Iron filter

Short definition

An iron filter removes dissolved iron and manganese from well water before they oxidize and stain fixtures. The modern standard is air-injection oxidation (AIO) — no chemicals, self-regenerating. Older systems use manganese-greensand with periodic regeneration. WA hot zones for iron and manganese: Olympic Peninsula, Skagit, parts of Snohomish, Pierce, Mason, and Kitsap.

What it is

Well water often contains dissolved ferrous iron (Fe²⁺) and sometimes manganese (Mn²⁺). These are invisible while in the well — but the moment the water hits air at a faucet or in laundry, they oxidize to insoluble forms and produce visible staining: red-brown from iron, black from manganese.

The EPA secondary drinking water standards set iron at ≤0.3 mg/L and manganese at ≤0.05 mg/L. Above those, staining and taste become noticeable.

Iron filters work by deliberately oxidizing the iron and manganese inside the filter, where the resulting precipitate is captured by a media bed and backwashed away on a regular cycle.

The three common types:

1. Air-injection oxidation (AIO) — the modern default. The filter pulls in atmospheric air during backwash, holds an air pocket at the top of the tank, and water passes through that air pocket on the way to the media bed. No chemicals, self-regenerating. Removes 8–15 mg/L iron, 1–3 mg/L manganese.
2. Manganese-greensand — traditional. Uses a special greensand media that’s regenerated periodically with potassium permanganate solution. Effective but requires regenerant.
3. Chlorination plus filtration — heavy-duty for high iron levels or wells with iron-bacteria contamination. Adds chlorine ahead of a filter; chlorine oxidizes iron and kills iron bacteria.
4. Pre-aerator plus filter — large-scale option for very high concentrations.

The filter-train ordering rule: sediment → iron filter → softener → carbon → POU RO. Iron filters go before softeners because dissolved iron damages softener resin.

Why it matters to a homeowner

For Olympic Peninsula, Skagit, and other WA private well homes with iron-rich water, an iron filter is often the difference between functional plumbing and brown-stained everything. Iron-stained laundry doesn’t bleach out — bleach oxidizes more iron and makes the stain worse. The fix is at the source.

A typical install: AIO unit handles iron and manganese together. Cost: $1,500–$3,000 installed in 2026. Service: replace media every 5–10 years, depending on usage and iron concentration.

Pre-purchase due diligence on a WA well home should include lab testing for iron and manganese. A reading of 5 mg/L iron in a well-water test means you’re factoring an iron filter into the purchase budget.

When a contractor says you need a “Jet Pump Filter” or “iron breaker,” verify they’re describing AIO or manganese-greensand specifically. Generic “iron filter” sometimes means a sediment filter that won’t actually do anything for dissolved iron.

Common failure modes

• Iron bacteria growth in untreated well — slime layer in filter, accelerated clogging. Chlorination ahead of filter is needed.
• Backwash frequency wrong — media fouls, iron passes through.
• Greensand exhausted — no regenerant available; install fails until refilled with potassium permanganate solution.
• AIO air-vacuum tube clog — no oxidation; iron passes through.
• pH too low — iron stays dissolved; not removed even by filter. pH-adjustment may be needed upstream.

Common variants

• Iron filter (ferrous Fe²⁺ removal via oxidation plus filtration) vs. sediment filter (catches ferric Fe³⁺ already oxidized; particulate trap only).
• Air-injection (no chemicals, self-regenerating) vs. greensand (potassium permanganate regen) vs. chlorine-based (heavy duty).
• Iron filter vs. softener — a softener removes some iron via ion exchange (≤2 mg/L typical); iron filter handles higher levels and manganese.

Washington note

Iron and manganese in WA wells:

• Olympic Peninsula — high prevalence; iron 3–10+ mg/L, manganese 0.5–2+ mg/L common.
• Snohomish, Pierce, Mason, Kitsap — moderate prevalence; varies by aquifer.
• Skagit and Whatcom — iron, manganese, sometimes paired with arsenic and nitrate. Multi-stage treatment common.
• San Juan Islands and Whidbey — saltwater intrusion is the bigger concern; iron less so.

A few specific scenarios:

Olympic Peninsula well home with 5 mg/L iron and 1 mg/L manganese — single AIO unit handles both.

Skagit Valley agricultural well with iron, nitrates, and arsenic — multi-stage filter train: sediment → AIO iron → arsenic filter → softener → carbon → POU RO.

Snohomish PUD-area well with chlorination at the wellhead — simpler iron filter adequate; no AIO required.

Iron-stained laundry as the homeowner’s first symptom — bleach makes it worse; install iron filter, then re-bleach laundry post-install.

For pre-purchase, a well-water lab test costs $50–$200 and is non-negotiable on any WA well property.