Drinking water: treatment with orthophosphates reduces the concentration of lead in the water supply but more knowledge is needed about its effects

The presence of lead in drinking water essentially comes from the constituent materials of the distribution network, made from or containing lead. It mainly concerns public connections located between the main pipes and the water meter, and indoor pipes, especially in older housing. The adverse health effects in humans are correlated with lead concentrations in blood, and the clinical signs are sometimes non-specific and erratic. Lead poisoning, meaning acute or chronic lead intoxication, is more frequent and severe in young children. According to the infant total diet study published by ANSES in September 2016, drinking water contributed 14% of the average lead exposure in children aged 13 to 36 months. 

A quality limit for drinking water of 10 µg of lead per litre has been set by the regulations. To comply with this quality limit and minimise oral exposure of the population to lead, several solutions have been considered, including replacing pipes made of lead, and treatments modifying the quality of drinking water in order to reduce lead dissolution in the distribution network. 

With regard to the treatments, the addition of phosphoric acid or orthophosphates can be considered for moderately and highly mineralised water presenting an equilibrium pH of less than 7.5, in order to form a protective layer on the inner walls of the pipes. Accordingly, between 2003 and 2013, ten plants producing drinking water in the Ile-de-France region implemented treatment with orthophosphates. 

ANSES received a formal request to determine whether this orthophosphate treatment should be maintained, in view of the possible consequences of stopping the treatment in terms of the quality of the water supply and the destabilisation of the microbial ecology in the systems. It was also asked for clarification on the monitoring conditions that may be required, in the event that maintaining this treatment is shown to be warranted.

Agency conclusions and recommendations

Various measures have been taken to reduce exposure to lead from water intended for human consumption (removing public connections made of lead, etc.). However, the available data cannot be used to obtain an accurate and comprehensive assessment of the results of these measures. 

Acquiring data on the presence of lead in tap water is thus a priority, considering the many uncertainties as to the proportion of housing in which tap water presents a lead concentration above the quality limit. The Agency therefore recommends improving knowledge of the public drinking-water supply and private systems inside older buildings, in order to better estimate the population's exposure to lead from the ingestion of drinking water.  

With regard to the treatment of water with orthophosphates, the experts consider that in general it does enable the concentration of lead in tap water to be reduced. The extent of this decrease varies, however, according to the sites, mainly because of the characteristics of the water supply, the nature of the network, etc. Thus, treatment does not guarantee compliance with the regulatory quality limit for lead in drinking water at all times and at all points of use.

The available data cannot be used to precisely assess the effects of orthophosphate treatment on the quality of the water supply, whether during or after its implementation. No negative effects were reported by the water distributors interviewed regarding the overall physico-chemical or microbiological quality of the water supply treated with orthophosphates. The negative effects on the environment appear to be limited in the areas concerned by the treatment. Lastly, the available data are insufficient for assessing the specific health impact of treatment with orthophosphates in terms of reducing blood lead levels.

The Agency therefore recommends accompanying any new implementation of orthophosphate treatment by studies to better determine the different impacts of the treatment, especially on the microbiological quality of the water supply and on the environment. A biomonitoring study, for example, could help assess the health impact of treating drinking water with orthophosphates.

Ultimately, the Agency considers that reducing population exposure to lead remains a priority public health objective and requires a combination of measures. Treating the water supply with orthophosphates is one possible collective protection measure, but is not in itself sufficient. In addition to this treatment, there are various other strategies to limit exposure of the population to lead through ingestion of water:

• treating drinking water at the production stage, by neutralisation, remineralisation or carbonate removal, with the treatment adapted to the initial quality of the water; 
• interventions on the distribution network: continued replacement of the connections in the public domain, replacement of indoor pipes (private systems) or renovation;
• improving the information provided to professionals and users, particularly those living in older housing.

Lastly, the Agency reminds consumers about some simple measures that can be implemented:

• let the tap run before using water for drinking or cooking food if it has been standing in the pipes for a long time. On the other hand, this water can be used for other non-food uses, in order to avoid waste;
• do not use water from the hot-water circuit for preparing hot drinks and food, as a high temperature promotes the dissolution of metals.