Arsenic in New Mexico Well Water
New Mexico has among the highest naturally occurring arsenic in drinking water anywhere in the United States. This is the complete guide for private well owners.
Arsenic is invisible. It is tasteless, odorless, and colorless in water. You cannot see it, smell it, or taste it at any concentration. The only way to know if your well has arsenic is to test.
The Scale of the Problem
In 2001, the EPA lowered the arsenic maximum contaminant level (MCL) from 50 ppb to 10 ppb. That single regulatory change put many New Mexico water systems out of compliance overnight — not because the water got worse, but because we finally acknowledged how dangerous these levels are.
The National Research Council estimated that even at 10 ppb — the current legal limit — the lifetime cancer risk is approximately 1 in 300. That's far above the 1-in-10,000 risk level the EPA typically targets for drinking water contaminants.
Bernalillo County Data
The most comprehensive private well testing data we have for the Albuquerque metro area comes from Bernalillo County:
| Metric | Value |
|---|---|
| Wells tested | 425 |
| Percentage above 10 ppb MCL | 10.4% |
| Mean arsenic concentration | 5.2 mcg/L |
| Maximum detected | 100 mcg/L (10x the MCL) |
One in ten wells tested above the federal limit. And those are the wells that were tested — many private wells in the county have never been tested for arsenic at all.
Where Does It Come From?
New Mexico's arsenic has two primary geological sources:
1. Jemez Mountains Volcanism
The Jemez Mountains volcanic complex northwest of Albuquerque is a massive source of arsenic. The silicic volcanic rocks in this system can contain several hundred parts per million of arsenic. As groundwater flows through and around these formations over centuries, it dissolves arsenic from the rock.
This is why communities on the north and west sides of the Albuquerque Basin — Placitas, Rio Rancho, Corrales — tend to have higher arsenic risks. The water has had more contact with volcanic material.
2. Deep Rift-Zone Water
The Rio Grande Rift — the geological feature that created the valley Albuquerque sits in — provides pathways for deep, ancient, highly mineralized water to rise toward the surface. This water has been in contact with rocks for thousands of years and carries dissolved arsenic, among other minerals.
Where faults in the rift zone allow this deep water to mix with shallower aquifers, arsenic concentrations spike. This is a particularly important mechanism in the central and southern parts of the basin.
Health Effects by Concentration
The International Agency for Research on Cancer (IARC) classifies arsenic as a Class I human carcinogen — the highest classification, meaning there is sufficient evidence that it causes cancer in humans.
10-50 ppb (above the MCL but below the old standard)
- Increased risk of high blood pressure
- Increased risk of heart disease
- Skin lesions — thickening, discoloration
- Effects may take years to decades to manifest
Above 50 ppb
- Cancer risk rises to 13 per 1,000 people exposed over a lifetime
- Chronic arsenic poisoning symptoms: fatigue, numbness in hands and feet, skin changes
- Increased risk of bladder, lung, skin, kidney, and liver cancers
The Latency Problem
Perhaps the most insidious aspect of arsenic: cancer can appear up to 40 years after exposure. Someone drinking arsenic-contaminated water today may not develop cancer until decades later — long after the connection between cause and effect has been obscured.
This is why prevention matters. You cannot wait for symptoms.
The Seasonal Arsenic Cycle
A USGS finding that every NM well owner should know about: arsenic concentrations in wells vary by season.
Summer: Heavy pumping draws shallow, lower-arsenic water into the well. Arsenic concentrations tend to be lower.
Winter: Pumps sit idle. Deep, high-arsenic water rises through the wellbore. When you turn the tap on after a period of low use, the water that comes out first may have significantly higher arsenic.
Winter concentrations commonly exceed 12 mcg/L — above the EPA limit — even in wells that test below the limit in summer.
The practical implication: if you test your well in August and get 8 ppb, your winter water may be above 10 ppb. Consider testing in both seasons, or test in winter for a worst-case reading.
Testing for Arsenic
Every private well in central New Mexico should be tested for arsenic at least once. Period. It costs $40-$100 at most labs, and it could save your life.
See our complete testing guide for labs, costs, and free testing opportunities.
Treatment Options
| Treatment | Typical Cost | Notes |
|---|---|---|
| Point-of-use reverse osmosis | $239-$600 system + $150-$700 install | Treats one tap (kitchen sink). Effective for arsenic, uranium, and most contaminants. Most cost-effective first step. |
| Whole-house reverse osmosis | $4,500-$20,000+ | Treats all water entering the home. High upfront cost and significant maintenance. |
| Adsorptive media (iron-based) | Varies; media replacement every 1-3 years | Whole-house arsenic-specific treatment. Works best at pH below 7.0. Popular choice for NM wells. |
For local treatment companies experienced with NM arsenic issues, see our resources page.
Standard carbon filters and water softeners do NOT remove arsenic. A Brita pitcher, a fridge filter, or a basic whole-house carbon filter will not protect you. You need reverse osmosis or arsenic-specific adsorptive media.
Sources
- USGS — Arsenic in Ground Water of the United States
- EPA — Arsenic Rule (66 FR 6976, January 22, 2001)
- National Research Council — Arsenic in Drinking Water (2001 Update)
- IARC — Monographs on the Evaluation of Carcinogenic Risks: Arsenic and Arsenic Compounds
- NMED Drinking Water Bureau — Arsenic Compliance Data for New Mexico
- USGS — Seasonal Variation of Arsenic in Albuquerque Basin Wells
- NM Bureau of Geology — Jemez Mountains Volcanic Arsenic Source Characterization
- Bernalillo County Environmental Health — Private Well Testing Program Data