Climate-proof drinking water, now and in the future

Drinking water in the Netherlands is treated to high quality standards and then delivered to customers through the underground distribution system. The distribution system consists of trunk mains, distribution mains and connection pipes. The trunk mains are the largest and transport the water from the treatment and storage location to residential areas and companies. The distribution mains then divide the water among the residents. The connection pipes convey the drinking water to individual homes and companies where it is used. To illustrate, the average person in the Netherlands consumes about 120 litres per day at home.

Drinking water and temperature: not too cold, not too warm, but just right

Before the water enters the distribution network it is controlled for its quality; and when it leaves the distribution network it must also meet high quality requirements. One of these is that it must not be warmer than 25˚C at the tap point; and water utilities control this aspect by regularly collecting water samples.

The water utilities have only a very limited amount of control over the water temperature. The temperature of the water entering the network is a function of the temperature at the source, which can be groundwater or surface water; in the case of surface water the temperature varies seasonally. Between the treatment site and the tap point the water’s temperature is affected by the temperature of the ground around the pipes. This is especially the case for distribution mains and connection pipes, which involve small pipes in which the water does not flow rapidly with regularity. The water temperature therefore quickly increases to the temperature of the surrounding ground, which is not constant through the course of the year. The outside temperature affects the temperature of the ground. For example, when it freezes for a long period, the upper layer of the ground also freezes. While in the summer, during long hot periods, the ground will slowly warm up: the shallower the layer, the warmer the ground becomes. The ground takes more time to react to temperature changes than does the air. The depth at which the pipes are today installed (about 1 meter) has, up until now, been sufficient to assure an adequate drinking water temperature.

Threats from climate change

According to the climate scenarios of the KNMI (Royal Netherlands Meteorological Institute), around 2030 the average summer temperature will be 1˚C warmer than under the current climate (1981to 2010, inclusive). Around 2050, the average summer temperature will be between 1 and 2.3 ˚C warmer than today; while around 2085 it will even be between 1.2 and 3.7 ˚C warmer. For purposes of comparison, the summer of 2018 was 1.9 ˚C above normal. As the summers become warmer, so too will the ground. KWR studies have shown that hotspots – i.e., locations that are warmer than average – can be identified in the water distribution system. For instance, locations that are always exposed directly to the sun, or are under asphalt, or are in the vicinity of heat sources, such as heat networks. In these hotspots there is a risk that the drinking water temperature will occasionally rise above 25˚C. This occurs under the current climate on an incidental basis, at the most; but around 2050 and thereafter it could happen for several weeks every year. Potential additional hotspots will also arise due to developments related to the energy transition. The subsurface is becoming increasingly full of electrical cables, heat networks, ATES installations, all of which increase the chance that the temperature of drinking water in any pipes sufficiently close by will be affected. This is not desirable and preventive measures are called for.

Solutions are available

Water mains last for many decades. To avoid problems, it is therefore important to start implementing solutions as soon as possible. With regard to excessively warm drinking water, the solution is to prevent new hotspots. KWR has studied the effectiveness of different measures to this end. A sufficient distance from the heat source is important; KWR and Deltares are currently researching the minimum distance required. Shading by buildings and by vegetation is effective – the latter particularly so, because it removes heat from the air through evaporation and keeps the soil moist. The deeper installation of pipes is an option, though an expensive one. Other measures only have a local impact, for instance, insulating or cooling the drinking water.

The measures involve tailored work and the water utilities cannot achieve the task alone, particularly since many of the measures mentioned actually fall under the responsibility of other stakeholders active in the surface and subsurface space. To address flooding and heat stress, many municipalities are now thinking about greening their neighbourhoods. If we incorporate the objective of sustainable and wholesome drinking water immediately in the planning, then we create win-win situations. It would therefore be good to include drinking water temperature as part of the municipalities’ sustainability visions.

KWR has studied the effectiveness of different measures to this end. A sufficient distance from the heat source is important.