Lead is one of the most studied environmental toxins in public health. For decades, concern focused mainly on obvious lead poisoning: severe symptoms, high blood lead concentrations and urgent medical treatment. Today, the evidence points to a more difficult problem. Lead can affect children’s brain development even at blood lead concentrations that may not cause visible symptoms.
That evidence is why the UK lowered the public health intervention concentration for lead exposure in children and pregnant women. The change reflects a wider scientific shift: lead exposure is not only a clinical poisoning issue. It is a prevention issue.
For older homes, including many properties across London, the practical question is simple: where could lead still be present, and how can exposure be reduced before it affects a child’s health?
Table of Contents
Key Facts
| Issue | What it means |
|---|---|
| There is no defined safe threshold for lead in children | Harm may occur even at low blood lead concentrations. |
| UK public health intervention concentration | Lowered from 10µg/dL to 5µg/dL for children under 16 and pregnant women. |
| Clinical investigation threshold | UKHSA states that 2–5µg/dL is widely accepted in the UK as a clinical threshold above which investigation should occur and a source should be identified. |
| Main exposure routes | Paint, dust, soil, drinking water from lead pipework, imported products, traditional remedies and take-home occupational exposure. |
| Older homes matter | Older housing is more likely to contain lead paint, contaminated dust, historic soil contamination and legacy lead water supply pipes. |
| Lead in water is a separate measurement | Blood lead is measured in µg/dL. Lead in drinking water is measured in µg/L. |
Why lead matters for children’s brain development
Children are especially vulnerable to lead because their brains and nervous systems are still developing. The unborn baby is also vulnerable because lead can cross the placental barrier. Public Health England’s 2021 review, Evaluation of whether to lower the public health intervention concentration for lead exposure in children, describes lead as a non-threshold contaminant. That means adverse health effects may occur at any level of exposure, rather than only above a clearly safe-or-unsafe cut-off.
The review found strong evidence for adverse effects on children’s cognitive function at blood lead concentrations below 5µg/dL, and evidence for externalising behaviours, attention and hyperactivity effects, and delayed sexual maturation or puberty onset below 10µg/dL.
The concern is not only severe poisoning. A child with low-level lead exposure may not look obviously unwell. The harm may appear as a small reduction in cognitive performance, attention, behaviour or educational attainment. At an individual level this can be difficult to detect. Across a population, however, even small average shifts in IQ can have major educational and social consequences.
What the IQ evidence shows
The link between lead exposure and IQ is one of the strongest reasons public health bodies have moved toward lower intervention levels.
Public Health England’s 2021 review cites evidence that IQ declines as blood lead concentration rises, with proportionally greater effects at lower exposure levels. One pooled analysis observed an estimated 6.2-point IQ decline as blood lead rose from below 1µg/dL to 10µg/dL, with greater associations at the lower end of exposure.
This point matters. It means the first increments of exposure may be more important than many people assume. The relationship is not simply that “high lead is dangerous” and “low lead is safe”. Instead, the evidence suggests there is no clearly defined safe threshold for children. The same review describes a supra-linear dose response for intelligence-related effects, without an identifiable lower threshold below which exposure does not result in adverse effects.
That is the central public-health argument. Lead exposure does not need to produce dramatic symptoms to cause harm. Prevention is more reliable than treatment after exposure has already occurred.
Why the UK lowered the intervention concentration
The official UK term is public health intervention concentration. This is the blood lead concentration at which public health teams become involved in case management.
Before 2021, the public health intervention concentration for children in England was 10µg/dL. Public Health England’s 2021 review recommended lowering the public health intervention concentration and surveillance case definition for children under 16 and pregnant women from ≥10µg/dL to ≥5µg/dL.
UKHSA’s current guidance states that public health teams in England are notified if a child under 16 has a blood lead concentration at or above 5µg/dL. For adults, public health notification is generally at or above 10µg/dL, unless the adult is pregnant.
| Blood lead concentration | What it means in practice |
|---|---|
| Below 2µg/dL | Lower exposure, but not proof of “zero risk”. |
| 2–5µg/dL | Investigation may be appropriate; UKHSA says a source should be identified. |
| 5µg/dL or above | Public health intervention concentration for children under 16 and pregnant women. |
| 10µg/dL or above | Public health action level for most other adults. |
The key point is that 5µg/dL is not a safe level. It is the level at which formal public health intervention is triggered for children and pregnant women. Below that level, the emphasis remains on primary prevention: reducing exposure before it becomes a case
Blood lead and lead in drinking water are measured differently
Two different measurements are often confused.
Blood lead concentration is measured in µg/dL, or micrograms per decilitre. This tells clinicians and public health teams about exposure in the person.
Lead in drinking water is measured in µg/L, or micrograms per litre. This tells water companies and regulators about the concentration of lead in water.
In England, the prescribed concentration value for lead in drinking water is 10µg/L. UKHSA guidance states that if drinking water is the suspected source, the water company should test the water, and that the local water company can test residential supplies for lead free of charge where drinking water is a possible source.
The two values are not directly interchangeable. A blood lead result shows exposure in a person. A water lead result helps identify whether drinking water may be one of the sources
How children are exposed to lead
Lead exposure can come from several routes, but in modern high-income countries the main concern for children is usually ingestion rather than inhalation. After the removal of lead from petrol, ingestion became the most common route of exposure in high-income countries, particularly through dust and flakes from old leaded paint. Children are at particular risk because normal hand-to-mouth behaviour can bring contaminated dust, soil or paint fragments into the body.
Public Health England’s 2021 review lists several continuing sources of lead exposure, including food, flaking or chipped lead paint, lead paint dust, contaminated soil, imported cookware, lead-glazed ceramics, antique or imported toys, imported spices, some traditional medicines and cosmetics, and drinking water where historic lead pipework, solder or fittings are present.
| Exposure route | How it happens | Why older housing matters |
|---|---|---|
| Lead paint and paint dust | Old painted surfaces chip, flake, peel or create dust during sanding, renovation or wear | Lead paint may remain beneath newer paint layers in older properties |
| House dust | Dust becomes contaminated by old paint, soil tracked indoors or renovation residue | Children ingest dust through normal hand-to-mouth behaviour |
| Soil | Historic lead from paint, petrol, industry or building materials remains in the ground | Children may ingest soil directly or through dust brought indoors |
| Drinking water | Water passes through lead pipes, lead solder or lead-containing fittings | Older properties are more likely to retain legacy supply pipes or plumbing |
| Imported products | Lead may be present in some toys, cosmetics, cookware, ceramics, spices or traditional remedies | This route is not housing-specific but can contribute to unexplained exposure |
| Take-home occupational or hobby exposure | Lead dust is brought home on clothing, shoes or tools | Relevant where household members work with construction, metalwork, shooting ranges, stained glass or similar activities |
Drinking water is not always the dominant source of lead exposure, but one England tap-water study found that it can account, on average, for about 1% to 20% of total lead burden, and substantially more where homes are served by lead plumbing.
This is why a lead investigation should not focus on one source too early. Drinking water can be important, especially where lead pipes remain, but paint, dust, soil, consumer products and family occupations can also matter. A good public health response looks for the exposure source and interrupts the pathway.
What recent UK surveillance shows
The latest UKHSA Lead Exposure in Children Surveillance System report shows that lead exposure in children remains a current issue in England.
In 2024, 247 cases were reported to UKHSA, a 9% increase from 2023. UKHSA also notes that reported cases are likely to be significantly lower than the estimated incidence of lead exposure in children in England. Among 2024 cases with completed enhanced surveillance questionnaires, the most commonly reported exposure sources were soil, paint and drinking-water pipes. Drinking-water pipes were reported in 12% of those questionnaire-based cases.
The same UKHSA report states that children with pica or hand-to-mouth behaviour in environments with lead hazards are at the highest risk, and it lists important sources including deteriorating leaded paint, consumer products, parental hobbies or occupations, lead water pipes, lead solder and contaminated soil or land.
This matters because lead exposure in children is rarely explained by one source alone. Recent UKHSA surveillance shows that soil, paint and drinking-water pipes all continue to appear in case investigations. Lead pipework is a serious exposure route, but in older homes it may sit alongside lead paint, contaminated dust and historic soil contamination.
What the Crabbe housing study adds
Once the main exposure routes are understood, the importance of older housing becomes clearer. Older homes are more likely to contain several possible lead sources at once: old paint layers, contaminated house dust, historic soil contamination and legacy water supply pipes.
A 2022 UKHSA-linked study by Crabbe and colleagues, published in BMC Public Health, is particularly useful because it looks specifically at England. The paper, “As safe as houses; the risk of childhood lead exposure from housing in England and implications for public health”, examined childhood lead exposure cases reported to UKHSA between 2014 and 2020 and explored the relationship between housing characteristics and elevated blood lead concentration.
The study found that, after adjustment for reporting source, housing age and housing type, cases living in housing built before 1976 had blood lead concentrations 0.32µmol/L higher, equivalent to about 6.63µg/dL, than cases living in housing built after 1976. It also found that cases were 1.68 times more likely to live in terraced housing than would be expected from the national housing-stock profile. The authors concluded that housing age and type may act as a proxy for lead exposure risk because older homes are more likely to contain leaded paint, lead water pipes and lead-contaminated dust from indoor and outdoor sources.
This does not mean every old house contains lead. It means older housing is a practical screening indicator. Where children or pregnant women live in older properties, especially terraced homes or buildings with older paint and plumbing, lead-source checks are a sensible precaution.
Drinking water, lead pipes and the London context
Lead is not usually present because of the water leaving treatment works. The main drinking-water risk comes when water passes through lead pipework, lead solder or lead-containing fittings.
A useful England-specific study by Jarvis and colleagues helps show what this can look like in practice. Using a duplicate-intake method in 23 properties and 48 individuals across 2 English water-company regions, the researchers asked participants to take a sub-sample from each drink consumed at home over 3 days in both winter and summer. The study found that drinking water contributes, on average, around 1% to 20% of total lead burden, but that exposure can be much higher in properties served by lead plumbing. Consumer exposure was highest in homes with lead service pipes supplied by water without phosphate dosing.
Across all duplicate water-intake samples, 7.4% in winter and 10.1% in summer exceeded 10µg/L. In the highest-risk homes, exceedance rates were much higher. In one study area, 38.8% of winter samples and 43.5% of summer samples from leaded, non-phosphate-dosed homes exceeded 10µg/L, and a maximum summer concentration of 1,050µg/L was recorded.
The Jarvis study is also important because it shows how variable real household exposure can be. Water lead concentrations were highly variable, summer concentrations were generally higher than winter concentrations, and the researchers did not find a consistent simple pattern in which the first drink of the day was always the highest. That matters because flushing can reduce standing-water exposure in some circumstances, but it is not a substitute for identifying and removing lead plumbing where it remains.
The study also used the IEUBK model to estimate possible blood lead impacts in children. Under the highest observed average water-lead scenario, 46% of children aged 0 to 7 were predicted to exceed 5µg/dL and 6% were predicted to exceed 10µg/dL. The authors were clear that the study was not designed to represent England as a whole, but it shows clearly that drinking water can be a material contributor to lead exposure in some homes.
The Drinking Water Inspectorate states that lead can dissolve into drinking water when water comes into contact with lead pipes. It identifies the main sources as communication pipes owned by water companies and supply pipes owned by consumers within their property. In 2024, there were 53 compliance sample failures for lead in England out of 13,394 samples analysed for lead. The Inspectorate also states that consumers are protected to a large extent by phosphate dosing, but that a wider national and company strategy is still needed to reduce exposure further.
Thames Water similarly states that its water mains are not made of lead and that there is virtually no lead in drinking water leaving its treatment works. However, some properties may still have a lead pipe feeding the property or lead in internal plumbing, and small amounts of lead may dissolve into the water in those cases. Thames Water says homes built after 1970, or homes where all pipework has been replaced since 1970, are unlikely to have lead pipes.
Responsibility is split. Thames Water says customers own the internal pipework and the supply pipe, while Thames Water owns the communication pipe from the water main to the outside stop valve.
That split is one of the reasons lead in drinking water is difficult to solve. Replacing only the water-company side may not remove all lead contact if the private supply pipe or internal plumbing still contains lead.
Thames Water’s long-term water quality strategy frames lead pipework as a public health risk that cannot be solved by water treatment alone. Its AMP8 plan proposes 54,000 lead communication pipe replacements and a customer-side trial to test education, support and practical approaches for removing customer-side lead supply pipes. The same strategy states that current chemical mitigation, including orthophosphate dosing, is reaching the limit of protection, and that removing lead pipework from the drinking-water route is the only long-term solution.
What older homes should check
For properties built before 1970, especially where young children or pregnant women live or regularly visit, the sensible approach is to identify whether lead is present and remove it where practical.
The first place to inspect is usually the pipe entering the property near the internal stop valve, often under the kitchen sink, behind kitchen cupboards or in a cupboard under the stairs. Thames Water advises checking the pipe leading to the internal stop valve and the pipe near the outside stop valve, and its scheme guidance explains that suspected lead pipework should be assessed and replaced where possible.
A visual check is useful, but it is not the same as a full assessment. If drinking water is suspected as a lead source, UKHSA says the water supply company should test the water.
Practical steps for older homes:
- Check the incoming water supply pipe near the internal stop valve.
- Check whether the private supply pipe is lead, especially in homes built before 1970.
- Contact the water supplier if drinking water is suspected as a lead source.
- Use a qualified plumber for replacement work.
- Avoid disturbing old paint layers without proper precautions, especially during sanding or renovation.
- Consider other routes, including soil, dust, imported products and occupational take-home exposure.
For confirmed lead pipework, replacement is the strongest long-term solution. Flushing the cold kitchen tap may reduce standing-water exposure in the short term, but it should not be treated as a permanent substitute for removing lead pipework where vulnerable people are present, especially because household exposure can vary considerably depending on plumbing conditions, season and how water is actually used. Thames Water recommends running the cold kitchen tap for two minutes in the morning or after time away as a short-term measure, while also warning against disturbing lead pipes
Reference list
- Public Health England. Evaluation of whether to lower the public health intervention concentration for lead exposure in children. A report by the lead intervention concentration working group. Published July 2021.
- UK Health Security Agency. Lead: environmental and public health intervention. Current guidance on blood lead intervention concentrations and investigation thresholds.
- UK Health Security Agency. Lead Exposure in Children Surveillance System annual report, 2025. Surveillance data for 2024, including reported cases and exposure routes.
- Crabbe, H., Verlander, N. Q., Iqbal, N., Close, R., White, G., Leonardi, G. S. and Busby, A. “As safe as houses; the risk of childhood lead exposure from housing in England and implications for public health.” BMC Public Health, 2022.
- Jarvis, P., Quy, K., Macadam, J., Edwards, M. and Smith, M. “Intake of lead (Pb) from tap water of homes with leaded and low lead plumbing systems.” Science of the Total Environment, 2018.
- Drinking Water Inspectorate. Lead in water. Summary of lead compliance sample failures and lead sources in drinking water, 2024.
- Thames Water. Lead. Customer guidance on lead in drinking water, lead pipe identification and short-term measures.
- Thames Water. Lead pipe replacement scheme. Guidance on customer-side supply pipes, Thames Water communication pipes and scheme criteria.
- Thames Water. TMS22 Enhancement Case: Long Term Water Quality Strategy Lead. AMP8 strategy for lead communication pipe replacement and customer-side trial
