It’s an innocent mistake, assuming filtered water is clean water…  

But here’s the unfortunate truth: most mainstream water filters—the kind you’d pick up at a grocery store or big-box retailer—rely on activated carbon to clean your water. Carbon reduces chlorine, some sediment, and a handful of common impurities. That’s about it.

Meanwhile, more than 324 contaminants have been detected in U.S. tap water. And many of the dangers making headlines today, the ones linked to things like cancer, cognitive decline, hormonal disruption, and developmental harm in children, can pass right through ordinary carbon filters.

Key Takeaways

• Most mainstream water filters use basic carbon filtration—designed to improve taste, not remove today’s most dangerous contaminants.

• Fluoride, PFAS, lithium, hexavalent chromium, manganese, lead, nitrates, and microplastics are among the threats that could be slipping through.

• Many of these contaminants have no federal drinking water limit—meaning your water utility isn’t required to remove them either.

• Clearly Filtered’s Filtered Water Pitcher targets up to 365+ contaminants—including all eight on this list.

Could the electric vehicles that are supposed to save the planet also be poisoning our drinking water?

The batteries powering EVs require massive amounts of lithium. As mining operations ramp up globally to meet skyrocketing demand, that same lithium is leaching into groundwater and waterways—some of which feed into tap water supplies—at increasing rates.

A USGS-led study found lithium in groundwater exceeding the USGS and EPA’s health-based screening level—the threshold above which health effects become a concern—in 45% of public well samples tested across the U.S. 

The EPA links lithium to kidney damage, thyroid dysfunction, tremors, and cognitive impairment. A UCLA study went further, finding that higher lithium levels in drinking water may raise the risk of autism in children. 

Since conventional water treatment plants aren’t designed to remove it and the majority of carbon filters don’t target it, for most Americans, there’s nothing standing between the lithium in their water and the glass in their hand.

Researchers at the University of New Mexico analyzed brain tissue from people who had died in 2016 and 2024 and found that the amount of plastic in human brains had increased by 50% in just eight years. Brain tissue contained higher concentrations of plastic than the liver or kidneys—and the brain appeared to be the worst at clearing it out.

Even more disturbing: people diagnosed with dementia had up to 10 times more plastic in their brains than those without it.

Meanwhile, a global study found that 83% of tap water samples worldwide contained microplastic fibers.

Once ingested, these tiny shreds of plastic are small enough to cross the blood-brain barrier—a filter that’s supposed to keep harmful substances out of your brain. That means they can carry hormone-disrupting chemicals like PFAS, bisphenols, and phthalates deep into your body’s most protected organ.

Early research links microplastic accumulation to inflammation, oxidative stress, hormone disruption, and perhaps even Alzheimer’s and other forms of dementia.

Carbon filters can catch some larger particles. But the smallest, most dangerous fragments—the ones crossing into your bloodstream and brain—require advanced filtration that goes far beyond what carbon alone can do.

If you’ve ever noticed black stains in your bathtub or a metallic taste in your water, you’ve probably been told it’s just manganese. In other words, it’s an aesthetic issue. Ugly, but harmless, right?

Wrong.

A landmark study in Environmental Health Perspectives found that children exposed to higher levels of manganese in drinking water scored significantly lower on IQ tests. Like lead, manganese is a neurotoxin that developing brains are especially vulnerable to.

Manganese occurs naturally in groundwater across large portions of the U.S., and can legally be in our tap water, as the EPA does not have an enforceable limit. Of course, like the other dangers on this list, mainstream carbon filters were never designed with manganese in mind.

In September 2024, U.S. District Judge Edward Chen ruled that fluoride in drinking water at 0.7 mg/L—the level considered “optimal” in the United States—could pose an “unreasonable risk” to children’s developing brains.

Then, in January 2025, a meta-analysis of 74 studies published in JAMA Pediatrics found a statistically significant link between higher fluoride exposure and lower IQ in children. For every 1 mg/L increase in urinary fluoride, children’s IQ decreased by an estimated 1.63 points.

That may sound small, but spread across millions of children, even a 1–2 point shift means tens of thousands more potentially falling below thresholds for learning disabilities and developmental support. 

And IQ isn’t the only concern…

Fluoride overexposure has been linked to thyroid problems as well as joint and bone damage at higher concentrations. Plus, dental fluorosis—the white or brown staining of tooth enamel—now affects an estimated 65% of U.S. adolescents. So, it’s no coincidence, for example, that fluoride-free toothpaste is one of the fastest-growing segments in oral care.

According to the CDC, roughly 72.4% of the U.S. population served by community water systems drinks fluoridated tap water. Meanwhile, in Europe, 97% of countries do not fluoridate their water the way we do.

Think about that.

Remember Julia Roberts in Erin Brockovich? The movie that exposed a small town’s drinking water being poisoned by a massive utility company? That story was based on real events, and the chemical at the center of it was hexavalent chromium.

The International Agency for Research on Cancer classifies hexavalent chromium as a Group 1 carcinogen—meaning there is sufficient evidence that it causes cancer in humans. 

Ingestion has been linked to stomach and intestinal cancers. Studies of communities exposed through contaminated drinking water have found dramatically elevated rates of liver and kidney cancer. And beyond cancer, chromium-6 can cause liver toxicity, kidney damage, gastrointestinal ulcers, and reproductive harm.

Yet more than two decades later, there’s still no federal drinking water standard dedicated solely to chromium-6.

The only federal limit covers “total chromium”—which lumps the harmless form (chromium-3) together with the carcinogenic form (chromium-6). It’s like blending spoiled milk with fresh milk and calling the mixture “safe to drink.”

In 2024, California became the first state to set its own standard for chromium-6 at 10 ppb—ten times stricter than the federal total chromium limit. The Golden State decided waiting for the federal government wasn’t worth the risk. But if you don’t live in California, you may have no protection at all. 

After all, standard carbon-based filters weren’t designed to target hexavalent chromium either.

They’re called “forever chemicals” because once they enter your body, they don’t leave… 

Worse, they’ve been linked to cancer, thyroid disease, immune suppression, reproductive harm, and developmental delays in children.  And according to the Environmental Working Group, 158 million Americans—nearly half the country—could be drinking PFAS-contaminated water right now.

Enforceable limits for two PFAS were set in 2024, but the compliance deadline has already been pushed back. Four other PFAS chemicals had their limits rolled back entirely. That means these chemicals are unregulated, again.

Independent testing has shown that most mainstream carbon pitcher filters fail to meaningfully reduce PFAS levels. The chemicals are simply too small and too stable for basic carbon to catch.

The federal limit for nitrates in drinking water was set at 10 mg/L more than three decades ago, and regulators haven’t touched it since.

The science, on the other hand, has evolved dramatically… 

In June 2025, a study published in PLOS Water found that nitrate levels as low as 0.1 mg/L—just 1% of the legal limit—were associated with a 9% increase in preterm birth risk.

Let that sink in. One percent of the “safe” limit… 

Lead author Jason Semprini of Des Moines University was blunt: “There is no safe level of prenatal nitrate exposure.”

Climate change is compounding the problem. Nitrates come from fertilizer and animal waste on farmland. When intense rainstorms hit—storms that are growing more frequent—all that runoff washes directly into rivers and reservoirs. What used to stay in the fields may now be flowing straight to your tap.

Carbon filters don’t filter nitrates. Period.

We’ve known lead is dangerous for decades, so why is it still a problem?

In 2024, every water utility in America was required to submit a complete inventory of their service lines under the Lead and Copper Rule Improvements (LCRI). The goal was to identify and replace all lead pipes within 10 years. However, compliance plans aren’t due until 2027, and replacements could stretch into the 2030s. That likely means lead won’t be out of our water anytime soon. 

This is concerning for all of us since lead exposure has been linked to high blood pressure, heart disease, kidney damage, and memory loss. But, it’s particularly concerning for our children. Research shows that children’s IQ dropped by nearly 7 points as blood lead concentration increased—with the sharpest drop at the lowest levels of exposure. This suggests no amount of lead exposure is safe for them.

To make matters even worse, more than 20 million service lines nationwide came back classified as “unknown material.” Until those lines are dug up and inspected, who knows what they’re delivering with our water. 

Some carbon filters claim to “reduce” lead. And some do, to a degree. But “reduce” and “remove” are two very different things.

Every contaminant on this list can pose a serious, well-documented threat to your health. And mainstream carbon filters weren’t built to fully stop any of them.

Clearly Filtered, on the other hand, was.

Powered by our advanced Affinity® Filtration Technology, our best-selling Filtered Water Pitcher targets up to 365+ contaminants—including fluoride, lead, PFAS, hexavalent chromium, lithium, manganese, microplastics, and nitrates. And unlike mainstream filters, our systems clean your water without stripping out the healthy minerals your body wants, like calcium, potassium, and magnesium.

From our Filtered Water Pitcher to our Water Bottle, Inline Fridge Filter, and 3-Stage Under-the-Sink System, every product in our line is engineered to go far beyond what carbon can do alone.

Click here to learn more about each.