Guides

The score is two EPA records folded into one number. What the air half and the water half each measure, why a single number can hide more than it shows, and how to read the breakdown underneath it.

A side-by-side score is easy to misread as a verdict. What actually drives a gap between two ZIP codes, when the composite number is the wrong thing to compare, and a short checklist for using the comparison tool well.

Your Consumer Confidence Report and this site's utility lookup draw from the same federal system but answer different questions. What a CCR tells you, what SDWIS/ECHO adds, and how to find your own utility if you're not sure which one serves you.

A state air ranking is only as complete as its monitors, and about half of US counties have none. What population-weighting does and doesn't fix, and how to tell whether your own county is even in the sample.

Not every violation on a utility's record means someone drank contaminated water. The difference between a health-based violation and a monitoring or reporting violation, why the site weights them differently, and how to read a violation count without over- or under-reacting to it.

A single national list of best and worst counties compresses two different scores, two different scales of coverage gaps, and thousands of counties into one rank. What the rank can tell you, what it can't, and why a close rank is not a meaningful difference.

A clean violation record means a utility met the legal limits EPA and your state test for — it does not mean every contaminant was tested for, or that the limits catch everything a resident might care about. What a clean record actually certifies, and what it leaves out.

A single year's AQI can be a fluke — a wildfire smoke season, an unusually calm year. How to tell a real multi-year trend from ordinary noise, and why this site compares complete years only rather than fitting a line through partial data.