Due to climate change, the quality of surface water in the future may deteriorate to such an extent by 2050 that it will be unsuitable for drinking water production unless extra measures are taken. This situation occurs during dry years when water quality standards are exceeded during periods that last from days to months. These exceedances are already taking place during very dry years and may increase in the future. The extent of this increase will depend on the degree of climate change.
Surface water as drinking water source under pressure
That surface water as a source of drinking water is under pressure can be concluded from exploratory calculations made by Deltares. The National Institute for Public Health and the Environment (RIVM) analyzed the calculations for the Delta Programme on Freshwater. The results apply to almost all locations in the Netherlands where surface water is abstracted for drinking water production (abstraction points). This surface water is used for the drinking water supply of about 40% of the Dutch population.
The water quality deteriorates during periods of low river discharge. This is because the effect of spills from sewage water treatment plants is much larger due to less dilution.
Measures for individual abstraction points recommended
Nearly half of the abstraction points are located in branches of canals and rivers with very low water discharge during dry periods. In these water sections - known as stagnant zones - the water level is maintained artificially at a fixed level. Here a small variation in discharge may seriously affect the calculated concentrations of substances. It is therefore recommended that each abstraction point is individually analyzed with all parties concerned: water authority, national authority, province and drinking water company. The risks can then be weighed up and effective measures developed. Such measures are, for example, tightening up the authorization of substances, the reduction of spills, the flushing of stagnant zones and the extension of the drinking water treatment process.