Updated April 2026 · EPA SDWIS data
Drinking Water Safety Guides
Long-form, data-driven guides to U.S. drinking water — how to check your tap, what each contaminant actually does, which filter technology removes what, and how the regulatory framework around the Safe Drinking Water Act fits together. Every guide is built from public EPA SDWIS data and the EWG Tap Water Database, with no manufacturer or utility sponsorship.
Why Drinking Water Reporting Is Confusing
U.S. drinking water is governed by a layered system. The Safe Drinking Water Act sets federal limits — Maximum Contaminant Levels (MCLs) — for roughly 90 contaminants. State agencies enforce those rules under EPA-granted "primacy," which means actual oversight quality varies state to state. Utilities publish annual Consumer Confidence Reports each July listing what they detected, but those reports are written for compliance, not consumer comprehension. EPA's SDWIS database records violations and enforcement actions, but the underlying schema requires interpretation. And below all of that, lead service lines and household plumbing can introduce contaminants downstream of any utility-side reading.
These guides translate that system into something usable. They explain what the EPA MCL is and is not, which violations matter most for health, what the gap is between an MCL and a health-based goal (MCLG), and how to read a CCR without a chemistry background.
Browse Guides by Topic
Getting Started
Reference content on a specific corner of U.S. drinking water safety, written from public EPA, USGS, and HHS data sources with no manufacturer or utility sponsorship.
Contaminants
Per-contaminant deep dives — lead, PFAS, nitrates, arsenic, disinfection byproducts — with the EPA Maximum Contaminant Level, the non-enforceable health-based goal, common sources, and which treatment technologies are effective.
Solutions
Reference content on a specific corner of U.S. drinking water safety, written from public EPA, USGS, and HHS data sources with no manufacturer or utility sponsorship.
How These Guides Are Researched
Every contaminant level, violation count, and enforcement action in these guides traces back to a public federal dataset. Violations and enforcement come from the EPA Safe Drinking Water Information System. Contaminant MCLs and MCLGs come from EPA's National Primary Drinking Water Regulations. Filter technology context cites NSF/ANSI standards. Each guide ends with the source list and a refresh date so claims are auditable. Read the full IsWaterSafe methodology for how the score and rankings are computed.
IsWaterSafe is not medical or health advice. Guides describe what the EPA data shows; they do not diagnose a specific health problem, prescribe treatment, or rule out concerns specific to your household. Detection of a contaminant above an EPA MCL is a regulatory event, not a clinical claim. If you have a specific concern (a private well, an immunocompromised household member, a pregnancy, an infant on tap-water formula, a recent lead exposure), talk to your physician and contact your local public health department.
Frequently Asked Questions
How do I find out what's in my tap water?
Three sources, in order. First, your utility's Consumer Confidence Report (CCR), which the Safe Drinking Water Act requires every community water system to publish by July 1 each year — it lists every regulated contaminant detected and how the level compared to the EPA Maximum Contaminant Level. Second, the EPA Safe Drinking Water Information System (SDWIS) federal reporting database, which records violations and enforcement history. Third, an NSF-certified at-home test kit if you want a reading specific to your address (which captures plumbing-side contamination invisible to utility reports). The "How to Check Your Tap Water" guide walks through all three.
Are EPA limits the same as "safe"?
No. The EPA Maximum Contaminant Level (MCL) is the legally enforceable limit under the Safe Drinking Water Act — exceeding it is a violation. EPA also publishes Maximum Contaminant Level Goals (MCLGs), which are non-enforceable health-based targets. For lead, PFAS PFOA, PFAS PFOS, and several other contaminants, the MCLG is zero. The MCL is set as low as feasible given treatment technology and cost; the MCLG reflects what EPA considers a level "below which there are no known or expected health risks." Both are published per contaminant in the EPA primary drinking water regulations.
What is PFAS and which systems are affected?
PFAS — per- and polyfluoroalkyl substances — are a family of thousands of synthetic chemicals used since the 1940s in nonstick cookware, firefighting foam, stain-resistant fabrics, and many industrial processes. They are persistent ("forever chemicals"), bioaccumulative, and increasingly detected in U.S. drinking water. In April 2024 EPA finalized the first National Primary Drinking Water Regulation for six PFAS, including PFOA and PFOS at 4 parts per trillion. Compliance monitoring began in 2027. The PFAS guide tracks which systems have detections and which are above the new MCLs.
Will a Brita-style pitcher remove lead and PFAS?
Standard activated-carbon pitchers reduce some contaminants but are not certified for lead or PFAS removal in most cases. NSF/ANSI standards 53 (lead) and 401/P473 (PFAS) certify products that have been independently tested for those specific reductions. The filter guide explains which technology removes what — activated carbon for chlorine, taste, and many organics; reverse osmosis or distillation for lead, nitrates, arsenic, and PFAS; ion exchange for hard-water minerals — and links to NSF's certified-product database.
Where does IsWaterSafe get its numbers?
Every violation, contaminant detection, and enforcement action on IsWaterSafe traces to the EPA Safe Drinking Water Information System (SDWIS), the federal reporting database under the Safe Drinking Water Act. Contaminant context (sources, MCLs, MCLGs, treatment options) comes from EPA's primary drinking water regulations and the EWG Tap Water Database. The IsWaterSafe dataset was last refreshed April 2026.
Sources: EPA Safe Drinking Water Information System (SDWIS), EPA National Primary Drinking Water Regulations, EWG Tap Water Database, NSF/ANSI drinking water treatment standards. SDWIS and EPA regulations are U.S. government public domain. Cite as: "IsWaterSafe, April 2026 reading. Data: EPA SDWIS."
Last updated 2026-04-04 · 3 guides published.