Lead
A neurotoxic metal that almost never originates in source water. Lead in tap water comes from lead pipes, lead solder and brass fittings between the main and the tap, which is why it is one of the few contaminants where the building matters more than the supply.
Key facts
- Contaminant group
- Metal
- World Health Organization — guideline
- 10 µg/lDesignated provisional because it is set by treatment feasibility rather than by a safe threshold.
- European Union — legal limit
- 5 µg/lReduced from 10 µg/l by the recast Drinking Water Directive, with a transition period.
- United Kingdom — legal limit
- 10 µg/lMeasured at the consumer tap.
- United States — action level
- 15 µg/lNot a health limit. It is a 90th-percentile trigger for corrosion control action across a system, and is frequently misreported as a safety standard.
Where it comes from
- Lead communication pipes and internal plumbing, widespread in housing built before about 1970 in the UK and before 1986 in the United States
- Lead-tin solder used on copper pipe joints
- Brass taps, valves and fittings, which may contain several percent lead
- Very rarely, industrial contamination or mining runoff in source water
How it behaves in water
Lead dissolves from pipe surfaces into standing water, so concentration rises the longer water sits still. It is far more aggressive in soft, acidic, low-alkalinity water, which is why lead exposure varies enormously between supply areas with identical pipework. Water companies dose orthophosphate to form a protective lead phosphate film inside pipes — a mitigation, not a removal.
How it is measured
Measured in micrograms per litre. The sampling protocol dominates the result: a fully flushed sample, a random daytime sample and a first-draw sample after overnight stagnation can differ several-fold from the same tap. Regulatory sampling in England and Wales uses random daytime sampling at the consumer tap.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | 10 µg/l | guideline | Designated provisional because it is set by treatment feasibility rather than by a safe threshold. |
| European Union | 5 µg/l | legal limit | Reduced from 10 µg/l by the recast Drinking Water Directive, with a transition period. |
| United Kingdom | 10 µg/l | legal limit | Measured at the consumer tap. |
| United States | 15 µg/l | action level | Not a health limit. It is a 90th-percentile trigger for corrosion control action across a system, and is frequently misreported as a safety standard. |
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
No level of lead exposure is known to be without effect. The principal concern is impaired neurological development in infants and young children, and the effect is on population-level outcomes rather than being individually detectable. This is why regulators pursue removal of lead pipework rather than treating a threshold as safe.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Replacing lead pipework — the only permanent solution | Boiling, which concentrates lead rather than removing it |
| 2 | Reverse osmosis certified to NSF/ANSI 58 for lead | Standard jug filters not specifically certified for lead |
| 3 | Activated carbon blocks specifically certified to NSF/ANSI 53 for lead reduction | Sediment filters |
| 4 | Distillation | Water softeners, which can make plumbosolvency worse by lowering hardness |
| 5 | Orthophosphate dosing by the water company, which suppresses but does not remove | — |
Occurrence
Exceedances in developed countries are typically localised to individual properties with lead plumbing rather than distributed across a supply zone.
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