3 Protecting drinking water and bathing water from microbial pollution

3.1 Introduction

Protection of human health from microbiological risks is a key aim of EU water legislation. Both the Drinking Water Directive and the Bathing Water Directive set microbiological standards to protect humans from possible infections resulting from water-based human or animal faeces. Where water status is impaired due to microbial pollution this can be reported as a main impact for failing to achieve good status of surface waters and groundwater.

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3.2 Causes of microbiological pollution

Microbiological pollution caused by microorganisms such as bacteria, viruses and protozoa. Micro-organisms can cause severe health problems when ingested including gastrointestinal diseases, cholera, typhoid and hepatitis. Possible risks are generally well under control and infections are rarely lethal in Europe. Water-based infections of humans can either by drinking polluted water or through body contact e.g. bathing in contaminated water.

Microbial pollution of natural waters can be assessed using certain faecal indicators, which indicate the presence of human or animal faeces in wastewater. The threat to human health comes from ingestion of coliphage viruses that infect the bacterium Escherichia coli (EPA, 2015). Therefore, we can assess health risks by monitoring indicative bacterial concentrations.

Such micro-organisms are typically found in sewage water, or washouts from fields for livestock grazing, manure-spreading and other farming activities. In addition, wildlife and domestic animals as well as humans bathing or sporting in surface waters can a source of microbial pollution. Furthermore, some naturally-occurring microorganisms can be harmful to human health (WHO, 2003b).

The most frequent causes of microbiological pollution reported under the BWD is pollution from sewage water as a result of sewer system failures or activation of sewer overflows , water draining from farms and farmland, and animals and birds on or near beaches (EEA, 2016).

Studies on the influence of effluents from wastewater treatment plants and combined sewer overflows upon the microbial quality of surface water usually show an increase of faecal contamination following storms (WHO 2003b). The impact might be especially large in small river catchments, where the concentrations of microorganisms downstream from sewer overflows may be hundred times greater after a storm than in dry weather. However, the actual impact of CSOs also depends on numerous environmental factors, therefore an assessment needs to be site specific.

The principal problems, combined with the specific characteristics of each bathing area, lead to a complex combination of pressures and impacts. For example, heavy rain may cause flooding of nearby pastures resulting in wash-out of significant microbiological pollution into the bathing area. In Germany, authorities reported that two bathing areas on Lake Constance had to be closed for this reason in 2014, while in other areas such events occur much more frequently e.g. in the Walloon Region where  grazing of livestock on the meadows along the rivers was even prohibited to stop microbial pollution of the bathing sites. Other sources of microbiological pollution, e.g. public infrastructure, abandoned facilities or landfills near bathing water sites, may further complicate tracking the relevant source of pollution. An incidence at one bathing site in Portugal in 2013 was probably caused by a wastewater treatment plant not working properly (EEA 2015). But also bathers themselves when appearing in large numbers for extended periods can increase microbiological pollution of the water. In the Mediterranean this happens quite often throughout the bathing season (Saliba and Helmer 1990).

The BWD obliges the national authorities to monitor and report on bathing water quality. Regular monitoring and assessment has led to a better understanding of the causes of microbial water pollution. This has encouraged the development of targeted measures to reduce the microbial pollution in designated bathing sites. For example, Sweden has recently introduced a law that forbids all recreational ships and boats to discharge sewage into its territorial waters.

 

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3.3 Monitoring of microbiological pollution: role of the directives

The core principle is to identify faecal pollution sources and potential entry points into the aquatic environment, and to take action to reduce the presence of, or exposure to, hazards until they reach acceptable levels. Targeted measures can include emission reductions at municipal sewage discharge points, treatment works, combined sewer overflows and prosecution of illegal connections to combined sewers (WHO, 2003b).

The EU water industry directives prescribe monitoring of bacterial groups that are essential for assessing water quality for human use. Depending on the use of the water (bathing or drinking) different bacteria must be monitored.

 DWD:

  • Clostridium perfringens, including spores (if water originates from or is influenced by surface water)

  • Eschicheria coli

  • Pseudomonas aeruginosa (if water is offered for sale in bottles or containers)

  • coliform bacteria.

BWD:

  • Escherichia coli

  • intestinal enterococci

  • cyanobacteria.

The UWWTD does not require monitoring of specific bacteria, but instead prescribes monitoring of BOD, phosphorus and nitrogen. These indicate levels of nutrients that are able to support bacterial life (see also chapter 2 and Annex A3).

The European database on bathing water quality contains almost 1.1 million samples,  composing a time series of eight years (2008–2015). The data on bacterial concentrations covers bathing season which is generally from June to September.

Bathing sites are located in different categories of waters, each having their own geographical, physico-chemical and hydromorphological characteristics: coastal waters, lakes, rivers and transitional waters (typically estuaries and lagoons) (Table 3.1). Almost three-quarters of the designated bathing waters are on the coastlines of the sea; these are followed by lakes, which account for 22 % of all samples. The BWD defines quality classification limits depending on the surface water type. Therefore, unlike other water industry directives, the BWD provides data on microbiological pollution per water category but does not go as far as the WFD which stipulates the definition of surface water types within water categories.

Table 3‑1 BWD samples by water category

Type

BWD quality classification group

Number

Share of total (%)

Coastal

Coastal and transitional

944 530

74

Transitional

18 274

1.5

Lake

Inland

272 340

21

River

42 983

3.5

Total

1 278 127

100

On the other hand, the DWD provides data on the microbiological state of the water when it enters the distribution and supply system.  According to the UWWTD, Member States have to provide monitoring data on the water discharged directly from the wastewater treatment plant, which is still polluted with microorganisms despite its treatment in the plant (Wakelin et al., 2008).

 

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3.4 Microbiological pollution of bathing waters

According to the BWD, good bathing water quality is achieved if 95th percentile of all samples at the site in the most recent assessment period is lower than defined limits of intestinal enterococci and E.coli. Limits for coastal and transitional waters are 200 CFU/100ml of intestinal enterococci and 500 CFU/100ml for E.coli. For inland waters the limits are higher: 400 CFU/100ml for intestinal enterococci and 1 000 CFU/100ml for E.coli. For coastal and transitional waters, 2.2 % of all samples exceeded the limits, and likewise 2.2 % of all samples exceeded the limits for good bathing water quality in inland waters[1].



[1] Note that national authorities can report samples as having been taken in short-term pollution periods, and yearly assessments exclude them if replacement samples are provided. This review of sample statistics, however, uses all samples for its calculations. It includes those taken during short-term pollution events because these are typical examples of microbiological pollution.

Figure 3.1 shows bacterial concentrations in European bathing waters. The data since 2008 shows no clear trend in bacterial concentrations, although in the 2015 bathing season a decrease in bacterial concentrations especially for E. coli can be noted.

The shorter-term time series (paler trend lines) cover a larger number of European bathing water sites and generally shows higher average bacterial concentrations. This indicates that bathing waters added to the monitoring programme more recently are of lower quality.

Figure 3.1 All-European trends in intestinal enterococci and E. coli concentrations in bathing waters.                                                                                                                            

Figure 3.2 depicts bacterial concentrations per water category: coastal water, transitional water, lake and river. As expected, coastal bathing waters are of better quality than other water categories. They have fewer bacteria of both types owing to salt water providing harsher living conditions than freshwater. Coastal water bacterial concentrations are rather stable. E coli concentrations are around 49 CFU per 100 ml and intestinal enterococci concentrations around 27 CFU per 100 ml. The BWD classifies transitional waters according to the same standards. However, average bacterial concentrations are higher there than in coastal water, especially concentrations of E. coli (rising to 62 CFU per 100 ml in the 2015 season).

Bacterial concentrations in lake bathing waters were at their lowest in the 2013 season and rose again in 2014. E. coli reached 57 CFU per 100 ml and intestinal enterococci reached 30 CFU per 100 ml in the 2015 season.

Riverine bathing waters are the most polluted. They have exceptionally high concentrations of both E. coli (159 CFU per 100 ml) and intestinal enterococci (58 CFU per 100 ml) compared with other water categories, but with averages changing over the years.

Figure 3.2 Overall European trend in E. coli (left) and intestinal enterococci (right) concentrations by water categories (for bathing waters).

                  


 

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