Explanation Behind the Water Shortage Alarm in Stockholm

Residents of Stockholm are being urged to conserve water. However, in nearby Solna, which also sources water from Lake Mälaren, no such warning has been issued. So, how has Sweden's largest municipality found itself in the midst of a water crisis?

– It's not about neglected maintenance, says Christian Rockberger, CEO of Stockholm Water and Waste.

Last Friday, Stockholm Water and Waste raised the alarm about a "strained situation in water production." To ensure the water supply lasts, everyone in Stockholm and eleven neighboring municipalities were asked to reduce their water consumption.

Media reports have described the situation as an acute water shortage, but it is actually about limited capacity.

"Not a Shortage of Raw Water"

Or, as the engineering consultancy firm Sweco describes it:

"The problem is not a shortage of raw water (the raw material for drinking water, editor's note) in Lake Mälaren, but that the waterworks are struggling to purify enough when the water becomes too warm."

The company continues:

"This is a clear example of how climate change challenges our societal systems and why we need to build robust infrastructure and solutions that can handle new conditions."

According to Christian Rockberger, CEO of the municipal company Stockholm Water and Waste (SVOA), Stockholm has "one of the most robust water systems in the country."

And the warning issued last Friday was unusual, he says.

Why Stockholm Residents Should Conserve Water

The reason the company felt compelled to appeal to residents for help is due to "two interacting factors":

– One is that Lake Mälaren has been unusually warm, and wind conditions have pushed the warm surface water down so that even at eleven meters deep, it has been four degrees warmer than normal for this time of year. This disrupts our purification process, says Christian Rockberger.

Technically, it concerns the final step in the purification process, which is when the water flows through the slow filter (see fact box above). If the water is over 15 degrees, the growth of certain bacteria increases significantly, explains the SVOA CEO.

– This creates a different balance in this purification step, and some of the filters become unusable and must be disconnected.

– We could have managed this if it hadn't coincided with one of our high consumption periods, when Stockholm residents return from the countryside before school starts and need to do laundry. We also have a large daytime population working in Stockholm.

Difference from Solna and Täby

It was in the middle of last week that SVOA noticed the production capacity of the waterworks starting to decline, prompting them to issue their warning. However, residents in the northern municipalities of Stockholm County, such as Solna, Järfälla, Sollentuna, and Täby, have not received the same call to conserve.

They get their tap water from the producer Norrvatten, which also sources its raw water from Lake Mälaren – but has a different waterworks.

– They have the Görväln plant, which is located in a different part of Lake Mälaren, and their high consumption periods are different, says Christian Rockberger.

The Görväln plant also has two different intake depths for raw water, depending on the season and water quality, which can mean access to cooler water. Stockholm only has varying intake depths at Lovön – between 5 and 30 meters – while in Norsborg, it is always 11 meters, the CEO explains.

– There are technical possibilities that we do not have at the Norsborg waterworks today.

"Reasonable to Help Each Other"

Why don't you have that?

– This problem has not arisen before. But we have accounted for it when planning for future water supply. We have an investment program that includes a deeper raw water intake, but there are long lead times for such things, so the solution will be in place in five to ten years at the earliest.

There has been talk of climate change and the risk of warmer summers for a long time, so how could you not foresee this situation?

– I think we have anticipated it in the long term with the investment program we have. But when such factors interact, which can occur every five to ten years, it may also be reasonable to help each other and conserve water. It may not be reasonable to design for all conceivable events that only occur every ten years, although we should, of course, build as robust a system as possible.

Criticism of Maintenance

At the same time, SVOA believes that this type of event may become more common.

Even Svenskt Vatten believes that Stockholm residents, like other Swedes, will have to get used to water warnings due to warmer lakes.

– It's like much else related to climate change, says CEO Pär Dalhielm to SVT.

He continues:

– In the long term, we need to consider where in Lake Mälaren the intake of drinking water is and what type of technology is used to produce and deliver the water. It all boils down to the need to finance Sweden's future water supply. We often say that Sweden has a huge investment gap to fill in water supply.

He has also, in general, highlighted the need to maintain water infrastructure.

But the strained water situation in Stockholm is hardly due to that, according to SVOA.

– This situation is not about neglected maintenance but about warm water in Lake Mälaren and it being a high consumption period, says Christian Rockberger.

So how will you handle warmer water in the future?

– In addition to deeper raw water intakes, we are also planning for a new waterworks and reviewing different purification techniques.