Drought and Public water supply in the EU

10.10.2024
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Drought and Public water supply in the EU

3.1 Key facts

The public water supply system in the European Union is responsible for providing about 474 million citizens with an average of 156 litres per day of high-quality water for consumption (European Commission 2016).

The system consists of around 11,000 large and 85,000 small supplies, which serve 80% and 20% of the population respectively. The freshwater abstracted for this system comes in roughly equal amounts from groundwater and surface water sources. The drinking water is then provided to households by publicly owned enterprises in more than 60% of the EU water infrastructure (Council of the European Union 2016), whereas the remainder is provided by regulated entities with different levels of private ownership. Safe drinking water is not only essential for public health, but also economically important, as it is a precondition for the development of economic activities. Therefore, decreased quantities of adequate quality water can have high social and economic costs for the EU.

Drought events can reduce groundwater and surface water levels, which are the main sources of drinking water in the EU. This decrease affects water availability, and, at times, the level of water quality required of fresh water for public water supply. The recent 2022 drought event affected the water supply capacity of various municipal areas in Europe. For example, more than 100 of these in France had water supply issues and drinking water had to be delivered by truck (Toreti et al. 2022) while water use was restricted in nearly all metropolitan departments of France. In Italy too, local authorities restricted water use during the summer of 2022

Risk (public water supply)

Drought events can affect the availability of water for household supply, both in terms of water quantity and quality, as previous droughts in Europe have shown (Van Lanen et al. 2016; Ahopelto et al. 2019; Bangash et al. 2013). For this reason, the risk for the public water supply system is defined here as the risk of household consumption water demand not being met due to drought. This encompasses both the possibilities that water availability is too low, either because of water quantity or quality, and that demand is too high, ultimately leading to unmet demand.

Exposed elements

The risk of unmet water demand poses a threat to the household water consumer, whose water is generally supplied by water supply companies and has to comply with the European Drinking Water Directive (European Commission 2014).

Climate signals & Hazards

The risk that household water demand is not met emerges during droughts due to the combination of insufficient precipitation and high temperatures.

Insufficient precipitation results in reduced groundwater and lower surface water levels in the streams and reservoirs that are used as sources for drinking water production, with accumulated water deficiency from previous drought events acting as a stressor in this situation (Van Lanen et al. 2016). At the same time, high temperatures further reduce recharge potential by causing increased evaporation. Moreover, they can also be responsible for the decreased pump cooling capacity of the pumps used to extract water, and this may cause decreased water abstraction capacity.

These climate signals and hazards can also negatively affect water quality. Water in lower volumes often has an increased concentration of toxic substances.

In addition, increased water temperature due to high air temperatures is connected to the development of algal blooms and growth of bacteria. Reduced water levels can also contribute to saltwater intrusion, which leads to increased water salinity and resulting quality deterioration (Van Lanen et al. 2016; Mullin 2020).

All these processes decrease water availability for provision, as a certain degree of quality is required for household consumption.

Vulnerability drivers & Intermediate impacts

Many societal drivers can aggravate the situation for the public water supply system. For instance, increased soil sealing, driven by high urbanization rates, hinders groundwater recharge. In addition, higher demands by other sectors, such as agriculture or industry, contribute to reduced water availability for drinking purposes (Flörke et al. 2018).

The public supply system suffers further losses during distribution due to outdated pipe networks (Ahopelto et al. 2019), which cause water leakages. Pipes can also suffer stress from dried-out soils, which can contribute to pipe bursts. However, this may be countered by the lower pressure from water inside the pipes. The problem of reduced water availability during droughts is exacerbated by a lack of diversity in supply sources (Mullin 2020), which ultimately requires more efficient water use and allocation (Mereu et al. 2016). The quality of the water available for public supply is also a concern during droughts, as the concentration of contaminants may increase as less water is available to dilute them. Sources of contamination can be societal such as wastewater pollution (WHO Regional Office for Europe 2022).

In some cases, insufficient water treatment capacity can prevent this water from getting treated back to a level that is appropriate for consumption. This can generate increases in costs, as purification and monitoring procedures become more frequent and expensive. However, in specific cases, it may also pose a threat to human health if there is insufficient quality monitoring capacity to prevent this water from being provided to households (European Commission 2014), especially in the case of small or unofficial supplies, where insufficient monitoring may also stem from a lack of legislation (European Commission 2014; Gunnarsdottir et al. 2017).

Finally, dynamic aspects that lead to high water demand also contribute to this risk. For instance, high urbanization rates can increase local risk (McDonald et al. 2014; Mereu et al. 2016). In addition, tourism seasonality can increase demand concentration in certain places and for certain periods of time (Martínez-Ibarra 2015; Mereu et al. 2016). Especially those places that show an economic dependency on tourism may be reluctant to introduce restrictions (Mereu et al. 2016), which may drive water planners to pursue the expansion of reservoir storage space, rather than take measures to control high demand. The expansion of reservoir storage contributes to an over-reliance on reservoirs: this policy can heighten the system’s vulnerability to water shortages, as it undermines the incentive to pursue other adaptation actions against droughts (Di Baldassarre et al. 2018).

3.3.3 Drought risk under current climate conditions

When looking into the drought risk for public water supply (Figure 31), we see demand for additional average annual water abstraction of up to 10%. These additional abstractions can pose challenges to suppliers in terms of treating and supplying water.

The highest extra abstractions in the most water-rich countries (Scandinavia) which have enough water to face such extra abstractions relatively easily. We can also observe slightly elevated values (up to 5% extra abstractions) in dry southern regions. Here regular demand is probably much closer to the maximum supply of freshwater resources (highest level of abstraction in southern Spain, Figure 30), meaning there is less room to accommodate extra abstractions.

Here it is likely that no further extra abstraction can take place during severe drought events and restrictions may come into force.

3.3.4 Drought risk under projected climate conditions

Figure 33:

Variation of drought risk for water supply between current and projected climate conditions. Risk is measured as average annual increase in drought-induced abstraction compared to the average expected value under current climate conditions. Results of future simulations forced with 11 climate models in RCP 4.5 and RCP 8.5 are averaged for each warming level (+1.5 °C, +2.0 °C, +3.0 °C). The analysis was conducted at NUTS-2 level, for those territorial units with sufficient data for computation.

Figure 34:

EU-aggregated PML curves for public water supply under current and projected conditions for +1.5 °C, +2.0 °C, +3.0 °C warming level scenarios. The solid black line is the PML curve for the historical period, while the dotted black line traces out the median of future simulations forced with 11 climate models in both RCP 4.5 and RCP 8.5.

The shades of yellow denote the climatic variability of future simulations: dark yellow is the interquartile, while pale yellow represents the lower and upper quarters.

In relative terms, risk is projected to increase (Figure 33) in almost all Europe and especially around the Mediterranean, where large increases in drought-induced water abstractions can be expected. Considering the level of exposure, Spain would be the most affected country with great relative increase in abstraction especially in warming level +2 °C and +3 °C. This may lead to increased competition on water resources, additional stress to water providers and potential restrictions on domestic water use or even taps running dry if demand cannot be met. The latter is likely in

the Mediterranean region, since in that area there is also currently a link (not shown here) between drought events and reductions in water abstractions, illustrating that even usual demand cannot be met during current extremes. However, given the few precedents of taps running dry in other regions, the model could not project drought-induced reductions in water abstractions under projected climate change conditions on a European scale (due to model uncertainty). The PML curves (Figure 34) show a slight rise in risk of increased abstractions with higher warming levels at European scale. Whether this would result in actual increases depends on whether policies on water restrictions and allocation priorities change.

Source :

Rossi, L., Wens, M., De Moel, H., Cotti, D., Sabino Siemons, A.-S., Toreti, A., Maetens,W., Masante, D., Van Loon, A., Hagenlocher, M., Rudari, R., Meroni, M., Isabellon, M., Avanzi, F., Naumann, G., Barbosa P. - European Drought Risk Atlas, Publications Office of the European Union, Luxembourg, 2023, doi:10.2760/608737, JRC135215