School starts and homecoming from vacations with suitcases full of dirty laundry. These weeks, households' water consumption is usually high, according to Alexandra Fleetwood, press contact at Stockholm Water and Waste (SVOA).
Many seem to have heeded last week's call to save water. The latest week has seen water consumption in Stockholm decrease by 15 percent. However, a strained situation for tap water persists, and the call to save water still applies this week.
It takes 5-6 liters of water per minute when you let the tap run, so don't waste unnecessarily, says Alexandra Fleetwood.
Temperature-sensitive purification
The main reason for the water shortage is an unusually high water temperature in Lake Mälaren, which disrupts the waterworks' purification filters. To purify drinking water, the waterworks at Lovön and Norsborg use biological filters with bacteria that are dependent on water temperature, according to Kenneth M Persson, professor at the Department of Technical Water Resources at Lund University of Technology.
A certain group of microorganisms that usually purify the water does not thrive in warm water. Then, organic material may leak through, and the bacteria need more time to purify the water, he says.
Purification is being expanded
In cases where biological water purification is applied in warmer countries, the filtration used is already adapted to the collection of bacteria that purify the drinking water, according to Kenneth M Persson. To avoid a shortage of tap water in the future, one must therefore expand and climate-adapt the capacity for slow filtration, he emphasizes.
Two new filters for slow filtration will also be put into operation in 2026, says Alexandra Fleetwood at SVOA.
Inspired by southern countries
In other parts of the country, water shortages are often due to low groundwater levels. Also, in these cases, Sweden should, according to Kenneth M Persson, be inspired by southern countries that are more accustomed to handling water shortages.
While we in Sweden adopted water purification techniques from Germany and the Netherlands in the 19th century, we should now be inspired by, for example, Singapore and Namibia, where wastewater is reused without being released into the environment in between, he says.
Even at the individual level, we should consume less water, he believes.
In Denmark and Belgium, the average water consumption is less than 100 liters per day. In Sweden, it is 140 liters per day.
The call to save tap water still applies in all of Stockholm, Huddinge, and neighboring municipalities that receive their water from Stockholm's waterworks in Lake Mälaren: Strängnäs, Nynäshamn, Lidingö, Nacka, Tyresö, Haninge, Botkyrka, Värmdö, Ekerö, and Salem.
Cooler weather does not affect the situation since the water is taken from deep in Lake Mälaren and transported for a short time, half an hour, which means that the water does not have time to cool down.
This does not apply, for example, to Sydvatten, whose waterworks in Eslöv supplies large parts of Skåne with drinking water and takes its water from Lake Bolmen in Småland. The water is a bit cooler there and is not affected in the same way by warming. It also has time to cool down since the transport time from the lake to the waterworks is a week.
Norrvatten, which supplies 14 municipalities north of Stockholm, including Solna, Sundbyberg, Järfälla, Vaxholm, and Norrtälje, with drinking water, uses chemical precipitation and carbon filtration to purify the water. That process is not as temperature-dependent as slow filtration.
Source: Norrvatten and Kenneth M Persson, Lund University of Technology.
