Common well water contaminants and solutions

If your well water test just came back with words like arsenic, coliform, manganese, or PFAS, the hard part is figuring out which numbers mean “fix this now” and which ones mostly explain staining, smell, or plumbing damage. Private well owners do not get the automatic treatment and monitoring that city-water customers do. You are the utility.

Most wells do not have one neat problem either. The same report can show iron at 2.4 mg/L, pH at 6.2, and a positive coliform result after a week of hard rain. Treat the wrong problem first and you waste money fast. A softener will not fix tannins. A sediment cartridge will not fix arsenic. Shock chlorination will not fix nitrate.

The short version: what the most common contaminants mean

Use this table the way I do when a lab report lands in my inbox: identify the contaminant, decide whether it is urgent, then pick the first move that matches the chemistry instead of the symptom.

Contaminant	What you usually notice	Number that gets my attention	First move	Deep guide
Coliform / E. coli	Often nothing obvious, sometimes after flooding, heavy rain, or recent well work	Any positive test	Stop guessing, shock chlorinate if appropriate, retest, inspect the wellhead	Coliform bacteria in well water
Nitrate	Usually nothing you can see, smell, or taste	Over 10 mg/L as nitrogen	Use a safe drinking-water source for infants and start source + treatment planning	Nitrates in well water
Arsenic	Nothing you can see, smell, or taste	Over 10 ug/L (10 ppb)	Get speciation if you do not already have it and price point-of-use RO first	Arsenic in well water
PFAS	Nothing you can see, smell, or taste	Any meaningful detection on a PFAS-specific panel	Order a dedicated PFAS test, then compare RO versus certified carbon	Testing well water for PFAS
Iron	Orange staining, rust rings, water that turns orange after sitting	Over 0.3 mg/L	Figure out whether it is clear-water, red-water, or iron bacteria before buying equipment	Best filters for iron bacteria
Manganese	Black staining, slimy black residue, metallic taste	Over 0.05 mg/L	Test alongside iron and pH; oxidation and filtration are usually the conversation	How to remove manganese from your well
Tannins	Tea-brown or yellow water that stays transparent	No health MCL; color above 15 units is widely found objectionable	Do not buy an iron filter blind; confirm tannins and look at tannin-specific treatment	How to treat tannins in well water
Hydrogen sulfide	Rotten egg smell	Any persistent odor	Check whether the smell is in hot water only or both hot and cold	Why your well water smells like rotten eggs
Hardness	Scale, soap scum, dull hair, rough laundry, crust on fixtures	Usually worth treating above 7 gpg	Match the softener size to your actual hardness and iron level	Water softener vs. iron filter
Low pH / corrosive water	Metallic taste, blue-green stains, pinhole leaks, green hair from copper	pH below 6.5	Fix acidity first with a neutralizer before sizing downstream equipment	Why well water turns blonde hair green

The contaminants that are dangerous even when the water looks fine

This is the part homeowners underestimate. The EPA’s private-well guidance says private wells do not get the same treatment and monitoring public systems do, which means a clear glass tells you almost nothing about safety.

Arsenic is the classic example. The EPA’s long-standing arsenic limit is 10 micrograms per liter, and arsenic is odorless and tasteless in water. If your lab result is above that line, I would stop using the water for drinking and cooking until you have a real treatment plan. In most houses that starts with point-of-use reverse osmosis, but arsenic III versus arsenic V matters enough that you do not want a contractor hand-waving past the speciation question.

Nitrate is the one that changes the conversation fastest if you have a baby in the house. The Minnesota Department of Health notes that the EPA drinking-water standard is 10 mg/L as nitrogen, and water above that level can cause methemoglobinemia, the oxygen-starvation problem better known as “blue baby syndrome.” They are also explicit that boiling makes nitrate more concentrated, not less. If nitrate is high, bottled or otherwise safe drinking water comes first, then source investigation and treatment.

PFAS moved from fringe concern to mainstream well-water issue once the EPA finalized the first national PFAS drinking-water rule on April 10, 2024. The agency set enforceable public-water limits of 4 parts per trillion for PFOA and PFOS, and as of May 14, 2025 said it would keep those two rules in place while reconsidering the others. Private wells are still not federally regulated, but those numbers are now the benchmark people use when a PFAS lab result comes back, and a standard county panel usually will not test for them. The full testing breakdown is in this PFAS guide.

Coliform bacteria and E. coli are different from the invisible chemical contaminants above, but they are just as easy to miss if you are judging by appearance. A positive coliform result does not always mean somebody is getting sick today. It does mean you have a contamination pathway that needs attention. Maybe the cap is compromised. Maybe the casing seal is shot. Maybe surface water made its way in after a storm. Either way, a positive bacteria test is never “probably nothing.”

Radionuclides are more regional, but they belong on the shortlist for bedrock wells. The EPA says private-well owners should test for radionuclides every three years. If you are on granite or other bedrock terrain and you have never tested, that gap is worth fixing.

The contaminants that announce themselves

The other bucket is the one homeowners know by sight, smell, or feel. These are not always health emergencies, but they absolutely matter because they stain fixtures, shorten appliance life, ruin laundry, and make people spend money on the wrong treatment.

Iron is the usual first suspect when you see orange rings in the toilet or rusty streaks on sinks and tubs. The EPA secondary standard is 0.3 mg/L. The Minnesota Department of Health breaks iron into three forms that matter in the real world: ferrous iron that runs clear and then turns orange after standing, ferric iron that is already red or yellow at the tap, and organic iron that comes bound up with organics and gets much harder to treat.

Manganese looks like iron’s meaner cousin. The EPA secondary standard is 0.05 mg/L, and the warning signs are black staining, dark slime, bitter metallic taste, and residue that makes fixtures look dirty again five minutes after you cleaned them. If there is also orange or brown goo in the toilet tank, start thinking about iron bacteria or mixed iron/manganese chemistry, not just a generic filter tank.

Tannins are where people get burned by assumptions. The water looks yellow-brown, like weak tea, so they buy an iron filter and nothing changes. The EPA’s secondary standards page says most people find color objectionable above 15 color units, but the bigger practical problem is that tannins often interfere with iron treatment. If the water stays transparent and tea-colored instead of settling out orange particles, tannins belong high on your list.

Hydrogen sulfide is the rotten-egg smell everybody remembers. The fix depends on one simple test: smell the cold water, then the hot. If both smell, the source is likely in the well water itself and you are usually discussing oxidation plus filtration. If only the hot water smells, the water heater anode rod jumps way up the suspect list and the fix can be dramatically cheaper. This sulfur guide walks through that fork in the road.

Hardness is not a contaminant in the same health-risk sense as arsenic or nitrate, but it is still a real problem. Scale on faucets, soap scum on shower glass, scratchy towels, dull hair, and a water heater full of mineral rock all trace back to calcium and magnesium. A softener is often the right answer, but not if iron is also present at levels that will foul the resin. That is how homeowners end up needing an iron filter before the softener.

Low pH belongs in this section because corrosive water behaves like an invisible plumbing thief. The EPA’s secondary standard range for pH is 6.5 to 8.5. Below that, you start seeing metallic taste, blue-green stains, copper pinhole leaks, and sometimes the exact copper issue that turns blonde hair green. If pH is low, the neutralizer usually comes first.

Match the fix to the contaminant, not to the symptom

This is where most four-figure mistakes happen. Homeowners shop by symptom, but treatment works by chemistry.

If the result is bacteria, the first conversation is about shock chlorination, well repair, and possibly UV or continuous disinfection. If the result is arsenic, nitrate, PFAS, or radionuclides, the first serious quote is often point-of-use reverse osmosis at the kitchen sink, because these are drinking-water contaminants more than shower contaminants. If the result is iron, manganese, or hydrogen sulfide, you are usually talking about oxidation plus filtration. If the result is hardness, a softener is often right, but only after you account for iron. If the result is low pH, an acid neutralizer belongs upstream of almost everything else.

The well water filtration guide goes deep on equipment, flow rates, and treatment order. The quick version is this:

1. Health contaminants determine what you should drink now.
2. Corrosion and pH issues often determine what has to be installed first.
3. Iron, manganese, sulfur, and tannins determine the heavy lifting in the middle of the treatment train.
4. Hardness usually gets treated after iron and manganese, not before.

That order is not theory. It is the difference between equipment that lasts 10 years and equipment that clogs, scales, or fails early.

When a lab report shows three problems at once

A common real-world example looks like this: pH 6.1, iron 1.8 mg/L, hardness 15 gpg, and intermittent coliform positives after storms. That is not one filter. That is a wellhead inspection, then usually an acid neutralizer, then iron treatment, then a softener, then possibly UV if the bacteria issue persists after the structural problem is fixed.

Another common example: nitrate at 12 mg/L, everything else mostly fine. That is not a whole-house iron tank. It is usually safe interim drinking water plus under-sink RO while you figure out whether the source is septic, agriculture, runoff, or a compromised shallow well.

This is why I push testing so hard. A $150 to $300 lab panel beats a $2,500 guess every time.

Your next move

Pull out your most recent water test and highlight four things: any positive bacteria result, any nitrate or arsenic number, any PFAS detection, and any pH below 6.5 or iron above 0.3 mg/L. That 60-second sort tells you whether you are dealing with a drinking-water safety issue, a nuisance issue, a plumbing-corrosion issue, or some combination of the three.

If you do not have a certified test from the last year, that is the move this week. Not a filter. Not a sales call. A test. The right treatment only gets obvious once the right numbers are on paper.