UV disinfection removes nothing

What is uv water sterilization?

A UV system passes water through a chamber past an ultraviolet lamp, which inactivates microorganisms so they cannot reproduce. It adds no chemicals, changes no taste, and - the point most often missed - removes absolutely nothing from the water. Hardness, lead, iron, chlorine taste and anything else dissolved pass straight through unchanged. UV is one job, done well, at the very end of a treatment train that has already made the water clear enough for light to reach through it.

Signs you need uv water sterilization

• A certified lab result came back positive for bacteria on a private well and your health department has advised treatment
• You are on a well, a spring or a private supply with no disinfection of any kind in place
• Surface water reaches your well after heavy rain, and testing during those events reflects it
• You have shock chlorinated the well repeatedly and the microbiological result keeps returning
• You are on a seasonal or holiday property where the plumbing sits unused for long periods
• An existing UV unit is in place but nobody knows when the lamp was last changed
• You want the last stage of a well treatment train specified properly rather than added as an afterthought

Seeing something not on this list? Browse water treatment problems by symptom →

How uv water sterilization actually works

1. 1

   Establish that you have a microbiological problem, from a lab

   UV addresses organisms. It is the wrong purchase for any other complaint, and the finding that justifies it comes from a certified laboratory and an interpretation from your health department. On a well, this is also the moment to rule out the cap and seal as the entry route.

   Watch forA UV system sold as general "purification" or as an upgrade to a filtration package. If there is no microbiological finding behind it, ask what it is there for.

2. 2

   Fix the clarity problem before the lamp goes in

   UV works by light reaching the organisms. Suspended sediment, turbidity, iron, manganese and tannins all absorb or scatter that light, and organisms can shelter in the shadow of a particle. So sediment filtration, and iron or manganese removal where present, must come first - not as a nicety but as a condition of the UV working at all.

   Watch forA UV unit installed on visibly cloudy or iron-bearing water. It will run, the lamp will glow, the indicator will be green, and the disinfection will be compromised in a way nothing on the unit reports. See iron and sulphur removal for the stage that has to come first.

3. 3

   Place it last in the train, as close to the house as sensible

   Everything that cleans the water goes upstream; the lamp goes at the end. Because there is no residual disinfectant, any pipework, tank or equipment downstream of the lamp is unprotected - anything living in there is downstream of your only barrier.

   Watch forA lamp installed ahead of a storage tank or a softener. Both then sit unprotected on the treated side, and both are places where an organism could establish itself with nothing to stop it.

4. 4

   Size the chamber to your peak flow

   The organisms have to spend enough time in the chamber for the exposure to be effective, so flow rate is the sizing input. Two showers plus an appliance at once is what it must handle, not average daily use.

   Watch forSizing on household size rather than simultaneous demand. Over-run a UV chamber and water passes with less exposure than it needs, silently - there is no symptom and no alarm.

5. 5

   Commission it, and disinfect the plumbing behind it once

   Installing a lamp does nothing about organisms already established in the pipework and fittings downstream of it. Standard practice on a well is to shock chlorinate and flush the whole system, and only then rely on the UV to keep what follows clean.

   Watch forGoing straight to UV after a positive result without disinfecting the existing plumbing. The lamp treats what passes it; it has no effect on what is already living behind it.

6. 6

   Replace the lamp annually and clean the sleeve

   UV lamps lose output long before they stop lighting up. Manufacturers specify replacement on a schedule - commonly annually - and it is not negotiable. The quartz sleeve around the lamp also fouls, particularly on hard or iron-bearing water, and a filmed sleeve blocks the light from a perfectly good lamp.

   Watch forAssuming a glowing lamp is a working lamp. This is the defining maintenance failure of UV systems: the visual cue tells you the electricity is on, not that the output is adequate. Write the change date on the housing.

7. 7

   Plan for power failures

   No power, no disinfection - but water still flows if the house has pressure. Better installations include a solenoid valve that shuts flow when the lamp is not operating, and a lamp-failure alarm. On a well the pump usually stops with the power anyway, but a pressure tank can deliver a good deal of untreated water first.

   Watch forNo alarm and no shut-off valve. Both are inexpensive at install and they are the difference between a system that fails safely and one that fails silently.

What does uv water sterilization cost?

A residential UV system is typically among the cheaper treatment stages to buy - commonly a few hundred to around a thousand dollars installed, more with a solenoid shut-off, alarm and the sediment pre-filtration it requires. The recurring cost is an annual lamp, periodic sleeve replacement and pre-filter cartridges. Budget for those, not just the unit.

See the full uv water sterilization cost guide - by material, size and region →

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