. A cracked well cap, a missing seal, a low spot where surface water pools after rain, or recent pump work can each cause a one-off positive. Fix the cause, shock-chlorinate the well, and retest. Our guide on shock chlorination with a softener in the system covers the steps and how to protect your resin.
Buy a UV system when the problem keeps coming back, or when the well is simply vulnerable: shallow, dug, in karst, or downhill from a septic field. The EPA's private well guidance is a good primer on why private wells are the owner's responsibility to test and treat.
In this guide
UV only works on water it can see through
UV doesn't filter anything out. It hits bacteria with ultraviolet light as water passes a lamp inside a quartz sleeve. Anything that shades the bacteria or coats the sleeve cuts the dose. Viqua's spec sheets for its VH-series systems list the water quality limits:
- Hardness under 7 gpg (120 mg/L). Harder water scales the sleeve.
- Iron under 0.3 mg/L. Iron stains the sleeve brown.
- Tannins under 0.1 mg/L. Tannins absorb UV.
On a lot of wells, those limits mean the UV lamp is the last piece of equipment, not the first. A typical order is sediment filter, then iron treatment if needed, then a softener if hardness is above 7 gpg, then carbon, then UV at the end. Our well water treatment train order guide lays out the logic.
A side note on "iron bacteria." That slimy orange growth in toilet tanks is a different problem from a coliform result, and it calls for a different fix. See iron bacteria in well water before you assume a UV lamp will solve it.
The dose number on the box is not the one to size by
UV makers publish flow ratings at two doses. 30 mJ/cm² is Viqua's own standard. 40 mJ/cm² is the dose Viqua labels "NSF/EPA." The same unit gets a lower flow rating at the higher dose. Size by the 40 mJ number:
| System | Flow @ 30 mJ/cm² | Flow @ 40 mJ/cm² | Ports |
|---|---|---|---|
| VIQUA VH410 | 18 GPM | 14 GPM | 3/4"–1" MNPT combo |
| Viqua VH200-F12 | 9 GPM (VH200 chamber) | 7 GPM | Check listing |
| Viqua VH150 | 5 GPM (dose not published) | Not published | 3/4" x 1" NPT |
| iSpring UVF55FS | 12 GPM (dose not published) | Not published | 1" MNPT |
How much flow do you need? Here's a real example: a 3-bath house where two showers (about 2 gpm each), a dishwasher and a toilet refill overlap can hit 7–8 gpm. The VH200-F12 is at its 40 mJ limit there. The VH410 has room to spare. Also check your well pump's output. A UV rated above what your pump can deliver doesn't hurt anything, but there's no reason to pay for it.
The five systems
VIQUA VH410: the one we'd install on most wells
At 14 GPM at 40 mJ/cm², the VH410 covers almost any single-family house. The retailer listing we checked says it's certified to NSF/ANSI 55 (Class B) and CSA B483.1 through NSF, plus UL for electrical safety. Class A and Class B are different ratings under that standard. If you're treating water with confirmed contamination, ask Viqua which model and class fits your case before you buy.
Practical details: a 9,000-hour lamp you replace every 12 months, a quartz sleeve to replace every 24 months, and a 60 W draw. A controller counts down lamp life with an audible reminder and alarms if the lamp fails. A seller of the VH410-F22 package lists a 10-year warranty on the chamber, 3 years on electrical and 1 year on the lamp.
Downside: it's just the UV. You still need pre-filtration and, on hard water, a softener ahead of it.
Viqua VH200-F12: sediment, carbon and UV on one rack
This is the "I don't want to design a system" pick. A sediment filter and a carbon block filter mount on the same rack as a VH200 UV chamber, so the lamp always gets pre-filtered water. It ships with the S200RL-HO lamp, QS-001 quartz sleeve and both filters. Viqua rates it at 9 GPM, and the VH200 chamber drops to about 7 GPM at the 40 mJ/cm² dose. The lamp is rated for a year or 9,000 hours, a Safety-Loc connector cuts power before you can pull the lamp, and the stainless chamber carries a 10-year warranty.
Who it fits: a 1–3 bath home on a well with clean, fairly soft water and an intermittent bacteria problem.
Who should skip it: households that often pull more than about 7 gpm, and anyone whose water is over 7 gpg hard or has iron above 0.3 mg/L. The built-in filters don't fix either of those, so you'd still need a softener or iron filter first.
Viqua VH150: right-sized for small homes and cabins
Same stainless VH family as the VH410, in a much smaller size. Viqua lists it as a 5 GPM point-of-entry unit for small homes (1–3 bathrooms), with a high-output lamp you replace annually or every 9,000 hours, a timer that counts down the days to the next lamp change, 3/4" x 1" NPT connections and a 110–240V supply. The listing doesn't publish a 40 mJ/cm² flow, so treat 5 GPM as the ceiling, not the comfortable number. Plan on the same water limits as the rest of the family: hardness under 7 gpg, iron under 0.3 mg/L, tannins under 0.1 mg/L.
For a cabin, a 1–2 bath house or a seasonal place, it's all you need. It's UV only, so add a sediment filter ahead of it. Once the house regularly runs two showers at once, step up to the VH410.
iSpring WGB32B-KS + UVF55FS: filter and UV in one box
This bundle pairs iSpring's three-stage sediment/KDF/carbon system with its UVF55FS UV unit. That's a complete pre-filter-then-UV setup in one order. The KS filter set also reduces hydrogen sulfide and chlorine, which helps right after a shock chlorination.
Who it fits: a well owner who wants everything from one brand and one order, and whose water is already reasonably soft and low in iron.
Downside: iSpring doesn't publish a UV dose for the UVF55FS. You're trusting a 12 GPM rating without knowing the mJ/cm² behind it, so we rank it below the Viqua units.
iSpring UVF55FS: UV only, for an existing filter rack
If you already have sediment and carbon filtration, this adds UV for less hardware. The spec sheet lists 12 GPM, 1-inch MNPT ports, a 55 W lamp rated for up to 9,000 hours (replace yearly), and a 37.5-inch 304 stainless chamber. It's rated for 4–85 psi and water up to 100°F. A flow sensor turns the lamp on and off with water flow. Clean the quartz sleeve every 6–12 months.
What owners report: some reviewers say the flow switch has straight threads rather than NPT and needs a gasket. Others say a ballast failed and iSpring replaced it. And again, no published dose.
Two wells, two different answers
A 1970s dug well behind a farmhouse, coliform positive twice in two years. It's shallow, with a buried well cap, and the field above it gets manure. First, raise the casing and seal the cap. Then shock-chlorinate and retest. Because it's vulnerable by design, this well gets permanent UV anyway. The water tests 14 gpg hard with 0.6 mg/L iron, both over Viqua's limits, so the order is sediment, then an iron filter, then a softener, then the VH410 at the end. Skipping the softener here would leave the sleeve scaled within months.
A newer drilled well, one positive test right after a pump replacement. That's very likely contamination from the pump work. Shock, flush and retest. If the follow-up tests come back clean, you may not need UV at all. Keep testing on a regular schedule. If you'd still sleep better with UV, a VH150 or VH200-F12 sized to the house is plenty.
Questions worth asking before you buy
Does UV work during a power outage? No. The lamp needs power to disinfect, and water keeps flowing from the pressure tank after the power goes out. If your area loses power often, plan for it: bottled drinking water during outages, or a shutoff that stops flow when the UV loses power.
Can the UV go before the softener? Only if your water is already under the hardness and iron limits. Otherwise scale and iron coat the sleeve, and the dose drops while the lamp keeps glowing.
Do I still need to shock the well if I install UV? Yes, if you've had a positive test. UV treats water passing the lamp. It doesn't clean the well, the pressure tank or the pipes after it.
Is a carbon filter enough? No. Carbon improves taste and catches some chemicals. It isn't a disinfection step.
Keeping a UV system honest
A UV system that's on but not working looks exactly like one that is working. Three habits keep it working:
- Change the lamp every 12 months, even if it still glows. Both Viqua and iSpring call for yearly replacement. Our UV lamp and sleeve replacement guide covers the swap.
- Clean the sleeve on the schedule your model calls for, and more often on hard or iron-bearing water.
- Retest for bacteria after install and then on a regular schedule. Our article on testing well water for coliform explains sampling so you don't get a false positive from the faucet.
UV adds nothing to the water that stays in your pipes. So after plumbing work downstream of the lamp, or if the lamp was off for a while, retest rather than assuming the lines are clean.