Waterborne viruses like norovirus and rotavirus are highly contagious pathogens that cause severe gastroenteritis with vomiting and diarrhea, affecting millions globally and particularly dangerous for young children and elderly individuals. Their extremely small size (typically 20-100 nanometers) allows them to pass through many conventional filters, and they can remain infectious in water for extended periods, requiring advanced treatment methods for effective removal.

Raoultella terrigena is an opportunistic bacteria found in water and soil that can cause respiratory infections, urinary tract infections, and bloodstream infections, primarily in people with weakened immune systems or underlying health conditions. While less common than other waterborne pathogens, it's increasingly recognized as an emerging concern because it can be resistant to multiple antibiotics and persist in water distribution systems.

Presence of E. coli in tap water signals recent fecal contamination and potential presence of dangerous pathogens, with pathogenic strains causing severe disease and death. Zero tolerance standards exist for E. coli in treated water because any detection indicates treatment failure.

A protozoan parasite causing severe gastrointestinal illness with weeks of debilitating diarrhea, Giardia enters tap water from contaminated groundwater and surface water sources near sewage. This resistant pathogen survives municipal chlorination and causes outbreaks in water-stressed regions and during infrastructure emergencies.

Cryptosporidium is a parasite that survives in water despite chlorine treatment, causing severe diarrhea lasting weeks, especially in children, elderly, and immunocompromised people. Its tough outer shell makes it resistant to standard disinfection, allowing it to pass through most water treatment systems and cause outbreaks.

Developed from chemical warfare nerve agents and adapted for agriculture, these pesticides irreversibly block nerve signal transmission causing acute poisoning and chronic neurological disease. Prenatal exposure causes permanent developmental harm including reduced IQ and increased Parkinson's disease risk.

These water-soluble insecticides enter groundwater through agricultural runoff and cause acute neurological effects (tremors, headaches, muscle weakness) plus chronic organ damage at higher exposures. Some compounds are linked to cancer and act as endocrine disruptors affecting hormone systems.

Atrazine is the most common pesticide contaminant in U.S. drinking water (found in 41% of public supply wells), acting as a potent endocrine disruptor affecting reproductive hormones at extremely low doses. Linked to preterm delivery, low birth weight, and genital defects, this herbicide remains widely used in the U.S. despite EU ban since 2004.

These represent the second-largest pesticide category globally and act as endocrine disruptors affecting estrogen, androgen, and thyroid systems while accumulating in cerebrospinal fluid. Multiple triazole compounds (2-7 simultaneously) commonly contaminate water together, creating cumulative hormone disruption risks.

Sulfonylurea and urea-based herbicides used on wheat, corn, soybeans, and rice enter groundwater through agricultural runoff with 83% of Midwestern water samples detecting multiple herbicide residues simultaneously. While individually less toxic than organophosphates, cumulative herbicide burden represents ongoing low-level exposure to plant-growth-disrupting compounds.

These "forever chemicals" with exceptionally strong carbon-fluorine bonds persist for potentially thousands of years in the environment and accumulate in human blood and tissues with half-lives over 8 years. Over 95% of Americans have detectable PFAS in their blood from decades of exposure to non-stick cookware, waterproof clothing, firefighting foam, and food packaging.

The most infamous PFAS, discovered in drinking water supplies serving millions and definitively linked to kidney cancer, testicular cancer, thyroid cancer, and immune suppression. Used for 60+ years in non-stick coatings and industrial processes before its cancer risk became undeniable, this compound continues contaminating groundwater near factories and airports.

Originally used in Scotchgard fabric protection and aqueous film-forming foams at military bases and airports, PFOS was phased out in 2000 but continues contaminating tap water three decades later. Bioaccumulating in tissues with 5+ year half-lives, PFOS causes liver injury, developmental effects, and immune suppression at extremely low doses.

An emerging PFAS increasingly detected in drinking water as manufacturers replace older compounds, this chemical shows persistence and bioaccumulation similar to PFOA and PFOS. The EPA recently designated PFDA as a regulated PFAS, acknowledging health risks from this replacement compound.

This emerging PFAS is increasingly found in drinking water and shows endocrine-disrupting effects and developmental toxicity in research studies. As an alternative to PFOA, PFNA demonstrates how banning one forever chemical simply shifts production to replacement compounds that may be equally persistent.

One of the EPA's newly regulated PFAS compounds, this short-chain alternative was developed to replace longer-chain compounds but shows similar persistence and bioaccumulation. Detection in tap water near manufacturing and airport sites indicates ongoing contamination from industrial use.

This long-chain PFAS accumulates in human serum and shows potential for endocrine disruption, adding to the cumulative burden when multiple PFAS compounds contaminate water simultaneously. Like other replacement PFAS, this compound was introduced precisely because it was less studied, perpetuating a cycle of substituting unknown chemicals for proven toxins.

A sulfonate-based PFAS increasingly used as a replacement for PFOS in industrial applications, PFHxS shows similar persistence and bioaccumulation as its predecessor. This emerging contaminant is now detected in drinking water supplies globally as manufacturing shifts continue.

A short-chain PFAS promoted as a "safer" alternative to longer-chain compounds, PFBS remains persistent in the environment and bioaccumulates in human tissues. Growing detection in tap water reflects the ongoing replacement strategy where one forever chemical substitutes for another inadequately studied compound.

This long-chain PFAS shows extreme persistence and resistance to environmental degradation, accumulating in human serum and organs with potential for long-term toxicity. Detection in tap water indicates industrial contamination from manufacturing facilities using this compound.

A long-chain sulfonate PFAS with similar properties to PFOS, PFDS persists indefinitely in the environment and bioaccumulates progressively in human tissues. This compound demonstrates the futility of "safer" PFAS replacements—the problem remains fundamentally the same regardless of chemical structure.

A mid-chain PFAS with documented endocrine-disrupting potential and bioaccumulation in human serum collected from blood donors. This compound's presence in tap water, while less common than PFOA or PFOS, represents growing contamination from industrial use.

A short-chain sulfonate PFAS increasingly detected in drinking water as manufacturers seek alternatives to regulated longer-chain compounds. Persistence in water and bioaccumulation in tissues make this replacement chemical equally problematic despite lower regulatory attention.

An alternative PFAS structure with different but similarly concerning toxicity profiles including developmental and reproductive effects. The chemical diversification of PFAS compounds creates a moving target for regulation and treatment, with new variants appearing faster than health effects can be studied.

Beyond the major PFAS compounds, your tap water likely contains additional PFAS acids and sulfonates with varying toxicity profiles and persistence. The full extent of health effects from this entire class of 14,000+ compounds remains unknown because many were never studied for long-term human exposure.

A potent neurotoxin with no safe exposure level, lead from aging pipes and solder causes permanent brain damage in children including reduced IQ, learning disabilities, and behavioral problems. Even the EPA's "safe" level (15 ppb) causes measurable cognitive harm, yet infrastructure replacement remains inadequate.

Leaching from pipes in homes with acidic water or new plumbing, copper becomes toxic at excess levels causing gastrointestinal distress and organ damage despite being an essential nutrient at proper levels. First-draw water (sitting overnight in pipes) can contain 10x higher copper than running water, yet most people use this water for morning coffee and infant formula.

While not toxic at normal levels, elevated iron in tap water causes reddish-brown staining on fixtures and laundry, metallic taste, and growth of iron bacteria producing "red slime" biofilm that harbors pathogens. This aesthetic problem signals broader water quality issues suggesting other metals including lead are also leaching.