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A2.1      Introduction

Legislation

The DWD aims to ensure that water intended for human consumption is safe. It must be free of any microorganisms, parasites or substances that could potentially endanger human health. The directive applies to all water intended for human consumption apart from natural mineral waters and waters that are medicinal products.

The directive came into force in 1998 and replaced Directive 80/778/EEC. 27 Member States of the EU have enacted it in their national legislation and have to comply with its requirements (Croatia do not yet have to comply with the DWD).

The directive:

• sets quality standards for drinking water at the tap (microbiological, chemical and organoleptic parameters) and the general obligation that drinking water must be wholesome and clean;

• obliges Member States to monitor drinking water quality regularly, to take remedial action if the monitoring reveals problems and to provide consumers with adequate and up-to-date information on the quality of their drinking water;

• allows Member States to exempt water supplies serving fewer than 50 persons or providing less than 10 m³ of drinking water per day on average, drinking water from tankers, drinking water in bottles or containers and water used in the food-processing industry, where the quality of water cannot affect the wholesomeness of the foodstuff in its finished form.

Drinking water quality parameters

The directive sets standards for the most common organisms and substances that can be found in drinking water. A total of 48 parameters must be monitored and tested regularly. In general, the basis for the standards is the WHO’s guidelines for drinking water and the opinion of the EC’s Scientific Advisory Committee.

Annex I of the directive divides the parameters into microbiological parameters, chemical parameters, indicator parameters and radioactivity.

The two microbiological parameters are E. coli and enterococci. Their parametric value is a substitute for zero. In other words, these organisms should be absent from drinking water to guarantee its quality.

The indicator parameters are not directly relevant to the quality of water. They indicate that something has changed in the source, the treatment or the distribution of the water. This needs to be investigated and may require urgent action. Most indicator parameters do not pose a direct threat to human health, but they might have an indirect impact through the appearance, taste or odour of the water, making it less acceptable to the consumer, or they might interfere with proper treatment. For example, organic matter may make disinfection inadequate.

 The chemical parameters were selected for their potential impact on human health, and they do not closely match the list of priority substances under the WFD. Apart from accidents, chemicals are almost never present in drinking water in concentrations that cause acute health effects. They include trace elements, such as arsenic, nickel or lead, and other substances, such as cyanide, polycyclic aromatic hydrocarbons or nitrogen compounds (nitrate and nitrite). In particular, these parameters cause ‘blue baby syndrome’ (see Chapter 5). Furthermore, the impact of these chemicals depends on how they affect the human body. Mostly, the parametric values are based on lifelong exposure and an average intake of 2 l of drinking water per person per day. There is a distinction between threshold and non-threshold substances:

• Threshold chemicals have no impact on human health when concentrations are below the threshold. In cases of non-compliance, the impact depends on the amount of exceedance, the duration of exposure and the safety factor that has been used in setting the parametric value. This differs for each parameter, based not only on health impacts but also on technological capability and ability to analyse substances in the water.
• Non-threshold chemicals, such as pesticides, have no threshold below which there is no potential effect on human health. Dealing with them uses a risk approach that mostly accepts one additional death through drinking water among 1 million people; this is stricter than the value that the WHO currently uses (1 in 100 000 people). If we know the level of non-compliance and the duration, we can then try to estimate the potential impact on human health in a particular Member State or water supply zone (Hulsmann et al., 2015).

Member States may, for a limited time, deviate from the chemical quality standards specified in Annex I of the directive. This process is called ‘derogation’. A derogation can be granted if it does not constitute a potential danger to human health and if there is no other reasonable means of maintaining the supply of water intended for human consumption in the area concerned.

Drinking water quality must be checked at typical locations. They must represent the water source, treatment plant, storage facilities, distribution network, points at which water is delivered to the consumer and points of use. Therefore, where to sample the water depends on the parameter and the potential risk. For instance, excess lead mostly comes from domestic pipe systems and is not a problem in waterworks, so it is all the more important to sample water for lead at the tap, after it has gone through the distribution network.

Water supply zones and dependency on environmental pressures

Assessing drinking water quality is based on the spatial scale of a water supply zone. A water supply zone is ‘a geographically defined area within which water intended for human consumption comes from one or more sources and within which water quality may be considered as being approximately uniform’ (Annex II, DWD). This means that a water supply zone could be a waterworks that collects and processes raw water from two drinking water reservoirs; or it could also be an elevated tank that supplies a district with drinking water.

 The directive makes a distinction between large and small water supply zones. Large water supply zones supply more than 1 000 m³ of drinking water per day, on average, or serve more than 5 000 persons. Small water supply zones are subdivided into three further categories: category 1 supplies 10–100 m³ per day; category 2 supplies 100–400 m³ per day; and category 3 supplies 400–1 000 m³ per day.

The level of treatment required in a particular water supply zone depends on the quality of water it receives from its sources. Water efficiency measures are worth exploring if there are shortages of raw water or if polluted sources require costly treatment. The option to transfer water from another basin with abundant resources would need to be assessed with the financial and environmental costs of transfer against the costs of treatment and possibility to reduce pollution at source (for costs of transport see also e.g. Kraemer et al., 2007; Holländer et al., 2008). Measures to reduce demand and clean up pollution should be exploited before considering the need to transfer water between basins. The DWD itself does not request any information about the quality of raw water, its source (in terms of transfers from other water bodies) or the intensity of treatment necessary (see also Chapter 3). Integrated approaches to evaluate the most appropriate solution taking source water quality into account  be implemented in an integrated way under the WFD.

Information to the public

Large and small supply zones have the same minimum water quality requirements. However, monitoring requirements differ. Reporting to the EC is mandatory for large water supply zones. Member States are also obliged to report the water quality of small water supply zones if data are available.

Every three years, Member States must digitally report drinking water quality to the EC. They are also obliged to publish a national report to the public. Table A2.1 lists links to the national drinking water quality reports or information about the reporting period 2011–2013. Furthermore, national country reports show drinking water quality in the reporting period 2011–2013 in a nutshell (map viewer on dwd.etcicm.cenia.cz). All reported data are available in the WISE databases.

Table A2.1 Links to national drinking water reports and information for 2011–2013