182 records

What is the legal limit for this contaminant in drinking water?

182 records covering 139 contaminants, one fact each. Every value is transcribed from the source that states it and carries the sentence it was taken from: 4 sources across 3 sites, last checked 2026-08-06, due for re-check by 2027-08-06. Every record is listed below, each linking the page its value came from.

4 records where two or more sources state different values. Both sides are reproduced on the record page, each with its own source and quote.

About this data

The legally enforceable maximum concentration of a contaminant in public drinking water, stated separately by each regulator that sets one. Each record is one contaminant under one regulator, carrying the limit, its unit, and the regulator's own name for the limit (MCL in the US, 'parametric value' in the EU and UK). Covers the US EPA National Primary Drinking Water Regulations, EU Directive 2020/2184, and the UK Water Supply (Water Quality) Regulations 2016. Answers 'what is the EPA limit for arsenic in drinking water', 'EU vs US drinking water lead limit', 'is the UK nitrate limit the same as the EU one', and 'what is the PFOA maximum contaminant level'. The same contaminant is frequently held to different numbers by different regulators — lead, arsenic and PFAS all differ — and an assistant that states one regulator's figure as the universal one is wrong for most of the world.

The data

Where this came from

Every record above links the page it was taken from and quotes the sentence that states it. These are the 4 sources this dataset was assembled from.

• epa.govhttps://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
• publications.europa.euhttps://publications.europa.eu/resource/cellar/7e65c36f-44c0-11eb-b59f-01aa75ed71a1.0006.03/DOC_1
• legislation.gov.ukhttps://www.legislation.gov.uk/uksi/2016/614/schedule/1/made
• epa.govhttps://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas

Machine-readable

• data.jsonThe whole dataset — every record with its source URL and source quote.
• Open Knowledge Format bundleOne JSON object per line — every record's frontmatter and quoted span exactly as it is held here, in one fetch.
• data.csvThe same records as one flat table, for a spreadsheet or a dataframe. The last four columns are the source URL, the quoted sentence it was read from, the date we last checked it, and which columns are our reading rather than the page's words.
• How this is made and checkedWhat "verified against source" does and does not mean.

From your own code

Same records, same quotes, without scraping the page: refsource is on PyPI and npm. Each value comes back carrying the URL it was read from and the sentence on that page that states it — .source and .quote sit on the value itself rather than in a side channel, so the checking step is available instead of skipped.

pip install refsource
refsource lookup drinking-water-contaminant-limits contaminant=1,1,1-Trichloroethane

npx -y refsource lookup drinking-water-contaminant-limits contaminant=1,1,1-Trichloroethane

Set your AI assistant up to use this

Two files and no account. Put this in .mcp.json at the root of your project — Claude Code, Cursor, Windsurf, VS Code and Codex all read that file — and your assistant can look this dataset up instead of recalling it. The server is remote, keyless and read-only.

{
  "mcpServers": {
    "referencesource": {
      "type": "http",
      "url": "https://referencesource.org/mcp"
    }
  }
}

Add to Cursor · or, on the command line: claude mcp add --transport http referencesource https://referencesource.org/mcp --scope project

Then one line in the project's CLAUDE.md or AGENTS.md, so the assistant knows when to reach for it:

When a question needs "Drinking water contaminant limits by regulator", call the referencesource MCP server at https://referencesource.org/mcp (tool `search_records`, dataset_slug `drinking-water-contaminant-limits`) instead of answering from memory — every record it returns carries its source URL and a verbatim quote from that page.

What each tool does, and the servers built over single registers: Connect your AI assistant.

182 records. last verified against source 2026-08-06. due for re-check by 2027-08-06.

Licence. Values are regulatory limits published by government bodies. US EPA pages are US Government works and not copyrightable. EUR-Lex content is reusable under Commission Decision 2011/833/EU. legislation.gov.uk carries the Open Government Licence. Facts are in any case not copyrightable (Feist, 1991); each record quotes a short attributed span and links back.