Nobody is testing your well
EPA’s Maximum Contaminant Levels — 10 mg/L for nitrate, 0.010 mg/L for arsenic — are legally enforceable standards for public water systems. They do not apply to private wells.
That is the single most consequential fact about owning one. The numbers are still the right reference points. There is simply no utility running the tests, no annual report arriving, and no one obliged to tell you if something changed.
Start with a test
Six parameters answer every question the treatment sequence asks: total coliform, nitrate, pH, hardness, iron and manganese — plus arsenic once, because it gives no warning at all. And check the units before the numbers: nitrate is reported as either 10 mg/L nitrate-N or 45 mg/L nitrate, and the same water reads safe or unsafe depending only on which convention the lab used. → What to test for and how to read the report
Two tests that cost nothing
Before any purchase, two diagnostics narrow the problem for free.
The glass test, for iron. Draw a glass and let it stand an hour. Clear at first, then orange-brown particles, means the iron is dissolved and a softener can handle it below 5 mg/L. Particles visible immediately means it is already oxidised — and “oxidized forms of iron and manganese will foul the softener resin.” Different form, different equipment. → Iron in well water
The hot-versus-cold test, for sulfur. If only the hot tap smells of rotten eggs, the cause is the water heater’s anode rod, not the well. That is a part, not a treatment system. → Rotten egg smell
The treatment sequence
Order matters more than brand. Each stage assumes the previous one did its job.
- Neutraliser — if pH is below EPA’s secondary range of 6.5 to 8.5, where EPA lists corrosion as a noticeable effect. Acidic water attacks plumbing and degrades everything installed downstream, and a neutralising filter raises hardness, which changes the softener you size later. → Acidic water and neutralisers
- Iron and sulfur removal — oxidation and filtration, ahead of the softener. → Manganese and black staining
- Softener — above 7 grains per gallon, per Minnesota Department of Health. → Hardness and sizing
- UV disinfection — needs clear water, so it follows particulate removal. → Coliform bacteria and UV
- Point-of-use RO — for nitrate, arsenic or high TDS. Drinking water only; not economic whole-house. → Arsenic · Nitrate
The sizing method works through the arithmetic for each stage.
The one with no warning signs
Iron stains, sulfur smells, hardness scales, acidic water turns sinks blue-green. Arsenic does none of that — it is colourless, tasteless and odourless, and about 10 percent of Minnesota’s private wells exceed the 10 micrograms per litre limit EPA sets for community systems. It is the one that has to be tested for deliberately. → Arsenic in well water
What the numbers mean
Worth keeping two categories apart, because filtration is routinely sold by blurring them.
Aesthetic guidelines. Iron at 0.3 mg/L, manganese at 0.05 mg/L. EPA does not enforce these — exceeding one means staining and taste, not a health risk. Hydrogen sulfide has no standard at all, because it makes water “aesthetically undrinkable long before it reaches harmful concentrations.”
Health limits. Nitrate at 10 mg/L, arsenic at 0.010 mg/L. Enforceable standards set on health grounds for public systems, and the right benchmark for judging your own result.
A stain is a nuisance. Nitrate above 10 mg/L is not. Any page that treats those with equal urgency is selling on fear.