The risks of bacterial contamination and chemical pollution associated with water sources have been significantly reduced in France today, thanks to the implementation of a series of protective measures between the water source and the consumer’s tap:

• protection zones around water intake points used for drinking water production,

• appropriate treatment processes,

• disinfection processes,

• design and maintenance of distribution networks.

Understanding the risks associated with water resources

While cities have the means to monitor water quality and implement treatments adaptable to potential quality degradation, this is not always the case for small municipalities, which primarily rely on groundwater—generally of higher quality than surface water—but cannot afford the cost of sophisticated treatments in the event of resource contamination.

Mountain water, often poorly filtered by shallow soil and a fractured subsoil, treated little or not at all, and sometimes distributed through dilapidated networks, poses a high microbial risk compared to water distributed in cities. Furthermore, this risk can be significantly increased during heavy rainfall. Runoff events cause a deterioration in the quality of surface water and poorly protected groundwater.

Finally, private wells pose a high risk of contamination: volcanic areas prone to arsenic contamination, and shallow aquifers highly vulnerable to microbiological or chemical pollution. Monitoring their quality is the responsibility of the owner, and neither their quality nor their uses (drinking, irrigation) are well understood.

Treating raw water before distribution

Apart from well-protected deep sources, the quality of raw water must be treated before it is supplied for human consumption in order to comply with the provisions of the Public Health Code. Broadly speaking, there are two types of treatment:

• clarification by settling or filtration,

• disinfection, most often using ozone or chlorine.

Treatment failures or malfunctions pose a risk of an epidemic if the raw water is contaminated. The development of monitoring probes (for turbidity in raw and treated water, and chlorine in treated water) and remote alarms is a key safety factor.

Distribution conditions also affect the quality of the distributed water. The most feared accident is “backflow of wastewater” into the system, which results from the combination of an unprotected connection feeding a wastewater treatment plant and a drop in pressure in the drinking water system.

Monitoring water-related risks and assessing health risks

Several approaches have emerged over time for controlling waterborne risks.

Until World War I, cholera and typhoid epidemics raged throughout Europe, claiming thousands of lives each year. The work of Snow in Great Britain and Pasteur, in particular, helped raise awareness of water’s role in the spread of these epidemics. This is why, starting in the late 19th century, drinking water networks were built in major cities such as Paris and Lyon to bring water to residents’ homes, while the construction of sewer systems addressed the need to remove wastewater. Water quality control was established in France at the beginning of the 20th century.

Today, in France, the management of health risks related to water pollution and the enforcement of regulations fall under the jurisdiction of the Ministry of Health and the Regional Health Agencies (ARS). The French Agency for Food, Environmental and Occupational Health & Safety (ANSES) is responsible for risk assessment and management support, while Santé publique France is responsible for epidemiological surveillance and public health alerts.

About sixty compounds are currently subject to regulation. However, despite advances in analytical techniques, it is impossible to routinely analyze all toxins and pathogenic microorganisms; analysis times are sometimes incompatible with the immediate management of water contamination.

The quantitative risk assessment approach, which emerged in the 1980s, allows for the evaluation of risks attributable to agents for which the dose-response relationship and concentrations in distributed water are known. In fact, this approach can only be applied to a small number of agents and situations.