We need advanced water treatment methods to remove not only more, but also more complex, substances to ensure clean drinking water in the future. This is the view of DTU Professor Hans-Jørgen Albrechtsen, who conducts research into our drinking water.
In fact, half or more of Danish water wells examined for contamination contain undesirable chemicals that have seeped into the groundwater. Since 1999, over 300 water wells have actually been closed down due to contamination.
Some of the substances that threaten groundwater—and our health—are nitrate and xenobiotics such as pesticides and biocides, which are used to combat insects and weeds and to prevent the growth of microorganisms in, for example, paint and wood materials.
Due to stricter requirements for the acceptable content of PFAS in drinking water, PFAS is now also found in such high concentrations in the groundwater in several places that it is necessary to treat the water using advanced technologies and processes. This poses a challenge to the waterworks, which must ensure that the tap water remains safe to drink.
“Many people mistakenly believe that our drinking water has remained untouched in the ground for decades, ready to be sourced and drunk. But this is, unfortunately, a misunderstanding. And precisely this misunderstanding means that we’re not ready to treat the water to the extent necessary in the future,” says Hans-Jørgen Albrechtsen.
Harmful to nature and people
Some of the most hazardous xenobiotics in our groundwater belong to the PFAS group of synthetic chemical substances, which have, for example, been used in electronics and the production of plastics, paints, and textiles since the early 1950s. The substances are suspected of being endocrine disruptors and carcinogens, and they are difficult to break down in nature.
PFAS substances have, for example, been used in industry for impregnation and surface treatment of metal, wood, and textiles. PFAS compounds originating from industrial pollution are also found in the air where they are borne by the wind over long distances until they fall to the ground when it rains, with a subsequent risk of seepage into the groundwater. Decomposition products from pesticides are also frequently found in the groundwater.
As researchers become better at screening and developing new environmental analysis methods, new sources of contamination are also emerging, says Martin Hansen, Associate Professor at DTU. Together with his colleagues, he has developed sensitive non-target analysis methods to help prevent that potentially hazardous contaminants are overlooked. Such methods can identify thousands of previously unknown substances. Most recently, the researchers have found traces of anti-epileptic drugs and other medicinal products when they examined the groundwater using this method in collaboration with the Danish Environmental Protection Agency.
Significant footprint
“We see human activities on the earth’s surface leaving a fairly significant footprint and negative impact on the groundwater. At the moment, a lot of resources go into finding out if we can resolve these problems through water treatment. And, fortunately, this is possible for most substances. But some of the substances that occur relatively frequently—such as DMS (degradation substance from fungicides, ed.)—are cumbersome and difficult to remove, but, in turn, they aren’t particularly health hazardous,” says Hans-Jørgen Albrechtsen.
In his opinion, it is difficult to start a discussion at political level about whether we should spend a lot of money and resources on water treatment for some relatively unproblematic substances, and whether we have the right threshold values—or whether some of them should be increased.
He therefore calls for an overall water strategy for ensuring clean drinking water now. A strategy that both protects the groundwater and develops and implements water treatment technologies for handling the current contaminations at the waterworks. But even if measures are taken to offer total protection of the groundwater now, it will take 30 to 60 years before the new, clean groundwater resulting from the strategy will reach the water well.
We can still drink the water
Fortunately, there are many measures we can take to ensure that we also have good and healthy tap water in the future. According to Liselotte Clausen, Chief Consultant at Greater Copenhagen Utility (HOFOR), there is a need to tighten the regulation of the use of chemicals, clean up old soil contaminations that could otherwise seep with rainwater down into the groundwater, treat the drinking water for unwanted substances, and protect the groundwater with groundwater parks, which are selected areas that are protected against pesticides and other toxic substances.
Today, HOFOR faces two major challenges. One challenge is the substance DMS, which HOFOR finds almost everywhere in the extraction areas. DMS is a degradation product from fungicides which has been used both as a biocide in paint and as a pesticide for fruit and berry growing. The second challenge is a significant PFAS contamination found in the extraction area of Solhøj Kildeplads, which is HOFOR’s largest source site (an area where extraction wells are placed, ed.).
HOFOR has therefore tested five different water treatment technologies to compare their efficiency and water quality. One of the technologies is activated carbon, which is a filtration method that binds harmful substances such as PFAS, pesticides, and biocides to the surface. DTU has contributed to the test set-up by examining the extent to which another of the water purification technologies—the so-called resins—adds undesirable substances to the treated drinking water, and how you can prevent a resulting deterioration of the drinking water quality.
The findings show that all the tested technologies effectively remove the worst PFAS substances. Now HOFOR will assess the sustainability of the tested technologies and choose the final water treatment method for full-scale implementation.
“We’re looking into a future where I’m convinced that we can continue to drink water directly from the tap, but something needs to be done now in terms of stricter regulation of chemicals, groundwater parks, and development of treatment methods,” says Liselotte Clausen.
Development and innovation
DTU participates in several development and innovation partnerships in which researchers contribute significant knowledge about the chemical behaviour of PFAS and how the substances are transported and dispersed towards the groundwater.
One of these partnerships is called InSa-Drikkevand, which is a drinking water innovation partnership between ten of Denmark’s largest water utility companies and DTU. One of the focus areas under the partnership is to examine xenobiotics such as pesticides, biocides, and PFAS in the groundwater and understand how they are broken down. The goal is to ensure that drinking water is produced in a sustainable and socially responsible manner. The partnership will bring together the water utility companies’ actions and initiatives to ensure future clean drinking water based on groundwater.
In another collaboration, three DTU professors and seven other experts are members of a PFAS knowledge task force that the Danish Government set up in 2023. The knowledge task force will set the direction for the Danish PFAS activities. The aim is to gather knowledge about the occurrence, risks, and dispersion of PFAS in the environment in Denmark and internationally in order to limit human and environmental exposure. Says one of the task force members, DTU Professor Poul Løgstrup Bjerg, and adds:
“In recent years, the discovery of PFAS in the environment has given rise to concern in the population. By being part of the task force, DTU can contribute to ensuring that technical knowledge is added to the risk assessment of PFAS when evaluating causes of contamination. In this way, we can help focus on areas where new knowledge is needed and provide specific instructions for action aimed at reducing PFAS exposure for ordinary people, municipalities, and regions.”
