Pesticides
A large and changing group of regulated substances. European drinking water regulation is unusual in setting a uniform limit per individual pesticide regardless of its toxicity — a deliberately precautionary policy choice rather than a health-derived threshold.
Key facts
- Contaminant group
- Agricultural
- European Union — legal limit
- 0.1 µg/l per pesticide; 0.5 µg/l totalSet by the precautionary principle and analytical capability, not by compound-specific toxicology. Many pesticides have health-based values far above 0.1 µg/l, and a few below it.
- United Kingdom — legal limit
- 0.1 µg/l per pesticide; 0.5 µg/l total
- World Health Organization — guideline
- Compound-specific guideline valuesWHO derives a separate value for each substance from its own toxicology, so its values differ greatly between compounds.
Where it comes from
- Agricultural application and subsequent leaching or runoff
- Amenity and highway weed control
- Historic legacy compounds persisting in groundwater decades after withdrawal
How it behaves in water
Mobility and persistence vary enormously between compounds. Some, such as certain triazine metabolites, remain detectable in aquifers long after the parent compound was banned.
How it is measured
Measured in micrograms per litre, with analytical suites covering hundreds of compounds. A "pesticides not detected" result is only as broad as the analyte list used.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| European Union | 0.1 µg/l per pesticide; 0.5 µg/l total | legal limit | Set by the precautionary principle and analytical capability, not by compound-specific toxicology. Many pesticides have health-based values far above 0.1 µg/l, and a few below it. |
| United Kingdom | 0.1 µg/l per pesticide; 0.5 µg/l total | legal limit | — |
| World Health Organization | Compound-specific guideline values | guideline | WHO derives a separate value for each substance from its own toxicology, so its values differ greatly between compounds. |
Table sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- European Commission — Drinking Water Directive (EU) 2020/2184 and reporting. Open — attribution required · European Commission reuse policy (Decision 2011/833/EU)
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- United States Environmental Protection Agency — Safe Drinking Water Information System. Open · US Government work — public domain
Health context
Because the European limit is not health-derived, an exceedance is a regulatory failure and a signal of catchment pressure, but does not by itself imply a health risk. Conversely, compliance does not imply that every compound present has been assessed.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Granular and powdered activated carbon, the mainstay | Boiling |
| 2 | Ozone combined with carbon | Sediment filtration |
| 3 | Reverse osmosis and nanofiltration | Chlorination, which can transform but not remove some compounds |
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Peer-reviewed scientific literature — Open-access hydrology, water chemistry and water use research. Public but restricted · Publisher terms — public access, reuse not clearly granted