Iron Bacteria in Well Water: How to Confirm Them and Keep Them in Check

What iron bacteria are, and why wells get them

Iron bacteria are organisms that feed on iron and leave behind rust-coloured slime. Alberta Agriculture lists what they need: 0.5 to 4 mg/L of dissolved oxygen, as little as 0.01 mg/L of iron, and water at 5 to 15 °C. Its conclusion: water wells “will almost always produce these conditions”¹. They often get in during drilling, repairs or pump work, which is why Penn State says prevention beats treatment².

They are not a health risk^2,3. The damage is to the well and the house: clogged screens and pipes, lower well yield, corrosion, and conditions where sulfur bacteria and coliforms can grow^1,4. A well that is used only now and then is more prone to the problem⁴.

How to tell

Iron bacteria · three checks

Check	How	Points to iron bacteria
Toilet tank	Lift the lid of a tank without a disinfectant tablet4,5	Slimy residue at the waterline, an oily sheen on the water4
Jar test	Fill a clear jar with water that sat unused for hours, leave it 24 hours5	Fluffy, rust-coloured strands or clumps; a thin flour-like layer is plain iron5
Lab test	A sample from the tap near the pressure tank, early morning4	Results take 2 to 3 weeks in Wisconsin4; few labs offer it5

The University of Georgia notes that iron bacteria tests are seldom needed: confirmation is usually visual⁵. A rotten egg smell points to sulfur bacteria instead⁵; see our sulfur smell guide.

Treatment: a stronger, longer shock

Shock chlorination is the standard first step. For iron bacteria, the sources go further than a routine shock:

• Dose. Minnesota says close to 200 ppm but never more, because a stronger solution makes disinfection less effective³. Alberta’s table also gives 200 ppm and warns that more chlorine is not better¹. The University of Georgia, by contrast, recommends 500 ppm for iron and sulfur bacteria, because the slime shields them and dissolved iron uses up chlorine⁵. Our take: follow your province or state; where none applies, stay at 200 ppm, which two health and agriculture agencies agree on.
• Volume. Alberta mixes twice the volume of water in the casing, so the chlorine is pushed out into the rock around the well¹.
• Contact time. Alberta leaves it 8 to 48 hours: “The longer the contact time, the better the results”¹. The University of Georgia says at least 24 hours⁵.
• Fresh chlorine. Liquid chlorine loses 20 to 25% of its strength per month in storage¹.
• Clean first if it’s bad. Minnesota says the well should be pumped until clear or physically cleaned before chlorine goes in³. The University of Georgia puts the line at 20%: under that much clogging, a proper shock brings the bacteria back to normal levels; above it, physical cleaning comes first⁵. Acid treatments and scrubbing the casing are jobs for a licensed contractor^2,3.

Our shock chlorination guide has the full procedure. A high-range strip lets you check that the water really reached the dose:

High-range test strips (checks the dose)

Hach Free Chlorine Test Strips, 0–600 mg/L (2890200)

No NSF/ANSI listing found

Range

0–600 mg/L

Colour steps

0, 25, 50, 100, 200, 400, 600

Tests

100

Result

under 1 minute

Strengths

• Reads 200 ppm, which ordinary 0–10 mg/L strips cannot
• No liquid reagents

Drawbacks

• Coarse steps: confirms the range, not an exact number
• Not for checking that the chlorine is gone

Good fit: checking that the recirculating water reached about 200 ppm.
Skip it if: confirming the flush: use a 0–10 mg/L strip.

Expect to repeat it

Shocking “does not completely eliminate iron bacteria from the water system, but will hold it in check,” says Alberta, which repeats it each spring and fall as routine maintenance¹. Saskatchewan also advises shocking wells twice a year⁶. Early on, the University of Georgia finds every six months can be enough⁵. Penn State adds a limit: if you need it more often than about every six months, look at other options, because frequent shocking can damage the water system².

If it keeps coming back: continuous chlorination?

This is where the sources split.

Continuous chlorination for iron bacteria · what each source says

Source	Position
Wisconsin DNR	A pellet chlorinator in the well helps stop bacteria regaining a foothold; it needs state approval first; a carbon filter removes the chlorine after4
Penn State	Down-well pellet droppers, then a whole-house filter for the dead bacteria; a chlorinator in the house does not control bacteria inside the well2
Minnesota	Does not usually recommend continuous injection into the well: it can hide other contamination and cause corrosion3

Our take: this is a decision for your well contractor and local health office, not a product to buy online. Ask whether an in-well chlorinator is allowed where you live.

Prevention

• Only disinfected water should ever go into a well, never lake or pond water³.
• The casing stays capped, watertight and at least 1 ft above ground³.
• Pumps and pipes are kept off the ground during work, and the well is disinfected after any repair^3,4.