Editorial authority · evidence in context
Water intelligence, explained.
Research, explainers, and practical guides that connect public water evidence to the questions households actually ask.
Every article separates published evidence, interpretation, and what the record cannot establish.
Latest publication 2026-09-22
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Rankings & Research
Cities Where PFAS Exceeds the 2024 Federal Limit
Federal 2024 monitoring found PFOS above the new 4.0 ng/L limit in 665 monitored cities. Here is what the records show and how to read them.
Read the analysisRankings & Research
Cities Where Lead Exceeds the Federal Action Level
Federal monitoring recorded lead above the 15 µg/L action level in 26 cities. Here is what that number means, and what it does not.
Read articleProduct Comparisons
Best PFAS Water Filter Formats Compared (2026)
Pitcher, countertop, under-sink or whole-house? A plain comparison of the filter formats certified to reduce PFAS, and which situation each one fits.
Read articleProduct Comparisons
Best Lead Water Filter: Why It's a Plumbing Decision (2026)
Lead usually comes from your home's own pipes, not the utility. That changes which filter you need and where you put it. A plain comparison.
Read articleContaminants
Arsenic in Drinking Water: Where It Comes From and the Limit
Arsenic dissolves naturally into groundwater from rock and soil. Here's what the federal limit is, why it's set so low, and how to check and treat for it.
Read articleContaminants
Nitrate in Water: Wells, Infants, and the Federal Limit
Nitrate is one of the most common contaminants in farm country, and it carries a specific risk for infants. Here's the limit, why levels spike, and how to treat it.
Read articleTreatment Guides
How to Test Your Tap Water at Home
Your utility's record describes the water it delivers — not the water at your tap. Here's how to test your own address, what to test for, and how to read the result.
Read articleTreatment Guides
Do You Need a Water Softener? Reading Hardness and Options
Hard water is a comfort and plumbing issue, not a health one. Here's how to read your hardness number and decide whether a softener is actually worth it.
Read articleRegional Research
What Tucson's 2024 Water Data Actually Shows
Tucson Water serves 732,906 people from groundwater. Here's what the EPA's 2024 PFAS round and the latest lead monitoring actually recorded — and what's still pending.
Read articleRankings & Research
US Cities With the Highest Water Purity Scores (2024)
The cities at the top of our Purity Score ranking all sit at 100/100 — but a perfect score means something narrower than it sounds. Here's how to read the list.
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The Largest US Water Systems by Population Served
The systems serving the most Americans span a wide range of Purity Scores. Size isn't a quality signal — here's what the biggest US water utilities' records actually show.
Read articleWater Intelligence
How the PurityMap Purity Score Works
The Purity Score is one number from 0 to 100 — but only for the contaminants a system actually measured. Here's how it's built, and what it deliberately leaves out.
Read articleWater Intelligence
What a 'Non-Detect' Really Means on Your Water Report
A 'non-detect' is one of the most misread words on a water report. It does not mean zero — here is what it actually means.
Read articleProduct Comparisons
Reverse Osmosis vs. Carbon Filters: Which Removes What
The two most common home technologies work very differently. Here is a plain comparison so you buy for your actual problem.
Read articleTreatment Guides
Hard Water Explained: What the Grains Mean and When to Soften
Hard water is a plumbing and comfort issue, not a health one. Here is how to read hardness and decide whether a softener is worth it.
Read articleContaminants
Chlorine and TTHM: The Disinfection Trade-off
The disinfectant that keeps waterborne disease rare also creates by-products. Here's how to think about that balance instead of fearing it.
Read articleRankings & Research
The US Cities With the Lowest Water Purity Scores (2024)
What a low Purity Score does — and does not — tell you, and how to read our national rankings without drawing the wrong conclusion.
Read articleTreatment Guides
Choosing a Water Filter by Contaminant: PFAS, Lead & More
The right filter depends entirely on what you are trying to remove. Match the technology to your actual finding — not to marketing.
Read articleContaminants
Lead in Tap Water: How to Read the Numbers on Your Report
A system can report 'below the action level' and your kitchen tap can still have lead. Here is how lead reporting actually works and what to do about it.
Read articleWater Intelligence
PFAS in US Drinking Water: What the 2024 EPA Limits Mean
In 2024 the EPA set the first enforceable national limits on PFAS 'forever chemicals.' Here is what changed, why the limits are so low, and how to check your own city.
Read articleEditorial work stays connected to the record.
Journal analysis adds context; it does not replace a water-system report, source document, ranking methodology, or certified household test.