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Is Your Water Filter Actually Working? Here's How To Find Out
You run tap water through a filter every day and figure the boxes are checked: chlorine taste gone, mystery particles handled, and microplastics removed. But not all filters are equal.
Depending on the type of filter you use, potentially harmful contaminants like lead, PFAS, arsenic, and pesticides could still be making it into your glass.
That's where ROSE Water comes in: a new at-home test designed to help you understand what's actually in your drinking water, even after it's been filtered.
Why having a filter doesn't mean you're covered
Water filters are certified to do specific jobs, not remove every potentially harmful contaminant. According to NSF, an organization that develops independent testing standards for filtration systems, NSF/ANSI 42 certification focuses on improving the taste, smell, and appearance of water—not reducing contaminants that pose health risks.
For that, you'll want to look for filters certified under NSF/ANSI 53 or NSF/ANSI 58 (for reverse osmosis systems). These standards address contaminants with potential health effects, though the specific substances a filter is certified to reduce can vary.
In other words, just because your water tastes cleaner doesn't mean it's free of contaminants like lead, arsenic, or PFAS. And unless you know what your filter is certified to remove, you might not be getting the protection you think you are.
What's actually at stake
According to the Environmental Protection Agency (EPA)1, there's no safe level of lead exposure—which is why the agency's health-based goal for lead in drinking water is zero. Yet one study found2 that 25% of tap water sources tested exceeded 1 part per billion of lead, the reference level recommended by the American Academy of Pediatrics.
PFAS, also known as "forever chemicals," have been linked to higher cholesterol, liver damage, thyroid disease, and reproductive health concerns. And they're widespread: One study3 estimated that 71 million to 95 million Americans may rely on groundwater containing detectable PFAS.
Introducing ROSE, the exposure-health startup launching October 14, 2026
Co-founded by Eli Bronner and Henry Ellis, ROSE bills itself as the first exposure health company, backed by a scientific advisory board with expertise in environmental health, toxicology, epidemiology, and chemistry.
Its $399 at-home water test analyzes a single tap water sample for more than 100 contaminants, including PFAS, pesticides, heavy metals, and volatile organic compounds (VOCs). Samples are processed in an ISO-certified laboratory using advanced testing methods that the company says exceed standard EPA performance criteria. There's also a two-tap bundle for testing water from different sources in your home.
The company's approach is simple: "Test. Treat. Track." Rather than guessing what your water filter needs to remove, you can identify potential contaminants, take steps to address them, and retest to see whether those changes worked.
How the test actually works
Despite the clinical-looking kit, the testing process is surprisingly simple. Just freeze the included ice pack the night before, then collect your water sample in the morning (ideally after your tap has gone unused for about eight hours). The entire process takes roughly seven minutes.
Once you've collected your sample, drop it off at UPS the same day, preferably Monday through Wednesday to avoid weekend shipping delays. Your results arrive by email, and the ROSE team is available to walk you through the findings and answer any questions.
Turning your results into an actual plan
Knowing what's in your water also makes it easier to choose the right filter. For example, if your ROSE results detect lead or PFAS, you'll know to look for a filter certified under NSF/ANSI 53 or 58 to reduce those specific contaminants.
Of course, your filter might be up to the task—but it's just time for a replacement. Retesting is a great way to understand if your replacement cycle is too long, as most replacement recommendations are based on averages versus your local water source.
What's more, ROSE's water test is just the beginning. The company plans to expand into biomarker-based exposure testing in early 2027, with longer-term plans for air, mold, and body-based testing as part of a broader exposure-health platform.
The takeaway
Just because your water looks and tastes clean doesn't mean it's free of potentially harmful contaminants. Launched today, the ROSE Water Test takes the guesswork out of filtration, helping you understand what's actually in your tap water so you can make informed decisions about how to treat it. For $399, it's a way to get a clearer picture of your water quality—and whether your current filter is doing enough.