How to Remove Iron from Well Water, by Iron Level and pH

Match the method to your lab numbers. Clear-water (ferrous) iron under about 3 to 5 mg/L, with pH near 7 and some hardness, can be removed by a water softener. From about 3 to 10 mg/L, use an oxidizing iron filter such as Birm, manganese greensand, catalytic media or an air-injection system. Above 10 mg/L, or with iron bound to organic matter, inject an oxidant such as chlorine or hydrogen peroxide and filter out the particles. If your pH is low, raise it before any of these.

Every one of these methods has conditions the dealer may not mention: a minimum pH, a dissolved-oxygen requirement, a hydrogen sulfide limit, a backwash flow your well must deliver. Those conditions are why iron filters fail, so they are in the table below.

Step 1: get four numbers

Before choosing anything, get a lab report with:

1. Iron, in mg/L, and whether it is dissolved (clear when drawn) or already oxidized (red when drawn). The EPA’s secondary standard is 0.3 mg/L.
2. pH. Most iron media need 6.7 to 7 or higher.
3. Manganese. The EPA secondary standard is 0.05 mg/L, and several methods handle manganese poorly.
4. Hardness, if a softener is an option.

Add hydrogen sulfide if the water smells, and dissolved oxygen if you are considering catalytic carbon or Birm. Our iron in well water guide explains the four forms of iron and how to tell them apart at the tap.

Method chooser

Water softener (low clear-water iron)

A softener’s resin exchanges dissolved ferrous iron the same way it exchanges calcium and magnesium. Penn State Extension sets the conditions: dissolved iron under 5 mg/L, pH above 6.7, hardness between 3 and 20 grains per gallon, and raw water that has not touched air or chlorine first, since oxidized iron plugs the resin rather than exchanging. Minnesota’s Department of Health (MDH) says manufacturers claim up to 10 mg/L but 2 to 5 mg/L is a more common real limit, and that an air-charged galvanized pressure tank can ruin performance. Alberta Agriculture puts the practical ceiling at 3 mg/L and recommends a resin cleaner, such as one containing sodium hydrosulfite or phosphoric acid, used regularly.

If your iron is low and your water is also hard, this is the cheapest route. Our water softener guide covers sizing; iron adds to the load the softener must handle.

Sequestering with polyphosphate

A metering feeder adds polyphosphate, which keeps dissolved iron from oxidizing and staining. Penn State Extension limits it to dissolved iron under 2 mg/L, notes it does not work on manganese, and points out the iron is hidden, not removed. Too much polyphosphate can cause a slippery feel and, in excess, diarrhea. It is a stopgap for low iron, not a fix.

Birm

Birm is a granular catalytic media that speeds up oxidation of dissolved iron using the oxygen already in the water; it needs no chemical regeneration, only backwashing. Clack, its maker, lists strict conditions: pH of 6.8 or more (8.0 to 9.0 for manganese), dissolved oxygen at least 15 percent of the iron content, no hydrogen sulfide or oil, and organic matter no higher than 4 to 5 ppm. Bed depth runs 24 to 36 inches. If pH is below 6.8, Clack recommends a neutralizer such as calcite ahead of the Birm tank. Penn State Extension adds that its manganese removal is highly variable.

Birm is a poor choice if your water smells of sulfur or is low in dissolved oxygen.

Manganese greensand

Greensand is coated with an oxidizer that converts dissolved iron, manganese and some hydrogen sulfide into particles it then filters out. The coating is replenished with potassium permanganate. The published ceilings differ: Penn State Extension says 3 to 10 mg/L of combined iron and manganese, Alberta Agriculture about 6 mg/L, and MDH 10 to 15 mg/L. Alberta’s conditions are a pH above 7, at least 5 gallons per minute of flow for backwashing a smaller unit, and a backwash of at least 10 minutes and ideally 30 to 40 minutes. Letting regeneration lapse can ruin the media.

Katalox Light (catalytic MnO2 media)

Katalox Light is a zeolite media with a manganese dioxide coating of about 10 percent, made by Watch Water in Germany and certified to NSF/ANSI 61. The manufacturer lists an inlet pH range of 5.8 to 10.5, a minimum bed depth of 29.5 inches (47 inches optimal), and a service rate of 4 to 12 gallons per minute per square foot. It can run on dissolved oxygen alone or with an oxidant feed; the manufacturer recommends hydrogen peroxide for very high contaminant levels. Watch Water states the media does not remove bacteria.

Air injection

A small venturi-type injector installed between the pump and the pressure tank draws air into the water. The oxygen converts dissolved iron to rust particles that the filter bed strains out. Alberta Agriculture reports these systems working well in many homes and notes that vendors claim up to 30 mg/L, but says high iron usually needs extra equipment such as retention tanks and air-release valves, and that cold water, low pH and organically bound iron cause problems.

Alberta’s simple pre-check: shake air into a jar of fresh well water and watch how readily the iron drops out. If it does not, air alone is unlikely to work.

Chlorine or hydrogen peroxide injection

For iron above 10 mg/L of combined iron and manganese, Penn State Extension recommends oxidation followed by filtration. A metering pump injects chlorine (most common), hydrogen peroxide or potassium permanganate; a mixing tank or pipe coil gives it time to react; a filter catches the particles; an activated carbon filter can remove leftover chlorine taste. Alberta Agriculture adds that water pH must be above 7 for chlorination to work and that chlorine feed must be metered carefully. Penn State notes chlorine is not recommended for very high manganese, which needs a very high pH.

This is the most equipment, but it also handles iron bacteria and hydrogen sulfide. If your iron comes with a rotten-egg smell, read sulfur smell in well water before choosing.

Fix low pH first

Almost every method above wants a pH of about 6.7 to 7 or higher. If your water is below the EPA’s 6.5 floor, a calcite or similar neutralizer ahead of the iron filter raises pH and helps the media work. See our acid neutralizer for well water roundup.

Iron bacteria and organic iron

Slime in the toilet tank or a swampy smell means iron bacteria, which will foul any filter. Alberta Agriculture recommends shock chlorinating before selecting equipment, and again in spring and fall. MDH notes that organic iron and tannins can block oxidation, so softeners, aeration and iron filters may not work; MDH lists chemical oxidation as a possible option there. Distillation and reverse osmosis remove any form of iron, but MDH warns that high iron plugs them quickly.

Check that your well can backwash the filter

Every backwashing filter needs a burst of flow, and regenerating equipment generally needs at least 4.4 gallons per minute, according to Alberta Agriculture. A low-yield well or an undersized pump may not deliver it, and an under-backwashed bed clogs. For low-capacity wells, Alberta describes an alternative: spray the water into a storage cistern to oxidize the iron, let particles settle, then repump through a sediment filter.

Once your numbers point to a method, our iron filter for well water roundup compares systems built on each media.