Preventing the health risks associated with chemicals in drinking water

What is classified as drinking water and where does it come from?

Drinking water (DW) includes tap water and packaged water, mostly bottled, with the exception of natural mineral water. It is mainly produced from "raw" ground and/or surface water, which is treated to make it drinkable. DW is subject to specific regulations.

What are the sources of chemical contamination of drinking water?

Depending on where it comes from, this water may contain mineral elements of natural origin (fluorine, magnesium, calcium, etc.), some of which – such as arsenic – are known to be toxic to humans. Water resources can also be polluted by urban, industrial or agricultural human activities, or by accidental contamination.

How are chemicals in drinking water regulated?

In order to protect consumer health, the presence of chemicals is governed by European regulations, which have been translated into French law in the Public Health Code. Based on the work of the World Health Organisation, these regulations lay down maximum concentrations for around 40 chemicals or chemical classes in the water distributed to consumers, in particular through the amended Ministerial Order of 11 January 2007. These maximum concentrations are of two kinds:

• "quality limits", which are set to protect consumer health;
• "quality references", which are set to verify the proper functioning of water treatment plants or to avoid any alteration of the organoleptic properties of the water supply, i.e. its colour, odour or taste and, ultimately, to protect consumer health.

The Regional Health Agencies (ARSs) conduct regular checks of DW quality and compliance with quality requirements.

Can the regulatory maximum concentrations of chemicals in DW be exceeded?

The management of situations of non-compliance with the quality requirements for water supplied to the consumer's tap is strictly governed by regulations, which allow for the possibility of exceeding the quality limits in exceptional cases, provided that:

• this exceedance is temporary and does not pose any risk to health;
• it is not possible to implement immediate corrective measures such as treatment, a switch to a different resource, or the use of interconnections, for example, to maintain a water supply that complies with the quality limits;
• measures are taken by local health authorities to restore the compliance of the water supply within the prescribed period of time;
• an exceptional maximum value (guideline value) is set and applied to ensure that public health is not put at risk during this period.

How are these situations managed? 

To support the health authorities in managing these situations in DW, the Directorate General for Health asked ANSES to assess the health risks, from a series of chemicals, associated with the consumption of water in which the concentrations exceeded the quality limits or references. For 16 substances, therefore, the Agency determined maximum allowable concentrations for drinking water consumption, on the basis of health considerations, for the entire duration of the exemption. These are known as "guideline values". This work was published in a 2007 report (PDF). Since then, the expert appraisal work has continued and new opinions have been published for the following substances: bromates (PDF), chromium (PDF), boron (PDF) and manganese (PDF). In addition, to take account of advances in scientific knowledge, certain parameters (such as selenium (PDF) and vinyl chloride (PDF)), which had been addressed in opinions published in the above-mentioned report, were updated.

In some cases, due to a lack of data, no guideline value can be determined.

On the basis of the Agency's opinions, therefore, the public authorities can take appropriate management measures such as improving the quality of water from the resource, introducing DW treatments, mixing water by interconnecting networks, restricting tap water consumption, etc., in order to best manage specific situations where the regulatory limits are exceeded and ensure that compliance is restored.

What about non-regulated chemicals present in DW?

As well as monitoring the 40 regulated substances, the services responsible for DW quality are watchful for the possible presence of other substances in this water. This work includes organising forecasting campaigns in DW. In addition, at the national level, ANSES's Nancy Laboratory for Hydrology regularly conducts exploratory studies on the detection of some of these substances (such as haloacetic acids, chlorates and phthalates (PDF) or perfluorinated alkyl compounds (PDF)) in the water used to produce DW and in treated water.

For several years now, the Agency has been regularly consulted about the health risks associated with the detection in DW of substances for which no regulatory quality limit or reference has been set, such as drug residues (PDF) or perchlorate (PDF). In these cases, ANSES's opinions seek to provide a guideline value in drinking water for the chemical in question. This value then enables the public authorities to determine the concentration from which measures should be taken: informing the public, restricting consumption, remedial actions, etc.

These health risk assessments for non-regulated substances may concern specific local situations such as natural contamination with thallium, industrial contamination with n-nitrosomorpholine (PDF) or morpholine (PDF), or accidental contamination with nitroglycerin (PDF) released following a warehouse fire.

How are guideline values for chemicals in drinking water developed?

Regardless of whether the expert appraisals concern regulated or non-regulated chemicals, development of a guideline value is always based on two main steps:

• characterisation of the hazard to human health of the chemical, leading to determination of a toxicity reference value;
• characterisation of the population's exposure to the chemical from drinking water, based on the concentrations measured in DW and taking into account other sources of human exposure, in particular food. 

ANSES's opinions also document the capacity to analyse the substance in drinking water and the options for treatment to reduce its concentration in the water. In practice, health risk assessments of a chemical in DW are usually conducted by comparing the concentrations measured in drinking water with the guideline value determined for that chemical.

This method of developing guideline values for chemicals in DW is described in the 2007 report. This methodological guide is being updated following an internal request at the Agency.