Homeowner collecting a well water sample

Arsenic: Above 10 ppb in Well Water? Match Your Results to a Fix

If your well water tests above the EPA’s benchmark of 10 parts per billion, stop drinking and cooking with it right away. Private wells are not federally regulated, so testing through a certified lab is the only way to know where you stand. Switch to bottled or treated water for drinking and cooking, then arrange a certified total arsenic test and retest in six months if this is a new detection.

TL;DR:

  • Use a state certified laboratory rather than a home strip, because strips may miss contamination near 10 ppb; total arsenic is the standard test.
  • Below 5 ppb, retest periodically; from 5 to 10 ppb, confirm results, and at 250 ppb or higher, prioritize whole house treatment or another source.
  • Reverse osmosis or distillation treats drinking water at one tap, while adsorption media or anion exchange treats the whole house; arsenite often needs oxidation first.
  • Before selecting a system, compare iron, manganese, pH, hardness, and sulfate alongside arsenic, because these water conditions affect treatment choice and media life.
  • Test treated water after installation and annually; systems maintained by homeowners failed more often than those maintained by vendors in a study.
Gridwiseliving
Make Well Water Part of a Resilient Home
Gridwise Living offers solar systems and other practical home solutions for people seeking greater self-reliance, alongside advice from a certified water professional.

Table of Contents

What Arsenic Is and How It Gets Into Your Well

Arsenic has no smell, taste, or color, so you cannot detect it by drinking the water or looking at it. It enters groundwater naturally from certain rock formations and soil, and in some areas from historical pesticide use or mining activity near the well site.

Arsenic shows up in two forms with very different behavior in water:

  • Arsenite, or As(III), is more toxic and harder to remove from water than the other common form.
  • Arsenate, or As(V), binds more easily to treatment media and is generally easier to filter out.
  • Most lab reports show total arsenic rather than breaking out the two forms unless you specifically request speciation testing.

Ingestion through drinking water and cooking is the exposure route that matters most for long-term health risk, while showering, bathing, and laundry carry comparatively low risk at typical household concentrations.

Who Needs to Test and How Often

Every household relying on a private well should test for arsenic at least once, since there is no regulatory body checking the water for you. Levels can vary significantly between two wells on the same street, so a neighbor’s clean results tell you nothing about your own supply.

  • Test your well at least once regardless of how long you have lived on the property.
  • Retest every one to three years once arsenic has been detected, or sooner if you notice a change in taste, color, or sediment.
  • Retest after drilling a new well, adjusting pump depth, or following a nearby earthquake that could shift groundwater flow.
  • Confirm any new positive result with a second test about six months later before committing to a treatment system.

How to Test Your Well Water for Arsenic

A certified laboratory test, not a home dip-strip kit, is what you need for a reliable arsenic reading. Home kits can screen for rough contamination but typically lack the sensitivity to confirm levels near the 10 ppb benchmark, so a state-certified lab is the right starting point.

  1. Contact a state-certified water testing lab and request a total arsenic test; they will mail or provide sample bottles with instructions.
  2. Run the cold tap you use for drinking and cooking for several minutes to flush standing water from the line.
  3. Collect the sample directly into the lab-provided bottle without touching the inside of the cap or bottle.
  4. Label the sample with the date and location, then refrigerate or ship it according to the lab’s turnaround instructions.
  5. Ask about speciation testing only if you suspect industrial contamination or unusual chemistry; it is rarely needed for a standard residential well.

Pro Tip: Keep bottled or filtered water on hand for drinking and cooking while you wait on lab results, especially if a previous test or a neighbor’s well has shown elevated arsenic.

Turnaround is typically a week or two depending on the lab, and a standard total arsenic test is a modest cost compared to the price of a treatment system.

Reading Your Results: What the Numbers Mean

Lab reports list arsenic in parts per billion (ppb) or micrograms per liter (µg/L), which are equivalent units. The figure you’re comparing against is the EPA’s Maximum Contaminant Level of 10 ppb, the health-based benchmark set for public water systems. Private wells aren’t covered by that rule, but it’s the standard homeowners use to judge their own results.

  • Below 5 ppb: low concern, continue periodic retesting on schedule.
  • Between 5 and 10 ppb: worth confirming with a retest and starting to research treatment options.
  • Above 10 ppb: treat the water or switch to an alternative source for drinking and cooking.
  • At 250 ppb or higher: whole-house treatment or a completely different water source becomes the priority.

Ask your lab about speciation if treatment doesn’t bring levels down as expected. As(III) is neutral at typical groundwater pH and resists adsorption, so it often needs an oxidation step before standard media can remove it effectively.

Treatment Options: Matching the System to Your Water

Two broad categories cover most residential arsenic treatment: point-of-use (POU) systems that treat water at a single tap, and point-of-entry (POE) systems that treat everything coming into the house.

  • Reverse osmosis and distillation are effective POU choices for drinking and cooking water, though RO produces a wastewater stream and distillation uses meaningful electricity per gallon.
  • Adsorption media, including granular ferric oxide and iron-impregnated resins, works well as a POE solution when arsenic is the main concern and other chemistry is in range.
  • Anion exchange is another POE option, particularly where sulfate levels are low enough not to compete with arsenic for exchange sites.
  • Pre-oxidation is often necessary for As(III) before adsorption or exchange media can remove it reliably, per EPA technical guidance on treatment technologies.
  • Iron, manganese, and hardness should be addressed with pretreatment, since these compounds foul arsenic media and shorten its working life.

Pro Tip: Bring a full water chemistry panel, not just the arsenic number, when you’re sizing a treatment system; pH, iron, manganese, and sulfate all affect how long your media lasts.

Maintenance matters as much as the initial installation; understanding how to choose a pool sanitation system can provide insights into maintaining water quality and residuals effectively. Media has a finite capacity and needs replacement on a schedule, cartridges in RO systems need periodic swaps, and anion exchange resin requires regeneration or replacement. A CDC-reviewed study of households in Maine and New Jersey found that treatment systems can cut arsenic by up to two orders of magnitude, with many treated samples falling below 1 µg/L, but systems installed and maintained by homeowners failed noticeably more often than vendor-maintained systems. Test your treated water right after installation, then at least annually afterward to confirm the system is still performing.

Choosing and Maintaining the Right System

Before you call a vendor, gather the numbers that actually determine which system fits your well.

  1. Note your untreated arsenic concentration and whether the lab identified competing anions like sulfate or phosphate.
  2. Ask the lab or a knowledgeable vendor what proportion of your arsenic is As(III), since that changes whether pre-oxidation is needed.
  3. Calculate your household’s peak water flow needs to size a POE system correctly.
  4. Confirm the system carries NSF certification specifically for arsenic reduction, not just general filtration.
  5. Ask vendors what treated-water level they’re targeting, typically 5 ppb or lower, plus their maintenance schedule, waste handling process, and warranty terms.

Upfront cost and ongoing maintenance both factor into the decision, and some states or local health departments offer assistance programs for well treatment, so it’s worth asking before you commit to a system. Once installed, set testing points for both the raw well water and the treated output, and watch for signs like reduced flow, unusual taste, or a visible return of staining, any of which can signal the media needs attention sooner than scheduled.

Mapping Your Lab Report to the Right Fix

A lab report full of numbers doesn’t do much good if you can’t translate it into a decision. Here’s a rough guide: results under 10 ppb generally call for verification and, if you want extra peace of mind for drinking water, an under-sink reverse osmosis unit. Results between 10 and 250 ppb usually point toward adsorption media or anion exchange, chosen based on your iron, manganese, and sulfate levels. Results at or above 250 ppb usually justify whole-house treatment or seriously considering an alternative water source.

  • Bring these numbers when shopping for a system: total arsenic, iron, manganese, pH, hardness, and sulfate.
  • Test treated water right after installation, then annually going forward.
  • Retest your untreated source every one to three years to catch changes in groundwater chemistry.

Our guidance on matching filtration to lab results walks through this mapping in more detail, and our sampling checklist covers the collection steps if you want a visual reference before your first test.

Arsenic in Garden Produce Grown With Well Water

Water with elevated arsenic doesn’t just raise a concern at the kitchen tap. Irrigating vegetable beds or greenhouse crops with contaminated well water lets plants take up arsenic through their roots, and some crops concentrate it more than others. Rice and leafy greens are commonly flagged as higher uptake crops, while fruiting vegetables like tomatoes and peppers tend to accumulate less in the edible portion.

Comparison of arsenic uptake across garden crops

If your well tested above the 10 ppb benchmark, the safest move is treating the water you use for irrigation the same way you’d treat your drinking water, rather than assuming garden use is low risk. Raised garden beds filled with tested, clean soil and irrigated with filtered or municipal water sidestep the issue entirely for anyone growing food at home. For container gardening or a greenhouse setup, routing treated water specifically to planting beds, separate from untreated hose bibs, keeps contaminated water out of your food chain without requiring a full-property system upgrade.

Soil testing alongside water testing gives a fuller picture, since some arsenic in garden soil predates well contamination and comes from historical pesticide use. Rotating crops, choosing raised beds with fresh soil, and prioritizing lower-uptake vegetables in any bed irrigated with untreated well water are practical steps while you sort out a permanent water treatment plan.

Filtration for Off-Grid and Solar-Powered Homes

Running arsenic treatment on an off-grid or solar-powered property adds a layer of planning most homeowners on municipal power never think about. Reverse osmosis systems and distillation units draw continuous electricity, which can strain a modest solar setup, especially during low-sun stretches when battery reserves are already tight.

Adsorption media and anion exchange systems are generally better suited to off-grid homes because they rely on water pressure rather than constant electrical draw, aside from an occasional pump cycle. If your property runs on a solar generator or battery bank, sizing that system to handle periodic treatment demands, not just lighting and appliances, avoids surprises when the filtration system needs to run.

Pairing a point-of-entry arsenic system with a solar energy setup means checking the system’s power draw against your panel and battery capacity before installation, not after. For homes using rainwater as a backup or supplemental source, our guide to making rainwater drinkable covers first-flush diverters and UV treatment, which pair well with an off-grid lifestyle when well water alone can’t be fully trusted or is still awaiting treatment.

Filtration for Off-Grid and Solar-Powered Homes — overview diagram

A Practical Note on Priorities

Test first. Protect your drinking and cooking water immediately if results come back elevated. Then choose a system matched to your actual water chemistry, not a generic recommendation, and verify it’s working with regular retesting rather than assuming it will perform forever.

— Gridwise

This article is general information, not a substitute for advice from a qualified doctor. Consult a qualified healthcare professional about your own circumstances before acting on anything here.

FAQ

What are the different forms of arsenic?

Arsenic occurs mainly as arsenite, or As(III), and arsenate, or As(V), in groundwater. As(III) is more toxic and harder to remove because it stays neutral at typical groundwater pH, while As(V) binds more readily to treatment media.

How do I test for arsenic in well water?

Order a total arsenic test from a state-certified laboratory, which will provide sample bottles and collection instructions. Flush your cold tap for a few minutes, collect the sample from the tap you use for drinking, and ship or deliver it to the lab as directed.

What is inorganic arsenic?

Inorganic arsenic refers to arsenic compounds bound to elements like oxygen or chlorine rather than carbon, and it’s the form most commonly found in groundwater and well water. It’s also the form most lab reports measure when they report total arsenic.

How do I remove arsenic from drinking water?

Reverse osmosis and distillation are effective point-of-use options for treating drinking and cooking water specifically. For whole-house treatment, adsorption media or anion exchange systems work well, though pre-oxidation is often needed for As(III) before these methods remove it reliably.

How often should I retest my well for arsenic?

Retest every one to three years once arsenic has been detected, and confirm any new positive result again after about six months. Retest sooner after drilling a new well, changing pump depth, or any event that could shift groundwater flow.

Sources

Back to blog