Clean drinking water is essential, but increasingly scarce. From pesticides in our rivers to toxic chemicals in our groundwater, water pollution affects not just ecosystems but our health, homes, and future. Let’s break down the types, causes, and sources of drinking water contaminants. Plus, discover the best way to filter hundreds of contaminants from your water.

Water contamination refers to the presence of harmful substances—physical, chemical, biological, or radiological—in water. These substances degrade water quality and can pose serious health risks. While some contaminants occur naturally, most are the result of human activity.

To effectively combat water pollution and safeguard our water resources, it’s essential to understand both where the pollution comes from and what type of water body is being impacted, whether it's groundwater, surface water, or ocean water.

Water pollution is generally categorized by its source, which falls into three main types:

• Point Source Pollution: Originates from a single, identifiable source. Examples include wastewater discharged by factories, leaking septic systems, and oil or chemical spills. Even though the pollution comes from a specific point, its impacts can extend far downstream, affecting miles of waterways and ocean ecosystems.

• Nonpoint Source Pollution: Comes from scattered, diffuse sources making it much harder to trace and regulate. This category includes agricultural runoff carrying fertilizers, pesticides, and animal waste. Because there’s no single responsible party, tackling this form of pollution requires widespread policy, infrastructure, and behavioral changes.

• Transboundary: Occurs when contaminated water crosses national or regional boundaries. This can result from sudden disasters like offshore oil spills and the slow drift of industrial, agricultural, or municipal pollutants downstream.

Natural Sources

Not all water pollution comes from human activity—some contaminants are naturally occurring. As groundwater and surface water flow through soil and rock, they can pick up naturally present elements that pose health risks. These include:

• Radioactive chemicals like radon and uranium

• Heavy metals such as arsenic, lead, and mercury

• Other naturally present minerals that, in elevated concentrations, can contaminate drinking water supplies

While these substances occur in nature, their presence in water isn't always safe. Geological formations, climate conditions, or human disturbance (like mining or drilling) can elevate these contaminant levels—making water unsafe without proper treatment.

Agriculture

Agriculture consumes roughly 70% of the world’s surface water—and it’s also a leading cause of water pollution. In the U.S., farm runoff is the top source of pollution in rivers and streams, and a significant contributor to contamination in lakes, wetlands, estuaries, and groundwater. When it rains, fertilizers, pesticides, and animal waste are washed from fields into nearby water bodies, triggering harmful algal blooms and spreading bacteria, viruses, and excessive nutrients like nitrogen and phosphorus.

Each year, U.S. farms apply more than 12 million tons of nitrogen fertilizer and produce over 1.4 billion tons of manure—much of which is spread back onto fields. As a result, farm runoff is often heavily contaminated with nitrogen, phosphorus, and a range of pesticides.

Water Infrastructure And Treatment

Aging water infrastructure—including pipes, storage tanks, and distribution systems—is a growing concern across the United States. As these systems deteriorate, contaminants like lead, copper, and chemicals can leach into drinking water. In the U.S., aging infrastructure poses its own risk:

To make water safe, public utilities treat it to remove contaminants, but some treatments can unintentionally cause problems. Certain chemical treatments may interact with materials in pipes or with the water’s own chemistry, leading to corrosion or the formation of new harmful substances. Regular monitoring and adjustment of treatment processes are essential to keep both water quality and infrastructure stable.

Disinfection is a critical step in preventing waterborne diseases, but it comes with trade-offs. Chemicals like chlorine are commonly used to kill pathogens, yet when they react with organic matter—such as fertilizer runoff or animal waste—they can form toxic disinfection byproducts. Scientists have identified more than 600 of these byproducts, some of which are linked to DNA damage and cancer. Minimizing organic material in source water is key to reducing their formation.

Wastewater And Storm Water Runoff

Wastewater is used water from homes, businesses, farms, and factories. It includes everything from sewage flushed down toilets to chemical-laden discharge from industrial activities. It also encompasses stormwater runoff, which occurs when rain flows over roads, rooftops, and yards, picking up pollutants like road salts, oil, grease, microplastics, and fertilizer residue before entering local waterways—often without any treatment.

Modern wastewater treatment plants are designed to remove harmful substances, including pathogens, nutrients like phosphorus and nitrogen, and heavy metals. In the U.S., these facilities process about 34 billion gallons of wastewater daily. But even advanced systems can’t fully eliminate contaminants such as PFAS, personal care products, and pharmaceutical residues which increasingly show up in treated water.

From industrial runoff and agricultural waste to aging infrastructure and emerging contaminants, our water faces threats from every direction—many of which slip through the cracks of regulation and treatment.

How to Remove Contaminants From Water

At Clearly Filtered, we believe everyone deserves access to clean, safe, and truly filtered water. Our water filtration systems are independently tested to remove up to 99.99% of hundreds of contaminants—including those often missed by traditional systems—like PFAS, lead, pesticides, pharmaceutical residues, and more.  Tap here to see our full list of test results. 

Clean water shouldn’t be a luxury—it should be a guarantee. Shop our full line of advanced filtration systems and make clean water part of your routine.