Half of the city’s wells contain dangerous levels of arsenic and fluoride—yet most residents remain unaware of the risks
San Miguel de Allende has earned its reputation as one of Mexico’s most beautiful colonial cities. Its cobblestone streets, vibrant art scene, and UNESCO World Heritage status draw thousands of tourists and expats every year. But beneath the surface of this cultural gem lies a crisis that most residents don’t see—and many don’t know about. San Miguel de Allende’s water quality has become a serious health concern that can no longer be ignored.
The water coming from your tap may be making you sick.
Understanding San Miguel de Allende’s Water Quality Issues
According to recent investigations, approximately 50% of the wells supplying water to San Miguel de Allende contain toxic levels of arsenic and fluoride. In some areas, contamination levels are staggering—arsenic at nearly five times the legal limit, and fluoride at more than four times the recommended maximum.
The nonprofit organization Caminos de Agua has been monitoring water quality throughout the region since 2012, and their findings paint a troubling picture. In neighborhoods like Santa Cecilia, Insurgentes, Mexiquito, San Rafael, and Centro, the water contains dangerously high levels of these contaminants.
But here’s what makes this crisis particularly insidious: you can’t see, taste, or smell arsenic or fluoride in your water. The contamination is completely invisible.
Why Is This Happening?
San Miguel de Allende sits above the Upper RÃo Laja aquifer, which serves as the primary water source for more than 680,000 people across northern Guanajuato. This shared resource has been severely overexploited—primarily by large-scale agricultural operations, which consume up to 85% of the region’s total water supply.
As demand has increased and rainfall patterns have become more erratic, the water table has been dropping at an alarming rate of 2-3 meters (approximately 7-10 feet) per year. This is among the most rapidly depleted groundwater sources on the planet.
As wells are drilled deeper to reach the receding water table, they tap into geological layers where arsenic and fluoride occur naturally at higher concentrations. What was once relatively clean water is now increasingly contaminated—not from industrial pollution, but from the very minerals in the earth.
The Health Risks
The dangers of long-term exposure to arsenic and fluoride are well-documented and severe. These aren’t minor inconveniences—they’re serious health threats, particularly for children.
Fluoride contamination leads to dental fluorosis (irreversible brown staining and pitting of teeth) and, in extreme cases, crippling skeletal fluorosis, which causes permanent bone deformities. High fluoride exposure has also been linked to cognitive impairments in children and kidney disease.
Arsenic exposure carries even graver risks. There is no safe level of arsenic consumption. Even small amounts accumulate in the body over time, leading to skin lesions, cardiovascular disease, diabetes, and multiple forms of cancer. Children are especially vulnerable, as their bodies absorb contaminants more quickly.
Dylan Terrell, Executive Director of Caminos de Agua, emphasized the scope of the problem: “This isn’t just about water. It’s about systemic health deterioration—kidney failure, dental and crippling skeletal fluorosis, cognitive issues in children. And it’s all invisible until it’s too late.”
Guanajuato ranks fifth highest in Mexico for kidney disease—a statistic that researchers believe is directly connected to fluoride contamination in drinking water.
It’s Safe for Some Uses, Dangerous for Others
Here’s an important distinction: arsenic and fluoride are only dangerous when consumed—meaning drinking or cooking. The health risks associated with bathing, showering, washing dishes, or doing laundry with contaminated water are extremely low.
However, boiling water does not remove these contaminants. In fact, it concentrates them. As water evaporates during cooking, the minerals and metals remain behind, making the problem worse.
Water Quality Varies by Neighborhood
San Miguel de Allende’s water quality is not uniform across the city. Contamination levels depend on which wells serve your neighborhood, and can change rapidly—sometimes within a matter of days—as the municipal water authority (SAPASMA) mixes water from different wells to meet demand.
According to Caminos de Agua’s monitoring map, the most contaminated neighborhoods include:
- Santa Cecilia
- Insurgentes
- Mexiquito
- San Rafael
- Linda Vista
- Centro
- Las Brisas
- Santa Julia
- Olimpo
Neighborhoods with relatively cleaner water include Independencia, Azteca, Guadiana, Valle del MaÃz, Allende, and Los Frailes—though “cleaner” is relative, and contamination levels can shift.
The reality is this: SAPASMA adds chlorine to city water before it reaches your home, but does not treat for arsenic or fluoride. The infrastructure is old—in many areas, clay water pipes installed centuries ago run in the same trenches as sewer lines. Both systems are in poor repair. At night, when the city turns off water pumps to save power, pressure differences can cause cross-contamination between water and sewage lines.
What Doesn’t Work
Many residents believe they’re protected because they’ve installed water filtration systems. Unfortunately, most commercially available filters cannot remove arsenic or fluoride.
Systems that don’t work include:
- Carbon filters
- UV filters
- “Whole-house” water treatment systems (typically UV + sediment + carbon)
- Ceramic filters (effective for bacteria, but not heavy metals)
- Boiling water
- Adding chlorine
- Nikken filters
These systems are designed to remove biological contaminants and improve taste—not to address dissolved chemical elements like arsenic and fluoride.
Solutions That Actually Work
So what can you do to address San Miguel de Allende’s water quality concerns? Several options exist, though not all are created equal:
Reverse Osmosis (RO) Reverse osmosis systems can remove arsenic and fluoride, but they come with a significant drawback: they waste 50-70% of the water they process. In a region facing severe water scarcity, this is problematic. RO systems also strip out beneficial minerals, leaving you with essentially distilled water.
Electrolysis Filtration A newer technology that removes arsenic, fluoride, heavy metals, and bacteria while preserving beneficial minerals. Unlike reverse osmosis, electrolysis systems waste zero water and maintain full water pressure throughout your home.
Rainwater Harvesting Rainwater is the cleanest, easiest water source to treat for consumption in this region. Despite being in a semi-arid environment, there is sufficient rainfall to meet household needs if properly collected and stored. Organizations like Caminos de Agua have installed over 490 rainwater harvesting systems in surrounding rural communities since 2021.
Bottled Water While not a sustainable long-term solution, bottled water remains the most accessible option for drinking and cooking. However, ensure you’re purchasing from reputable sources, as quality varies.
The Bigger Picture
San Miguel de Allende’s water quality crisis is part of a larger regional emergency. In 2013, the Permanent Peoples’ Tribunal, an international human rights body, recommended that the Mexican government declare the entire Upper RÃo Laja Watershed region an emergency zone due to environmental and health risks.
That declaration never came.
Meanwhile, the crisis worsens. Rural communities surrounding San Miguel have already lost access to water as wells run dry. Three communities that Caminos de Agua works with lost their water supply entirely in recent years. In San Diego de la Unión, just north of San Miguel de Allende, 59 out of 71 communities now have unsafe water.
Mayor Juan Carlos Castillo Cantero of San Diego de la Unión recently made a stark declaration at a press conference: “When we open the tap, we are poisoning ourselves.”
The same is true for many residents of San Miguel de Allende—they just don’t know it yet.
What You Should Do
If you live in or are visiting San Miguel de Allende:
- Do not drink tap water or use it for cooking without proper filtration
- Test your water
- Check your neighborhood on Caminos de Agua’s water quality monitoring map at caminosdeagua.org/water-quality-monitoring
- Invest in proper filtration that specifically removes arsenic and fluoride
- Don’t assume you’re safe because you have a water filter—most don’t remove these contaminants
- Spread awareness—many residents, particularly recent arrivals, have no idea this problem exists
Looking Forward
San Miguel de Allende’s charm and beauty are undeniable. But without sustainable water management, transparent communication about San Miguel de Allende’s water quality, and significant investment in infrastructure and treatment facilities, the city faces an uncertain future.
Local officials, including Mayor Mauricio Trejo, have called on the federal government to intervene, citing the municipality’s lack of resources to build treatment plants and overhaul aging infrastructure. Environmental groups and public health advocates are urging immediate action.
The question is no longer whether San Miguel de Allende has a water problem. The question is: when will San Miguel de Allende’s water quality crisis be treated like the public health emergency it already is?