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Iron Bacteria in Well Water: How to Spot It and Get Rid of It for Good
If your toilet tank has a reddish-brown slime, your water smells swampy, and orange stains come back no matter how often you clean, the problem may not be iron alone. It may be iron bacteria: harmless-to-health but extremely persistent organisms that live in wells and plumbing and feed on dissolved iron and manganese. Here's how to tell iron bacteria from ordinary iron, how to confirm it, and what actually gets rid of it, because the usual iron filter won't.
What iron bacteria are
Iron bacteria are naturally occurring microorganisms (the common ones are Gallionella and Leptothrix) that get their energy by oxidizing dissolved iron and manganese. As they do, they build up a slimy coating of bacteria and rust-colored deposits on everything they touch: the well casing, the pump, the pressure tank, pipes, and toilet tanks. They usually get into a well during drilling or pump work and, once established, are very hard to remove completely.
They are not a known health hazard. The problems are practical: slime that clogs pumps, screens and filter media; staining that's worse than iron alone; unpleasant tastes and odors; and a slime layer that can shelter other bacteria, including the sulfur-reducing kind that cause a rotten-egg smell.
Iron bacteria or just iron? How to tell
| Sign | Ordinary dissolved iron | Iron bacteria |
|---|---|---|
| Toilet tank | Orange stain or sediment | Slimy, gelatinous red-brown coating you can wipe off in strands |
| Surface of standing water | Nothing unusual | Rainbow or oily-looking sheen that breaks into flakes when you touch it |
| Smell | Metallic, or none | Swampy, musty, cucumber-like or sewage-like; often with a rotten-egg smell too |
| Staining | Orange-brown, builds slowly | Heavier, slimier, comes back fast after cleaning |
| Iron filter or softener | Works as designed | Media fouls with slime; performance drops within months |
The sheen test is the quickest check at home. An oil sheen swirls back together when you poke it; an iron bacteria sheen breaks apart into small flakes and stays broken.
How to confirm it
- Look in the toilet tank first; it's the most reliable visual sign in the house.
- Order a lab test that includes iron, manganese, hydrogen sulfide and pH, and ask about iron-related bacteria specifically. Many county health departments and certified labs offer it, and home "BART" test kits detect iron-related bacteria by culturing a sample over several days.
- Ask your well driller or pump installer what they saw if the pump has been pulled recently. Heavy slime on the pump and drop pipe confirms it.
How to get rid of iron bacteria
Step 1: Shock chlorinate the well
The first move is always a strong one-time dose of chlorine through the well and plumbing to kill the bacteria and break down the slime. Our step-by-step guide on how to shock a well covers how much bleach to use for your well, how to circulate it, and how to flush safely. For heavy infestations a well contractor may also brush or jet the casing first, because chlorine can't reach bacteria protected under thick slime.
Step 2: Watch for it coming back
Shocking often works for weeks or months, and sometimes for good. But iron bacteria live in the formation around the well as well as inside it, so in many wells they return. If the slime and smell are back within a few months, repeated shocking is a treadmill.
Step 3: The permanent fix, continuous chlorination
For iron bacteria that keep returning, the reliable long-term solution is a well water chlorination system: a metering pump injects a small dose of chlorine whenever water flows, a retention tank gives it time to kill the bacteria and oxidize the iron, and a backwashing carbon filter removes the chlorine and the precipitate before the water reaches your taps. It handles iron bacteria, heavy iron and sulfur in one train.
| Approach | What it does | Best for |
|---|---|---|
| Shock chlorination | Kills bacteria in the well and plumbing once | First treatment; new infestations; after pump work |
| Continuous chlorination + retention tank + carbon | Keeps a chlorine residual so bacteria can't re-establish; oxidizes iron and sulfur | Iron bacteria that return; heavy iron; iron plus sulfur |
| Air-injection or Greensand iron filter alone | Removes dissolved iron | Iron without bacteria; on bacteria-infested wells the media fouls with slime |
The complete 15 GPD chlorination system with Stenner pump includes the pump, solution tank, flow switch, 120-gallon retention tank and carbon filter. Sizing the retention tank to your well's flow is covered on the chlorination collection page.
Quick answers
Are iron bacteria harmful? They aren't known to cause illness, but the slime they create can harbor other bacteria, clog equipment and make water taste and smell bad. If you see the signs, test for coliform bacteria too.
Will a water softener get rid of iron bacteria? No. The slime fouls softener resin. Treat the bacteria first; then the softener can handle hardness.
Why does my iron filter keep failing? If the media is coated in slime within months, iron bacteria are the likely cause. Shock the well and consider chlorination ahead of the filter.
Can I just keep shocking the well? You can, but if you're shocking more than a couple of times a year, a chlorination system is cheaper and far less work over time.
Not sure what's in your well? Send us your water test or call 800-374-2143. Related: iron filters · sulfur filters · why does my water smell like rotten eggs?
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