Denmark’s drinking water supply is unique, as it is entirely based on groundwater without the addition of disinfection chemicals such as chlorine. Water treatment at a Danish waterworks typically consists of aeration and filtration, which removes naturally occurring ammonium, iron and manganese. However, in the last few decades, groundwater in some places has been found to be contaminated with industrial chemicals, nitrate from agriculture, heavy metals and, lately, pesticides. With the growing population in Denmark’s capital city and the increasing pressure on groundwater resources, two of HOFOR’s most important tasks are ensuring a robust, reliable and safe water supply for the long term, while protecting aquifers from contamination and depletion. HOFOR achieves these tasks via an extensive system for monitoring the water quality, and the preservation of forests that serve as a shield against contamination of the aquifers.

Marbjerg is one of the largest waterworks in Denmark, and it supplies the Greater Copenhagen area with 4.8 million m3 of drinking water every year, equivalent to the water usage of 120,000 people. In the design of Marbjerg Waterworks, protection of the environment and the drinking water has been the main focus. Firstly, Marbjerg Waterworks is located in Himmelev Forest near Roskilde. The forest plays an essential role in protecting the area’s groundwater resources from pollution. HOFOR, together with Roskilde Municipality, has co-financed the purchase of the forest area, where the Danish Nature Agency is establishing a new forest that will permanently protect the aquifers from pollution from industry, agriculture and other activities. Secondly, the waterworks has been modernized so that the treatment processes are automatically controlled, and the water quality is monitored online. Furthermore, HOFOR has a strong focus on the materials that the drinking water is subjected to, both at the waterworks and in the distribution system. In fact, HOFOR has appointed a “committee for materials in contact with drinking water”, whose main goal is to ensure the right choice of materials in order to minimize potential migration of chemical or organic substances to the drinking water.

The drinking water is purified and transported exclusively inside pipes and sealed tanks. This means that the water is completely isolated and contained until the consumer turns on the tap, considerably reducing the risk of bacteriological contamination of the drinking water. Additionally, above-ground stainless steel tanks are used to store drinking water instead of the traditional underground concrete tanks. This way, leaks can be detected and repaired quickly. The new waterworks also uses pumps and machines that protect the environment by emitting as little CO2 as possible into the atmosphere.

Marbjerg Waterworks ensures a robust drinking water supply for current and future generations. Preserving good water quality in the aquifers by protecting the surrounding forest and utilizing thoughtful design and choice of materials has been key to achieving this goal.