Contaminant
Nitrite
An intermediate in the nitrogen cycle, and considerably more acutely toxic than nitrate. Its presence in treated water usually indicates a problem in the distribution network rather than in the source.
Key facts
- Contaminant group
- Nutrient
- World Health Organization — guideline
- 3 mg/l as NO₂A short-term value of 0.2 mg/l applies for chronic exposure.
- European Union — legal limit
- 0.5 mg/l as NO₂A combined nitrate/nitrite formula also applies: [nitrate]/50 + [nitrite]/3 must not exceed 1.
- United Kingdom — legal limit
- 0.5 mg/l as NO₂
- United States — legal limit
- 1 mg/l as N
Where it comes from
- Incomplete nitrification or denitrification in soil and water
- Nitrification within chloraminated distribution networks where ammonia is over-dosed
- Sewage and industrial discharge
- Corrosion inhibitors in some industrial systems
How it behaves in water
Unstable, and rapidly oxidised to nitrate under aerobic conditions. Persistent nitrite in a treated supply is therefore a signal of active nitrification, not of source contamination.
How it is measured
Milligrams per litre, as nitrite ion or as nitrite-nitrogen. The same as-N versus as-ion trap applies as for nitrate.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | 3 mg/l as NO₂ | guideline | A short-term value of 0.2 mg/l applies for chronic exposure. |
| European Union | 0.5 mg/l as NO₂ | legal limit | A combined nitrate/nitrite formula also applies: [nitrate]/50 + [nitrite]/3 must not exceed 1. |
| United Kingdom | 0.5 mg/l as NO₂ | legal limit | — |
| United States | 1 mg/l as N | legal limit | — |
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
Oxidises haemoglobin to methaemoglobin, impairing oxygen transport. Roughly ten times more potent than nitrate on a molar basis, because nitrate must first be reduced to nitrite to have any effect. Infants under six months are the sensitive group.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Chlorination, which oxidises nitrite to nitrate | Boiling |
| 2 | Ion exchange | Activated carbon |
| 3 | Reverse osmosis | Sediment filtration |
| 4 | Correcting the ammonia dose where nitrification is occurring in the network | — |
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