2023

Interview with Michelle van Vliet: "Owing to drought, there is less water available to dilute contaminants."

What are the effects of droughts and heat waves on the water quality of rivers worldwide, including the Meuse? Michelle van Vliet, Professor of Water Quality and Sustainable Water Systems at Utrecht University, is researching this. She talks about the results and what she thinks needs to be done.

Globally, 30% of the population is suffering from  water shortage. This percentage is as much as 40% of the world's population if we take into account water quality, in addition to the amount of water needed by different sectors. This is according to research by Michelle van Vliet from the Department of Physical Geography at the Faculty of Geosciences, Utrecht University.

She and her colleagues developed a water scarcity concept in which water quality is included in the calculations. "Many studies on water scarcity only look at the amount of water: how much water do we need and how much is available?" she explains. "We also included quality and the quality requirements by sector."

Quality requirements by sector

In many parts of the world, including the Netherlands, the quality of water in rivers is not good. "Climate change only aggravates this," says Van Vliet. Her research focuses on the effects that global changes have on the availability and demand for good-quality water. In addition to climate change, the growing world population plays an important role. The demand for clean water is increasing, but at the same time more pollutants are entering our water, especially in areas with little waste-water treatment. 

Apart from households, much water is used in agriculture, mainly for irrigating crops and additionally for livestock farming. Furthermore, companies and industries use large amounts of water, as does the power sector for cooling power plants. The researchers also looked at the quality requirements of different sectors and when water scarcity exists for each sector. For example, for irrigating crops in agriculture, there cannot be too much salt in the water and, for the energy sector, the water temperature cannot be too high.

Increase in chemicals

The study found that large parts of the world suffer from poor water quality. However, the type of water quality problems varies globally, Van Vliet observed. For instance, developing countries are especially struggling with organic pollutants and pathogens in water, often caused by poor sanitation and leaky sewers. Due to limited capabilities to purify water, such concentrations are too high in large parts of Asia, Africa and South America. 

In affluent countries, the main issue is the huge rise of man-made substances, she says, such as pesticides, medicine residues and PFAS (per- and polyfluoroalkyl substances). "These are often difficult to remove or it is expensive to purify the water. There is a lot of focus on this and rightly so."

Less dilution

The study further revealed that water demand increases especially when there is both a drought and a heat wave. "Both are expected to become more frequent and extreme globally due to climate change," says Van Vliet. "This means that less water flows through rivers, including the Meuse, in summer, while the demand for water is likely higher: this means there is an imbalance between the availability of good-quality water relative to the demand."

Photo 11: Michelle van Vliet, Professor of Water Quality and Sustainable Water Systems at Utrecht University.

At the same time, water quality is often worse during these periods of drought, she says, as there is less water to dilute contaminants. "Salinity and concentrations of pollutants that are difficult to degrade then increase. As a result, water quality standards are increasingly being breached." This is mainly due to discharges from industry and from waste-water treatment plants. 

Concentrations of medicines in rivers, including the Meuse, become higher in many cases during dry periods. Van Vliet cites as an example the drug carbamazepine, which is used as an anti-epileptic and in bipolar disorders, and has been found in the Meuse, among other rivers. During the 2018 drought, this caused the target values of the European River Memorandum (ERM) to be exceeded. Drinking water companies from the river basins of Meuse, Rhine, Danube, Elbe, Ruhr and Scheldt can sustainably prepare drinking water using natural treatment methods if surface water meets these ERM target values.

The impact on the Meuse

In addition to their global research, Van Vliet and her colleagues conducted two studies on what the droughts and the heat waves mean for the water quality of the Meuse River specifically. The research also clearly showed that when the flow rate  is low, there is less water to dilute contaminants. “The concentrations of pollutants then go up, as do salinity levels. The water temperature rises, which increases the amount of algae."

Remarkably, drought and high temperatures do not mean deterioration of water quality for all substances, she continues. "Thus, when rainfall is low, less fertiliser and pesticide residue flows from farmland into ditches and rivers. Some contaminants also break down faster at high temperatures."

Adapting to changes

The researchers looked at how best to deal with such changes to prevent further deterioration of water quality. Van Vliet: "Especially for rain-fed rivers like the Meuse, it is important that we start taking into account lower river flow rates and more frequent droughts when issuing discharge permits. We need to avoid higher concentrations of hazardous substances in rivers during those warmer, drier summers. In short, greatly reduce the amount of discharged substances, taking into account the amount of water in the river."

Van Vliet mentions the fact that some of the Dutch discharge permits are quite outdated and assume there is much more water in the rivers than now and in the future. "Updates are needed and, when doing so, it remains important to properly co-ordinate discharge permits with our neighbouring countries."

In addition to better permits Van Vliet stressed that, in view of more frequent droughts, we need to better retain water instead of conveying it to the sea as quickly as possible. "Storing more water in buffers, so that we can benefit from it during drier periods."

Better water quality

So about 40% of the world's population is currently suffering from a shortage of good-quality water. This is the case, during certain periods of the year, in India and China and in large parts of the US and Europe. In the Netherlands too we sometimes face water scarcity due to low water availability and poor water quality. For example, during dry summers when salinity increases, there is limited ability to use the water for irrigation of crops.

Will this percentage increase in the coming years because of climate change? Van Vliet and her colleagues are currently researching this. It is already clear that in areas where the population is going to increase, such as Central Africa, the demand for water will increase and its quality will decrease. In some parts of the world, such as China, quality is actually expected to improve due to population decline as well as improvement and expansion of water treatment plants.

More awareness needed

Van Vliet is looking forward to communicating the results of these studies to the general public, water managers and policymakers. She hopes this information will contribute to improving water quality. "There is still relatively little understanding about the effects of global change on water quality. We still have many questions, for example about the long-term health risks."

When there is too little water owing to drought or too much water owing to heavy rainfall, there are usually concerns about water quantity first, as it is the most noticeable issue. Van Vliet: "The impact on water quality is a less obvious problem and therefore gets less attention. Although, fortunately, awareness ofthis is growing."