Well Water: What You’re Now Responsible For

First, what kind of well do you have?

It sounds basic, but the type of well you own tells you most of what you need to know about its risks — and almost nobody who inherited a well knows which kind it is. There are three, and they’re genuinely different in how well they keep contamination out.

• Dug wells — wide, shallow, often old, sometimes lined with stone or brick. They pull from close to the surface, which makes them the most exposed to whatever’s soaking down from the yard above: bacteria, runoff, whatever’s nearby. If you have an old wide well with a concrete lid, this is probably it, and it deserves the most caution.
• Driven wells — a pipe driven into shallow groundwater. Also relatively shallow, also more exposed than a deep well, though better sealed than a dug one.
• Drilled wells — a narrow bore drilled deep, cased in steel or plastic, sealed at the top with a cap. A deep, properly sealed drilled well is usually the safest source on this page against bacteria, because depth and casing put distance between your water and the surface. Most modern wells are this kind. The tradeoff to know: the same depth that protects against surface bacteria can mean higher exposure to naturally-occurring bedrock chemicals like arsenic and uranium, which is exactly why a one-time baseline metals test matters even on a good deep well.

Two parts matter no matter the type: the casing (the pipe lining that keeps surface water from running straight down the sides) and the cap (the sealed lid on top). When a well goes bad suddenly, a cracked casing or a bad cap is very often why — a point we come back to below, because it changes what you should do about it.

What’s actually in well water

The useful way to think about well contaminants isn’t a long alphabetical list — it’s where each one came from, because that’s how you actually reason about your own well. Geology is fate. Surface intrusion is usually a neighbor or a weather problem. Your plumbing is your problem. And a few modern ones are nobody’s fault and give you no warning at all.

The testing rhythm every well owner needs

This is the part that replaces the water department, and it’s cheaper and simpler than people expect. There’s a baseline cadence recommended by the CDC and EPA, and then there are triggers that mean “test now, don’t wait.”

• Every year: total coliform bacteria and nitrate. This is the floor — the bare minimum for any well, and it’s inexpensive. Many labs report E. coli alongside coliform automatically.
• Once, as a baseline (and again if conditions change): arsenic, lead, and other heavy metals. Arsenic is geologic — it comes from the rock your water moves through — so your neighbor’s clean result does not clear your well. New owners should run a full baseline panel on moving in.
• Every few years: the slow-moving nuisance set — hardness, iron, manganese, sulfate — since these change gradually and don’t need annual checks.
• Test now, regardless of schedule: after flooding or a submerged wellhead; after any well work (pump, casing, opening the system); when taste, smell, color, or staining changes; if a household member is pregnant or there’s an infant in the home; or if a neighbor reports contamination or there’s a local advisory.

Once the results come back

A lab report is a wall of numbers, acronyms, and limits, and it’s easy to either panic at a number that’s fine or shrug off one that isn’t. The thing to understand is the difference between a legal limit (a hard health ceiling) and a secondary or advisory level (a “this affects taste or staining” threshold) — a distinction that decides whether a result is a health issue or a nuisance one.

Fixing what you found

Here’s the rule that saves the most money: match the treatment to the specific problem, not to a general fear. A filter that’s perfect for one contaminant does nothing for another. Carbon does nothing for nitrate. A softener does nothing for arsenic. A sediment filter does nothing for bacteria. Buying the wrong tool is the single most common well-water mistake.

Because mechanism — not price or marketing — decides what a method actually removes, the honest way to choose is to start from your test result and work toward the method that addresses it:

The configurator takes your situation and hands back what to treat and where; the spectrum lays every contaminant against the technology that removes it. Neither is a shopping list — both start from what you actually have.

What’s different about treating well water

The method pages are written source-neutral — they explain how each technology works for anyone. A few realities are specific to wells, and they’re the ones that trip people up:

• Order matters. Treatment stages have to run in the right sequence — sediment before everything, iron removal before a softener (raw iron fouls the resin), disinfection like UV last. A train built in the wrong order fails quietly. Iron removal, softening, and sediment each have a place in line.
• You have no upstream chlorine. City water arrives already disinfected; yours doesn’t. Every microbial barrier is one you install yourself — which is why UV disinfection comes up so often on wells and almost never on city water.
• UV needs clear water to work. Turbidity shadows organisms from the light, so UV goes at the end of the train, after sediment is removed. For water you know is unsafe, the bar is NSF/ANSI 55 Class A (40 mJ/cm²) — not Class B.
• Nothing is certified for “well water.” Certification is always per-contaminant, never per-source. A filter sold “for well water” is a marketing phrase, not a spec — the honest question is always which contaminant, at what certification. How that plays out with arsenic →

Keeping the well itself healthy

Everything above is about the water. This is about the well — the physical thing in your yard — because a well is a piece of equipment that can fail, and some failures show up in your water first.

Shock chlorination — flooding the well with a strong chlorine dose to kill bacteria — is the standard response to a coliform-positive result, and it’s a job many well owners can do themselves. But two things make it a link-out rather than a step-by-step here: the correct bleach dose depends on your specific well’s water volume (get it wrong low and it fails; wrong high and you can corrode plumbing and overload a septic system), and if a well tests positive again after shocking, that’s the signal it’s a mechanical breach needing a professional, not a re-dose. So the right procedure is your state or county health department’s well-disinfection guidance, which gives dosing tied to well volume and the safety steps for handling concentrated chlorine.

• Check the cap and casing periodically — a cracked cap or casing is the most common entry point for contamination.
• Keep the wellhead clear and above grade so surface water and runoff drain away from it, not toward it.
• After any flooding where water reached the wellhead, assume the well may be contaminated and test before drinking.

When it’s a bigger job than one filter

Some well problems justify whole-house treatment — a microbial issue on the whole supply, iron staining every fixture, hardness scaling every appliance. Others are best handled at a single tap. The honest default: treat the kitchen tap to drinking standard, and treat the rest of the house only for the nuisances that genuinely bother you. Whole-house treatment earns its keep for genuine whole-house problems, not as a reflex.