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 diagnostics that cost nothing

Before any purchase, two tests narrow the problem for free. Both are run at your own tap, in under an hour, and each one rules equipment out as well as in.

The glass test, for iron form

Iron form decides the equipment, and a drinking glass identifies it. Draw one and let it stand an hour. Clear at first, then orange-brown particles, means the iron arrived dissolved — and Penn State Extension recommends a softener for iron removal only where dissolved iron is below 5 mg/L.

Particles visible the moment you draw it mean the iron is already oxidised, and “oxidized forms of iron and manganese will foul the softener resin.” Same metal, same number on the lab report, different equipment entirely. It costs nothing, and it is the test that most often prevents a wasted purchase.

→ Iron in well water

The hot-versus-cold test, for sulfur

Which tap smells tells you whether you have a water problem or a water heater problem. Run the cold tap and smell it, then the hot.

If only the hot tap smells of rotten eggs, Penn State Extension attributes that to the heater’s magnesium anode rod, which can chemically reduce sulfates to form hydrogen sulfide, and says replacing it with an aluminium rod should eliminate the odour while maintaining corrosion protection for the heater. That is a part, not a treatment system.

If both taps smell, the hydrogen sulfide is in the groundwater and the method is sized by concentration.

→ Rotten egg smell

The treatment sequence

Order matters more than brand. Each stage assumes the previous one did its job.

  1. 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
  2. Iron and sulfur removal — oxidation and filtration, ahead of the softener. → Manganese and black staining
  3. Softener — above 7 grains per gallon, per Minnesota Department of Health. → Hardness and sizing
  4. UV disinfection — needs clear water, so it follows particulate removal. → Coliform bacteria and UV
  5. 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, which is why Minnesota Department of Health advises testing for it at least once beyond the test performed when the well was constructed — and why about 10 percent of Minnesota’s private wells turn out to exceed 10 micrograms per litre.

Nor can you borrow a neighbour’s result. MDH states arsenic levels “can vary between wells, even within a small area.” Where a test does find arsenic above 10 µg/L and repeat sampling confirms it, MDH recommends an alternate source of drinking water or a treatment system that reduces arsenic.

→ Arsenic in well water

Choose where to start if

  • You have not tested. Start there. Every page in this cluster begins from a number you do not have yet.
  • Laundry stains orange or black. Start with iron and manganese.
  • The cold tap smells of rotten eggs. Start with sulfur.
  • Sinks are turning blue-green. Start with pH, because it changes every stage after it.
  • Nothing is visibly wrong. Start with nitrate and arsenic. Neither announces itself.

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.

→ What to test for, and how to read the lab report → The sizing arithmetic for each stage → City water treatment, if you are on a public system → Public ground water systems, which are regulated where wells are not