We all expect the water from our tap to be clean, clear, and safe. But have you ever stopped to think about what might actually be in it?

When most of us hear the word “contaminant,” we picture something obviously gross—like dirt, bugs, or a murky glass of water. But in reality, a contaminant in drinking water can be invisible, odorless, and even legal, yet still harmful over time.

So what exactly counts as a contaminant? How do these unwanted substances end up in the water we drink every day? What is the best way to remove water contaminants?

Let’s take a closer look.

According to the Safe Drinking Water Act (SDWA), a contaminant is any physical, chemical, biological, or radiological substance or matter in water. This includes both naturally occurring elements, such as minerals, and synthetic substances introduced by human activity.

The SDWA was created to make sure that all public drinking water in the U.S. meets certain safety standards. It gives the Environmental Protection Agency (EPA) the authority to set and monitor these national guidelines—and it’s backed by federal law.

What Does the SDWA Do?

• Sets Safety Standards: The SDWA gives the EPA the power to set legal limits on over 90 contaminants in drinking water—things like lead, chlorine byproducts, arsenic, and bacteria.

• Monitors Public Water: It requires public water suppliers to test regularly and fix problems to stay compliant.

• Keeps You Informed: Every water provider must issue an annual water quality report, so you can see what’s in your water.

In short, it was designed to help protect your tap water from harmful contaminants.

Why It Matters

The SDWA was a major milestone in protecting our tap water. It laid the foundation for clean water standards across the U.S., but it doesn’t mean your water is completely free of harmful contaminants.

To help keep drinking water safe, the EPA sets legal limits called Maximum Contaminant Levels (MCLs) for certain substances. These limits guide how water is treated and disinfected across the country.

But here’s the catch:

• MCLs aren’t updated very often.

• Many emerging or less-studied contaminants aren’t regulated at all.

• Some limits are still higher than what many health experts consider safe.

New contaminants like PFAS (also called “forever chemicals”) are becoming more common in water supplies—but many are still being studied or not regulated at all.

Even at “legal” levels, certain contaminants in drinking water have been linked to serious health concerns, including:

• Reproductive and developmental problems

• Neurological damage

• Liver and kidney issues

• Immune system disruption

• Increased cancer risk

According to the EPA, there are four main categories of contaminants in drinking water:

Physical contaminants primarily impact the physical appearance or other physical properties of water. 
These are the things you can actually see or feel in your water—like dirt, sand, or bits of leaves. They usually come from soil erosion and end up in lakes, rivers, and streams. While they’re not always dangerous on their own, they can make sink water look cloudy or dirty.

Chemical contaminants are elements or compounds.
These can be natural or man-made substances, and they cover a pretty wide range. Think of things like bleach, pesticides, nitrates, metals, and even pharmaceuticals. Some come from farming or industrial runoff, while others seep in from older plumbing or water treatment processes.

Biological contaminants are organisms in water.

Also known as microbes, these are tiny living organisms—like bacteria, viruses, parasites, and protozoa—that can sneak into water and potentially make you sick.

Radiological contaminants are chemical elements with an unbalanced number of protons and neutrons resulting in unstable atoms that can emit ionizing radiation. 

These are less common, but still worth mentioning. Radiological contaminants include elements like uranium, cesium, and plutonium. They’re unstable atoms that can release radiation, and they usually come from natural deposits or industrial activity.

If you’ve ever wondered what’s really in your tap water, our free database has the answers. It compiles official test results from public water supplies so you can see exactly what’s coming out of your faucet, how it might affect your health, and how to protect yourself and your family.

At Clearly Filtered, we go beyond the basics. Our filters don’t just reduce chlorine or mask bad smells—they’re built to remove up to 99.99% of 365+ contaminants, including the ones that matter most: lead, PFAS, pesticides, pharmaceuticals, microplastics, and more. Tap here to see our test results and how we filter water contaminants.

All of our systems are powered by our breakthrough Affinity® Filtration Technology so you can trust that your water is clean, safe, and healthy—no matter where it comes from. Shop our full line of advanced filtration systems and make clean water part of your routine.