What Type of Iron Is in My Well Water? (Ferrous vs Ferric vs Bacteria)

Ferrous iron is iron dissolved in your well water, so the water comes out of the tap clear and turns orange after it sits. Ferric iron has already turned to rust before it reaches you, so the water is reddish to orange the moment it leaves the faucet. People ask me all the time which one they have, and the answer starts with a glass of water. Iron bacteria are a third thing: living organisms that leave slime in the toilet tank. Tap the one that looks like yours.

Which one looks like yours? Tap it.

Orange the moment it pours Clear, then stains the toilet Rusty at first, then clear Slime in the toilet tank

The three types of iron in well water

Iron dissolves into groundwater as it passes through rock and soil. By the time it reaches your faucet, it can take one of three forms. Ferrous iron is still dissolved, ferric iron has already turned to rust, and iron bacteria are living organisms that feed on the iron. Which one you have decides what you see at the tap and in the toilet.

Ferrous iron (clear-water iron)

Ferrous iron is iron in solution. The water looks clear coming out of the faucet, then it sits in the toilet tank or a glass, meets the air, oxidizes and starts to stain. If you pour a glass of your well water and an hour or two later it turns orange, that is clear-water iron. At a low level it can take a day or 2. Ferrous iron passes right through basic sediment filters because it is dissolved: a cartridge catches particles and dirt, not iron that is still in the water.

Ferric iron (red-water iron)

Ferric iron has already turned to rust in the aquifer that feeds your well, so the water comes out of the faucet with a reddish to orange tint and stays that color as it runs. People ask me, "I just moved into a house with a well, and the kitchen faucet runs orange. What is that?" That is red-water iron. A spin-down or cartridge filter from the hardware store will not fix red-water iron; the air-injection Katalox Light filter is rated to remove up to 30 ppm of either red-water or clear-water iron.

Iron bacteria

Iron bacteria are living organisms that feed on the iron in the water and leave deposits of iron and a red or brown slime, which sticks to well pipes, pumps and plumbing fixtures. They are not known to cause disease, but the Minnesota Department of Health says they can create conditions where disease-causing organisms grow, and they can make an iron problem much worse. How to tell their slime from plain iron is under Is the toilet tank slime iron bacteria?

How to tell which iron you have

You can tell ferrous from ferric iron by looking at a glass of your water. These four checks take two clear glasses, a day of waiting and a look in the toilet.

1. Fill a clear glass from the cold tap

   Look at it right away. If it is reddish to orange the moment it fills, that is red-water (ferric) iron. If the water is clear, set the glass aside for step 3.

2. Fill a second glass after the tap runs

   Red-water iron stays the same color as the water keeps running. If only the first glass is rusty and the water then runs clear, that water sat in the pipes; it is not red-water iron. Rusty well water covers the pipes versus the well.

3. Let the clear glass sit for a day

   Check it in an hour or two and again the next day. Turning orange or brown means clear-water (ferrous) iron. How fast depends on how much iron there is; at a low level it can take a day or 2, and sometimes the water stays clear even with iron in it, which only a lab test shows.

4. Look in the toilet you use most

   Clear-water iron oxidizes in the bowl and stains it a reddish orange. Clumps floating in the tank with a bad smell point to iron bacteria instead; Is the toilet tank slime iron bacteria? sorts that out.

In this short video I go through the two kinds of iron and how to tell them apart at the faucet.

Is the toilet tank slime iron bacteria?

Real iron bacteria usually show up as clumps floating in the toilet tank and a bad, swampy smell; orange slime on its own is often iron buildup or fine red clay. A caller in Virginia had orange slime in the tank and small hardware-store filters that clogged so fast the house was down to about one shower a day. From what he described, it sounded like fine clay carrying iron, not bacteria.

The Minnesota Department of Health lists the other signs: a smell described as swampy, oily or petroleum, cucumber, sewage or musty, often stronger after the water has sat unused; a rainbow, oil-like sheen on standing water; and sticky rusty, yellow, brown or grey slime. A lab test confirms it, so when the signs are mixed, I tell people to get the water tested before buying anything.

Treating iron bacteria, including why shocking the well with bleach is only a temporary fix, is in my iron bacteria guide.

Ferrous vs ferric vs iron bacteria

This table is the short version of everything above, plus what each common filter does with each kind.

What the iron number on my test means

Your lab report shows one iron number; it does not say how much is ferrous and how much is ferric. The standard panels my customers send in report a single iron result, so the glass test tells you the type and the number tells you how much.

The EPA's secondary standard for iron is 0.3 mg/L, a non-enforceable guideline for rusty color, sediment, metallic taste and reddish or orange staining. About one test in six that my customers send in is over it (89 of 562). The number is what sizes the filter: when someone calls me with iron, I ask how much iron and how many people live in the house. Reading the iron line, including a "<" result, is in how to test for iron in well water.

Already have a lab report? Skip this. No number yet: certified lab test, $199

One lab test gives you the numbers

One certified lab test, mailed to you, run by an accredited lab, gives you the iron, pH, hardness and manganese numbers that size the filter. If you already have a lab report, skip this.

Get the certified well water test

$199 for 53 contaminants.

Does the type of iron change the fix?

For ferrous and ferric iron the fix is the same: an air-injection filter with Katalox Light, rated for up to 30 ppm of either one. A caller in Virginia had 7 ppm, 4 of it ferric and 3 ferrous, with a pH of 6 and 2 grains of hardness. Both kinds at once is fine: from what we've found and tested, Katalox Light takes out both types without any issue. What changes the setup is the pH and whether bacteria are in the well.

The pH comes first. Katalox Light needs the pH around 8 to remove iron properly. If the water is acidic, the filter works for a short time and then iron starts bleeding through, so at a pH like 5.5 or 6 a backwashing acid neutralizer goes in front of it to bring the pH up. In the tests my customers send in that are over 0.3 mg/L iron, about one in four has a pH below 7 (23 of 89).

Iron bacteria need more than the filter. Shocking the well with bleach knocks the bacteria back, but it is usually a temporary fix and they return. When they do, my customers have found the Katalox Light filter also removes iron bacteria when a UV light goes after it. The full plan is in the iron bacteria guide.

The media lasts 6 to 8 years. Depending on how much water you use, you replace the Katalox Light about every 6 to 8 years, with no yearly maintenance in between. Sizes include 1.5 cubic foot ($2,495), 2.0 cubic foot ($2,695) and 2.5 cubic foot ($2,895); every size and price is on our iron filter page.

Did the glass test and still not sure?

Text Aidan what you see

Tell him what the glass did, what is in the toilet tank, and your iron and pH numbers if you have them. He will tell you which iron it is and what fixes it.

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

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

What buyers with iron wrote

These are verified purchases, newest first. Each buyer named the kind of iron or the color they were fighting.

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