According to the UN and Sweden’s environmental objectives it is important to attain a high water quality and a sustainable use of freshwater. More and more people are currently moving out to the archipelago, which increases the use of freshwater on the islands, especially during summer when guests tend to visit as well. Runmarö is an island in Värmdö archipelago where the residents currently only have individual wells and sewage systems. Runmarö is more vulnerable to disruption of the freshwater, compared to the mainland, and if a groundwater shortage were to happen during the summer, it would be a big concern.
Using the surface water from one of the island’s lakes could be an alternative to the use of water. The largest lake on the island is named Viträsket and is located on the southern part of Runmarö. Since cold temperatures might affect the water pipes negatively, it is more appropriate to use the seawater from the lake during the summer. In this report it is examined whether seawater can be used as a water supply on Runmarö and if Viträsket is an appropriate water source. For the seawater to be used on the island, the residents will have to form a community facility.
Literature studies were conducted to understand the prerequisites on the island and what further investigations could be carried out in this report. A field study was also carried out on the island where residents were interviewed about Runmarö’s current water situation and their thoughts about seawater and community facilities. The tap water was also tested at the interviewee’s homes. A test from Viträsket was collected as well to get a grip of its water quality. Bo Olofsson and Erni Bergenstråhle contributed with existing data of different wells on Runmarö. During the field study, Bergenstråhle was also interviewed about whether it is reasonable to use community facilities and seawater on Runmarö.
If the water samples collected from Viträsket and the water taps has a higher percentage than Livsmedelsverket recommends for a certain substance, it could be possible to drink the water, but one should be observant. Only two of the tap water tests had a percentage lower than Livsmedelsverket’s limits. The other tests had at least one substance that exceeded the limit. Lake Viträsket had a high percentage of culturable microbes that exceeded Livsmedelsverket’s limit. These microbes are not suitable to consume over a longer period of time.
The interviewed residents were all open to join a community facility, they do however prefer it if someone else brings up the question and organizes the start of the process. Runmarö’s interest group handles the infrastructure issue on the island among other things. They might therefore be able to organize the process of creating and building a community facility. The seawater from Viträsket can be used for things such as the laundry machine, dishwasher, shower, toilet and irrigation without further cleaning. To be used as drinking water, it needs to be cleaned and cooled down, otherwise it might affect a person’s health negatively. From a technical point of view, it is more reasonable for the residents living close to Viträsket to use the seawater from Viträsket. Also, it is important to investigate how the water pipes would affect the wildlife around Viträsket. Furthermore, calculations on how much water Viträsket can supply and how many households that can use Viträsket as a source of water needs to be conducted.