Member States shall take all measures necessary to ensure that regular monitoring of the quality of drinking water is implemented to check that the water available to consumers meets the Directive requirements, and particularly the parametric values settled. Samples of drinking water shall be taken so that they are representative of its quality throughout the year.
Appropriate monitoring programmes shall be established for all drinking water. Those monitoring programmes shall be supply-specific, taking into account the outcomes of the risk assessment of the catchment areas for abstraction points and of the supply systems.
The following elements shall be monitored:
(a) the parameters listed in relevant parts of Drinking Water Directive;
(b) the parameters listed for the purposes of the risk assessment of domestic distribution systems;
(c) the substances and compounds included in the watch list;
(d) the identification of hazards and hazardous events; and
(e) operational monitoring.
The Drinking Water Directive sets that:
- sampling points shall be determined by the local competent authorities according to the rules specified;
- Member States shall implement processes and procedures to comply with the specifications for the analysis of parameters;
- Member States shall ensure that additional monitoring is carried out on a case-by-case basis of substances and microorganisms for which no parametric value has been set in accordance with DWD, if there is reason to suspect that they may be present in numbers or concentrations which constitute a potential danger to human health.
Moreover, the Drinking Water Directive provides also requirements to Member States for set down rules dedicated to remedial actions and restriction of use in case of any failure into meet the parametric values.
Regardless of whether any failure to comply with the parametric values has occurred, Member States shall ensure that any supply of water intended for human consumption which constitutes a potential danger to human health is prohibited or the use of such water restricted and that any other remedial action that is necessary to protect human health is taken.
Where the non-compliance with the parametric values is considered to be a potential danger to human health, Member States shall as soon as possible take all of the following measures:
- notify all affected consumers of the potential danger to human health including prohibition or restriction of use or other action;
- give, and regularly update, the necessary advice to consumers on conditions of consumption and use of the water; and
- inform consumers once it has been established that there is no longer a potential danger to human health.
The DWD sets also possibly derogation to the parameters. In duly justified circumstances, Member States may provide for derogations provided that such derogations do not constitute a potential danger to human health. Such derogations are limited to as short a period as possible and shall not exceed three years in duration.
In exceptional circumstances, a Member State may grant a second derogation, it shall communicate the results of the review, along with the grounds for its decision on the second derogation, to the Commission. Such a second derogation shall not exceed three years in duration.