Quick Guide to Iron: What You Need to Know

Iron is one of the most common elements found in groundwater, and if your tap water leaves orange stains, tastes metallic, or looks a little rusty, iron could be the reason. While it’s not usually a health risk, iron can cause plenty of household headaches (and plumbing problems). 

In this contaminant quick guide, we’ll break down the different forms of iron, their sources, and how to test and treat your water to make sure iron isn’t a problem.

Table of Contents:

• What Is Iron?
• How Does Iron Get Into Drinking Water?
• Is Iron in Water Harmful to Your Health?
• What Level of Iron is Safe?
• How Do You Know If Iron Is in Your Water?
• Testing for Iron in Drinking Water
• What You Can Do About Iron in Drinking Water
• What’s the Takeaway?

What Is Iron?

Iron (Fe) is a naturally occurring metal found throughout the Earth’s crust. It’s essential for human health — our bodies need small amounts of iron to transport oxygen — but too much of it in drinking water can create aesthetic and maintenance issues.

In water, iron exists mainly in two forms: ferrous and ferric.

• Ferrous Iron (Fe²⁺): Also known as “clear water iron”, this dissolved form is invisible when freshly drawn but oxidizes over time. That’s when clear water turns reddish-orange and leaves stains on sinks or laundry.
  
  
• Ferric Iron (Fe³⁺): Often called “red water iron”, this form has already oxidized into tiny rust-like particles, giving water a cloudy, rusty appearance straight from the tap.

Iron can switch between these forms depending on water chemistry — especially pH and oxygen levels.

How Does Iron Get into Drinking Water?

Iron commonly seeps into private wells and municipal systems as groundwater moves through iron-rich rock or soil. It can also leach from corroding pipes, especially in older plumbing systems or water mains.

Municipal water systems typically use a combination of treatment technologies, including oxidation and filtration, to try to remove iron from the water. Still, some city water supplies retain low levels of iron or end up with iron entering the water in the distribution system (via pipe corrosion).

Is Iron in Your Water Harmful to Your Health?

For most people, iron in drinking water is not a health concern. The Environmental Protection Agency (EPA) classifies iron as a secondary contaminant, meaning its main effects are aesthetic (causing color, flavor, or odor changes).[1]

Relatively low concentrations of iron can affect the taste and color of water and cause staining of plumbing fixtures and laundry, as low as 0.05 PPM (parts per million).[2] The presence of iron can also promote the growth of iron bacteria, which create slimy, orange-brown films that can clog plumbing and reduce water pressure.

Ultimate Tap Water Color Guide: Causes, Meanings & Fixes

What Level of Iron Is Safe?

The EPA recommends that iron levels in drinking water stay below 0.3 PPM, while other sources say issues can start at levels as low as 0.05 PPM.[2] Above 0.3 PPM, you’re likely to notice staining, discoloration, or metallic taste. Lower levels can cause gradual staining over time, so if you’re seeing rust marks or orange buildup, it’s worth testing your water.

The presence of iron can stimulate iron bacteria growth as well–these bacteria derive energy from converting ferrous iron to ferric iron and produce problematic slime.

How Can You Tell if Iron Is in Your Water?

Iron can leave some pretty clear indicators in your water and surrounding faucets and fixtures. These include:

• Reddish or brown stains on sinks, tubs, or toilets
• Metallic taste or odor in tap water
• Cloudy or rusty appearance (including after standing)
• Orange or black slime around fixtures (a sign of iron bacteria)

Helpful Hint: If your water appears clear but leaves stains after sitting, you’re likely dealing with ferrous iron. If it’s reddish right out of the tap, it’s probably ferric iron.

If you have any doubts, it’s always worth having your water tested.

How to Test Your Water for Iron

The best way to know how much — and, in particular, what kind — of iron is in your water is to test for it. There are a number of tests available. We recommend:

Private Well Owners

Public Utility Customers

These specialized tests allow you to explore iron levels in varying ways, via water discoloration, suspicion of iron bacteria growth, or speciation. 

Specialized

What Can You Do About Iron in Your Water?

Treatment depends on which type of iron you’re dealing with:

• For ferrous iron (clear water): Consider adding an oxidation step (such as aeration or chemical oxidants like chlorine or ozone), followed by filtration.
• For ferric iron (red water): Filtration alone (using a sediment or manganese greensand filter) is usually enough.

If iron bacteria are present in your well, shock chlorination or continuous disinfection may be needed. Iron bacteria are notoriously difficult to get rid of entirely, especially in cases of severe infestations.

Shock Chlorination Quick Guide: Disinfecting Your Well Water

Tap Score’s award-winning reports, included with every test, include unbiased treatment recommendations tailored to your specific water report.