Phosphate
Not a drinking water health concern, and the most important single pollutant in fresh water. Phosphorus is usually the nutrient limiting algal growth, so it is the one that determines whether a lake or river eutrophies.
Key facts
- Contaminant group
- Nutrient
- European Union — guideline
- No drinking water limitRegulated as an environmental quality standard for surface waters under the Water Framework Directive, not as a drinking water parameter.
- United Kingdom — legal limit
- Environmental standards vary by water body typeTypical good-status targets for lowland rivers are in the range 0.05–0.12 mg/l as P.
Where it comes from
- Wastewater treatment works effluent — historically the largest point source
- Agricultural fertiliser and manure, carried on eroded soil particles
- Detergents, now much reduced by phosphate restrictions
- Orthophosphate deliberately dosed into drinking water for lead control
- Release from lake sediment under anoxic conditions
How it behaves in water
Binds strongly to soil particles, so it travels with sediment rather than in solution. That makes erosion control the primary route to reducing it, and it also means phosphorus accumulated in sediment keeps releasing for years after external inputs stop.
How it is measured
Reported as orthophosphate, total phosphorus or soluble reactive phosphorus, in milligrams per litre as P or as PO₄. The three are different quantities and the conversion between as-P and as-PO₄ is a factor of 3.07.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| European Union | No drinking water limit | guideline | Regulated as an environmental quality standard for surface waters under the Water Framework Directive, not as a drinking water parameter. |
| United Kingdom | Environmental standards vary by water body type | legal limit | Typical good-status targets for lowland rivers are in the range 0.05–0.12 mg/l as P. |
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
Phosphate is an essential nutrient with no drinking water health concern at any plausible concentration. Its significance is entirely ecological.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Chemical precipitation with iron or aluminium salts at wastewater works | Anything applied at the tap — this is a catchment and wastewater problem, not a drinking water one |
| 2 | Biological phosphorus removal | — |
| 3 | Constructed wetlands | — |
| 4 | Catchment erosion control, which addresses the source rather than the symptom | — |
Occurrence
Phosphorus stripping at wastewater works has substantially reduced point-source loading across Europe. Diffuse agricultural loading has not fallen comparably, and is now the dominant source in most catchments.
Relationships
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