Increased average temperatures, greater volumes of precipitation, altered drainage patterns, evaporation and groundwater formation are creating new challenges for the supply of drinking water. Extreme weather events such as heatwaves, droughts, torrential rain, storms, high rivers and floods can, as with sea level rises, lead to quantitative and qualitative changes to the water in the raw water resources on which the supply of drinking water depends.
Other effects that may arise in some places are a lack of water and salt water ingress in water sources used for drinking water.
Aside from the direct physical strain on the drinking water supply infrastructure, the scope of chemically and microbiologically dependent health risks may increase.
Pollutants and natural organic material are already being transported from drainage basins out into lakes, watercourses and associated water sources.
Climate change is creating the conditions for increased transport as a result of increased total precipitation and higher rivers, milder winters and more precipitation in wintertime in the form of rain and/or frequent snow melts, in addition to a longer growing season. This may result in changes to the chemical and microbiological quality of the raw water, increasing the risk of disruptions to water treatment plants and the risk of an impact on the quality of their output.
The availability and quality of groundwater might also be affected. Increased water availability and higher flow rates has an impact on conditions in the soil and the opportunities for treatment in the unsaturated zone. This can affect the quality of the groundwater and place great demands on water treatment plants in terms of purification.
Risks for surface water
About half of the total supply of public drinking water is dependent on surface water. A further quarter uses what is known as artificial groundwater, where the surface water is infiltrated down into groundwater resources to reinforce the groundwater. The remaining quarter is based entirely on groundwater, without artificial infiltration.
Surface water resources are more and more rapidly exposed than groundwater resources to a range of risk factors. They are therefore particularly vulnerable to changes in land use and sources of pollution within their drainage basin. Climate variables such as air and water temperatures have a significance, as do the intensity and variation of precipitation and flow rates. Torrential rain linked to flooding increases the risk of chemical and microbiological pollutants entering water sources. The flow rate in watercourses can also be affected, with a greater risk of erosion and landslides in some parts of the country.
The effects of climate change can in themselves result in water treatment plants' traditional microbiological and chemical barriers loosing their effectiveness. The purification processes are rarely adapted to dealing with higher levels of pollutants. Continued increased humus levels in raw water, primarily in the southern and central parts of the country is expected to also lead to the barrier effect of, for example, chlorine disinfection decreasing. In particular, surface water treatment plants can at present be considered as sensitive to the effects of ongoing climate change. Climate change also entails increased risks for groundwater treatment plants, which have more limited protective barriers.
Even with the current climate, there are sometimes low water flow rates and water shortages in parts of the country. In the future, it is expected that low flow rates will occur more often in southern Sweden, primarily in eastern Götaland. This may lead to drinking water shortages.