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Lead in Drinking Water
Purpose
This Policy Position Statement presents a balanced technical view on the complex subject of Lead in Drinking Water, recognising both the significance of public health implications and the enormity of the potential costs involved with further actions to reduce lead concentrations, and encouraging solutions that are environmentally sustainable.
CIWEM’s Position on Lead in Drinking Water:
1. New European standards for lead in drinking water are fully justified to protect public health. The current interim standard of 25 µg/l will be tightened to 10 µg/l in 2013, providing a greater margin of safety. These standards apply at consumers’ taps.
2. Problems with sampling for determining compliance need to be more clearly understood and the specification of a harmonised sampling methodology by the European Commission is long over-due.
3. Wholesale replacement of lead pipes in the UK would involve great cost and inconvenience and is complicated by lead pipes being partly owned by the water supplier and partly owned by the property owner. Nevertheless, replacement of all lead pipes must be the long-term aim. In the meantime, a statutory replacement programme for lead pipes in public buildings and the opportunistic replacement of their lead connection pipes by water suppliers is recommended.
4. Reducing the plumbosolvency of water supplies (how readily they dissolve lead) by dosing with a corrosion inhibitor (most commonly ortho phosphate) can, depending on circumstances, offer a rapid, comprehensive and low-cost approach for achieving substantial compliance with both new lead standards.
5. Optimisation of plumbosolvency control by treatment requires: (i) correct pH conditions, (ii) correct ortho phosphate dose, (iii) adequate organics removal (particularly colour) and (iv) distribution networks to be free of significant iron discolouration problems.
6. In wastewater catchments where ortho phosphate dosing of water supplies is practised, an objective assessment of its environmental impact should be considered, to ensure that any subsequent environmental controls are justified.
7. Corrective action will depend on local circumstances and economics, and must be balanced with environmental impact. Whichever corrective action is taken, the intention must be to protect public health, regardless of any complications arising from the split ownership of lead pipes.
8. Across Europe there is scope for a better understanding of the complex inter-related issues relating to lead in drinking water, particularly because some Member States have not historically sampled from consumers’ premises and have little relevant data. Planned pan-UK and pan-European demonstration studies are strongly endorsed.
The Chartered Institution of Water and Environmental Management (CIWEM) is the leading professional body for the people who plan, protect and care for the environment and its resources, providing educational opportunities, independent information to the public and advice to government. Members in 96 countries include scientists, engineers, ecologists and students.
Context
Lead is a cumulative poison that affects the nervous system and can retard some aspects of child development (both size and intelligence). Lead pipes were used up to the 1980s both for connecting a property to the water supply main and for internal plumbing, due to lead’s strength, malleable nature and resistance to corrosion. In the UK, about 40% of properties are supplied via a lead pipe. Elsewhere in Europe, the estimated percentage of properties supplied by lead pipe-work varies from <5 to 50 per cent.
Although the rate of corrosion of the internal lead pipe wall is very small, lead dissolution into drinking water can very occasionally still reach concentrations of several milligrams per litre (parts per million), way in excess of the concentrations considered to be safe for regular ingestion (parts per billion). Lead pipes are, by far, the commonest source of lead in drinking water. There is no lead in the water suppliers’ distribution network, as the materials used for water mains are iron, plastic or asbestos cement. Short-term contributions are possible from some pipe-work fittings (particularly brass) and from the galvanic (electro-chemical) corrosion of lead-containing solders (which are now prohibited) used to join copper pipes. The lead that dissolves mostly remains in solution but contact with iron corrosion deposits from old iron mains can result in the lead being converted to a particulate form.
As the extent of the problem of lead in drinking water has become clearer, standards for drinking water have been tightened and much attention is being given to the recently implemented standards that derive from the European Drinking Water Directive of 1998. Such standards do not differentiate between the soluble and particulate forms of lead.
A standard of 25 µg/l has applied since December 2003 at the point of use by the consumer (commonly regarded as the kitchen sink tap). Although this standard is expressed as a weekly average concentration, it has been implemented more stringently in the UK as a maximum concentration because of the way compliance samples are obtained (through random day time samples of the first litre of water that issues from the tap when the sampler visits, taken from randomly selected properties). This standard tightens to 10 µg/l in December 2013 although the UK Government has already required some corrective measures to be taken in an attempt to achieve the tighter standard much sooner, as far as it is practicable to do so.
Key Issues
A Europe-wide problem
The concentration of lead in drinking water varies quite considerably, as a function of how much lead pipe is present, water-pipe contact time and the corrosivity of the water, making it difficult to characterise by sampling. This has made the optimisation of corrective measures much more difficult and many water suppliers have used additional investigational tools, including testing the corrosivity of the water, lead solubility modelling and computer simulation of lead emissions across whole zones (using probabilistic techniques). The UK has a comprehensive understanding of the extent of lead in drinking water problems as a result of widespread sampling at consumers’ taps for over fifteen years. In contrast, many other European countries have very little knowledge of the extent of the problem because they have not routinely monitored consumers’ premises. Such monitoring is a new legal requirement (from December 2003) that derives from the new 1998 Drinking Water Directive and it is to be expected that the full extent of the problem in some European countries will emerge over the next few years.
Pipe replacement?
The ultimate solution to the lead in drinking water problem would, very simply, be to replace all the lead pipes (water suppliers and property owners), but this is not without a range of problems:
• consumers do not perceive lead in drinking water to be a problem (you can’t see it, taste it or smell it) so are therefore reluctant to take expensive (and disruptive) action themselves, but they can take other measures to reduce exposure such as flushing standing water from the pipework after a period of non-use
• in many cases, the ownership of the lead piping is split between the water supplier and the property owner, complicating legal aspects
• the cost of replacing lead pipes is high – for example, the cost of replacing all lead pipes in the UK has been estimated at between Ł8 and Ł10 billion
• the density of properties with lead piping can be as high as 75% in many towns and cities, and any concerted replacement programme would cause considerable disruption to road users and property owners
• a question also arises: is it acceptable to simply leave old lead pipes in the ground or should they be removed and disposed of properly?
The long-term aim must be to replace all lead pipes. However, it will be necessary to recognise the deep reluctance of many property owners to replace their pipes (due to the inherent cost, disruption and inconvenience). It is suggested that replacement of lead pipes in buildings used by the public should be enforced by regulations, albeit over a realistic timescale. In appropriate circumstances, grant aid may need to be available.
Where replacement is preferred as the strategic means for achieving compliance, benefits will be limited if a water supplier replaces its part of the lead connection pipe but the property owner does not replace his/her part of the connection pipe and internal plumbing. However, the opportunistic replacement of lead connection pipes should be encouraged for example during mains refurbishment programmes. Water suppliers should continue to take active steps in their area to prevent the use by plumbers of lead-containing solders.
Phosphate dosing
An alternative preventative approach is to reduce the plumbosolvency of the water supplies. For low alkalinity supplies (<50 mg/l as CaCO3) much can be achieved by increasing the pH to above 8.0 but UK experience has shown that the dosing of ortho phosphate (a corrosion inhibitor) in the typical range 0.5 to 1.0 mg/l P is also required if the new European standards are to be achieved to a substantial degree. High alkalinity waters do not respond to pH elevation and plumbosolvency reductions are achieved by ortho phosphate dosing alone, albeit at a higher dose (typically 1.0 to 1.5 mg/l P).
Ortho phosphate dosing must be optimised in order to achieve -substantial compliance with the tighter standard of 10 µg/l whilst minimising environmental impacts of the additional ortho phosphate on receiving waters. Such optimisation is not straightforward because of the limitations inherent in sampling and additional techniques should be considered (such as corrosivity testing, solubility modelling and zonal emission modelling). Optimisation of ortho phosphate dosing is largely concerned with establishing the correct concentration, complicated by changing seasonal requirements and by the fact that all water supply areas have their own specific requirements, as determined by how much lead piping is present and by the plumbosolvency of the supplies. Optimisation also requires the correct pH to be maintained, natural organic constituents of the water to be minimised and the distribution network to be kept free from iron discolouration problems.
The UK approach
In the UK corrective treatment has been promoted, as opposed to the widespread replacement of lead pipes, as an appropriate first stage of achieving the new European standards for lead in drinking water. In consequence, about 95% of UK’s water supplies are now dosed with ortho phosphate and it has become apparent that substantial compliance has been achieved with not only the interim standard of 25 µg/l but with the standard of 10 µg/l as well in many areas. The Government will assess the extent of compliance in the next few years and then consider, whether, and to what extent, a strategic programme of lead pipe replacement is needed to achieve compliance with the 10 µg/l standard .
Discussion
The UK’s widespread use of ortho phosphate is consistent with practice in the USA but contrasts to many other European countries where the dosing of ortho phosphate to water supplies is considered to be unacceptable on environmental grounds. The environmental concerns relate to the eutrophication of water bodies and the possible prolific growth of algae, some of which can be toxic. Whilst this linkage is of course possible, the overall perspective relating to the ortho phosphate dosing of water supplies appears to be missing. Whereas the concentration added to water supplies for the purpose of reducing plumbosolvency is most commonly about 1 mg/l P, the sewage derived from water use commonly has an ortho phosphate concentration of about 10 mg/l P, i.e. ten times as much, (this is derived mostly from human waste and to a lesser extent from detergents). Therefore ortho phosphate dosing of water supplies is not critical with respect to eutrophication and the European stance poses a number of questions:
• If eutrophication is such an important issue, why has it not been considered necessary to remove phosphate from treated sewage effluent for the great majority of sewage treatment works?
• In cases where nutrients are considered to be a problem (or a potential problem) why does existing European legislation require phosphate removal down to only 1 or 2 mg/l P (depending on size of works) when it is well known that the limiting concentration of phosphate is as low as 0.01 mg/l P?
It can be concluded that the environmental aspects of dosing phosphate to water supplies need to be properly balanced with the public health consequences of not taking comprehensive action to reduce plumbosolvency, at least in the short to medium term. Whichever corrective actions are taken, the intention must be to protect public health, regardless of any complications arising from the split ownership of lead pipes.
August 2005
Note: CIWEM Policy Position Statements (PPS) represents the Institution’s views on issues at a particular point in time. It is accepted that situations change as research provides new evidence. It should be understood, therefore, that CIWEM PPS’s are under constant review, that previously held views may alter and lead to revised PPS’s.
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