Nothing will tell you it is there

Every other problem in this cluster announces itself. Iron stains the laundry. Sulfur smells. Hardness leaves scale on the kettle. Acidic water turns the sink blue-green.

Arsenic does none of that. It is colourless, tasteless and odourless at every concentration that matters. There is no glass test, no smell test, no visible symptom. The only way to know is to send a sample to a lab.

That is the whole argument for this page.

How common is it

Minnesota Department of Health: “About 10 percent of Minnesota’s private wells have arsenic levels higher than 10 µg/L.”

One in ten. That is a Minnesota figure and it reflects Minnesota geology — arsenic “occurs naturally in rocks and soil… and can dissolve into groundwater,” so prevalence tracks bedrock rather than state lines and the number does not transfer elsewhere.

What it does establish is that arsenic in private wells is common where the geology favours it, not a rare event.

The limit, and who it applies to

EPA allows a maximum of 10 micrograms per litre in community water systems.

Your well is not a community water system. Nobody tests it against that number, nobody reports on it, and nothing changes if it is exceeded. The standard is the right benchmark for reading your own result — it just does not come with anyone enforcing it.

Why it matters at low levels

Minnesota Health is specific: “Consuming water with even low levels of arsenic over a long time is associated with diabetes and increased risk of cancers of the bladder, lungs, liver, and other organs.”

Also associated: cardiovascular and respiratory disease, reduced intelligence in children, and skin problems.

Note the framing — low levels over a long time. This is a cumulative exposure problem, not an acute one. There is no moment at which the water tastes wrong and you stop drinking it.

Testing

Minnesota Health’s guidance is modest: “Test your well for arsenic at least one time beyond the initial well water test when the well is first constructed.”

Once, deliberately, is most of the value. Arsenic comes from the rock the water moves through, so unlike bacteria it does not spike after heavy rain or vary with a failed well cap. A clean result on a stable aquifer stays informative.

Treatment

Minnesota Health lists seven methods that reduce arsenic:

  • Reverse osmosis
  • Distillation
  • Adsorptive media
  • Anion exchange
  • Ozonation and filtration
  • Oxidation filtration
  • Chlorination and filtration

We are not ranking these by removal efficiency, and you should be careful of anyone who does casually. Arsenic occurs in more than one chemical form, and how well a given technology performs depends on which form is present. A removal percentage quoted without naming the species it applies to is not a usable number.

If a supplier quotes you one, the question to ask is: which form of arsenic, and how do you know which one is in my water?

Where point-of-use treatment sits relative to the rest of the system is worked through in the sizing method. The rest of the cluster starts at well water treatment.