Iron bacteria in well water
Iron bacteria are the one well-water problem that is genuinely two problems at once. Organisms that oxidise dissolved iron and deposit it as rust-coloured slime are living, so they regrow — while the iron deposits they leave behind are mineral, so they foul surfaces and clog lines. Neither treatment alone settles it: oxidation and filtration remove the iron, and ultraviolet treatment at the end of the chain stops the organisms from passing to the tap. The unit's feed-water limit of iron below 0.3 ppm is the reason the two stages cannot be swapped.
Slime, staining and a metallic smell
Why this is not a single-stage fix — see the order.
Can UV be fitted first?
No — and the reason is in the feed-water table, see the limits.
UV is a disinfection component. It has no media and no membrane, so it is not a removal stage — and it is not a stand-alone purifier. Everything dissolved is decided upstream of it.
What iron bacteria are, and why they are not a single organism
"Iron bacteria" is a working name for a group of organisms — among them Gallionella and Leptothrix species — that live by oxidising dissolved ferrous iron into ferric iron and depositing the result around themselves. The deposit is what you see: a rust-coloured, slick, gelatinous material that coats screens, pipes, tanks and fixtures.
They are not a health hazard in the way coliform bacteria are. They are a system hazard: the slime builds up, restricts flow, shelters other organisms, and produces a persistent metallic or swampy taste even after the water has been filtered.
| What you notice | Why it happens |
|---|---|
| Rust-coloured slime on screens, aerators and tank surfaces | Deposited ferric iron bound in an organic matrix the organisms produce |
| Flow falls off over months, then recovers after cleaning | Slime accumulating on screens and inside lines, then being physically removed |
| Metallic, swampy or oily taste and smell | Metabolic by-products in the deposit, released as water passes |
| Staining that returns quickly after cleaning | The organisms are still present — cleaning removes the deposit, not the population |
A deposit can be scrubbed away in an afternoon. If the organisms remain, the deposit returns. That is the difference between cleaning a well and treating one, and it is why a treatment train rather than a maintenance routine is the durable answer.
Oxidise, filter, soften, then disinfect
The order follows from what each stage can do. Iron has to be taken out of solution before it can be filtered, which is what oxidation does. Once the iron is gone, the downstream stages stop being fouled — and only then can an ultraviolet stage be trusted to deliver its dose.
- Air or chemical oxidation. Aeration, or controlled dosing of chlorine or ozone, converts dissolved ferrous iron into ferric iron that will settle or be caught by a filter medium. Oxidation is also what makes the deposit removable at all.
- Filtration. The oxidised iron is caught in a filter medium and backwashed out. This is the stage that physically removes the metal — a UV unit cannot substitute for it.
- Softening, where hardness is also high. Scale on the quartz sleeve reduces UV transmission the same way iron deposits do, so hardness is handled before the lamp, not after it.
- Ultraviolet treatment, last. With iron below 0.3 ppm and turbidity below 1.0 NTU, the sterilizer sits at the point of use and inactivates what remains in the water. It cannot regrow what passes it.
The single sentence to take away: oxidation and filtration remove the problem; UV keeps it from coming back through the tap. Neither one replaces the other, and swapping their order breaks both.
Why a sterilizer cannot go in front of the iron filter
An ultraviolet unit delivers dose through a quartz sleeve. Anything that plates onto that sleeve — iron deposits, scale, biological slime — reduces the light reaching the water. That is the mechanical reason the feed-water limits exist, and it is why the limits are written as warranty conditions rather than as recommendations.
| Maximum iron | < 0.3 ppm |
|---|---|
| Turbidity | < 1.0 NTU |
| Maximum hardness | < 120 ppm |
| pH | 4 – 8 |
| Chlorine concentration | ≤ 1.0 mg/L |
| Feed water pressure | ≥ 14.5 psi and ≤ 60 psi (0.1–0.4 MPa) |
| Inlet water temperature | 32–100 °F (0–37.8 °C) — cold water only |
| Water use | Drinking water supply only — water must be pre-filtered |
The unit does not fail loudly. It keeps running, the indicator keeps reading green, and the water keeps flowing — but the sleeve progressively fouls, and the treatment the unit was specified to deliver stops being delivered. This is the failure mode to watch for on any iron-bearing supply, and it is invisible without inspection.
What the routine actually is on an iron-bearing supply
The indicator light
Blue means powered and standing by, green means the lamp is running, red means a fault. It is the only routine check, and there is no lamp countdown to track.
The quartz sleeve
This is the real maintenance point, and on an iron-bearing supply it is the item that sets the service interval — not the emitter's rated life of 15,000 hours.
The upstream stages
Backwash schedules on the iron filter matter more than usual here: an oxidising filter left too long between backwashes passes iron through to whatever sits downstream of it.
The rated design life of the UVC-LED assembly is 15,000 hours, stated with an output criterion of not less than 60% of initial output. It is a design rating, not a validated service-life claim — and on a point-of-use installation the lamp runs only while water flows, so it is rarely the limiting factor.
Iron bacteria and UV
Will UV treatment kill iron bacteria?
Ultraviolet treatment inactivates micro-organisms in the water passing the lamp, including iron-oxidising bacteria. What it does not do is remove the iron they feed on, or clear the deposit already established on screens, pipes and tank surfaces. Without upstream oxidation and filtration, the organisms simply re-establish.
Is iron bacteria dangerous to drink?
Iron bacteria themselves are not regarded as a health hazard in the way faecal coliform bacteria are. The concern is indirect: the deposit gives other organisms somewhere to live, it fouls treatment stages, and it can make the water unpalatable. A positive bacteriological result alongside iron bacteria is a different matter — that is a pathway problem and should be investigated.
Can I just clean the well instead of installing treatment?
Cleaning removes the visible deposit. If the organisms remain, the deposit returns — which is why wells with this problem tend to be cleaned repeatedly. A treatment train that removes the iron and disinfects at the point of use addresses the cause rather than the symptom.
Why can't the UV unit go in first, before the iron filter?
Because iron deposits and biological slime plate onto the quartz sleeve, and the light has to pass through that sleeve to reach the water. The unit's feed-water limit is iron below 0.3 ppm for exactly this reason. Put in front of the iron filter, the sterilizer keeps running and giving a green light while delivering progressively less treatment.
Does an iron filter remove the bacteria as well?
It removes the iron, and backwashing carries away a good deal of the biological material with it — but filtration is not disinfection. Organisms that pass the filter medium reach the water downstream, and anything established on the wetted surfaces after that stage is outside the filter's reach. That is the gap a UV stage closes.
Describe the deposit, not the colour
Where it appears, how fast it returns and what the test showed are what distinguish an iron problem from an iron-bacteria problem.
- Models: ZXSJ-UVC-1GPM ｜ ZXSJ-UVC-3GPM
- Credential: CE conformity certificate DPCW/01068/06/KA/26 · EPA Establishment No. 105777-CHN-1 (facility registration)
- Feed water: pre-filtered, turbidity < 1.0 NTU, iron < 0.3 ppm, hardness < 120 ppm
- Samples: available for evaluation before a volume commitment
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Sources and scope
4 sources
- Feed-water limits and declared scope of application: SKWEIT® UV Water Sterilizer instruction manual, revision 01.03, and product parameter table. Cited for: iron, turbidity, hardness, pH, chlorine and temperature limits; flow ratings.
- Treatment sequence: the manufacturer's installation documentation. Cited for: placement of the sterilizer after filtration and after any softening stage.
- Rated life: manufacturer's product specification, stated as a design rating with an output criterion of not less than 60% of initial output — not as a validated service-life claim.
- Iron-oxidising bacteria: standard groundwater microbiology. Cited for: the mechanism by which dissolved ferrous iron is oxidised and deposited, and for the fact that the resulting deposit regrows while the organisms remain present.