Providing water to Karlskrona's residents has always been a concern. There were approximately 150 wells on Trossö, but the water in them wasn't good due to saltwater intrusion. Water was transported by barges from Lyckeby, and rainwater was collected.
In the late 1800s, a water pipeline was laid from Lyckeby, and Vattenborgen (the "Water Castle") was built as a water tower on the highest point of Trossö. In 1939, another water tower was constructed on Bryggarberget.
Vattenborgen has also served as a ventilation shaft for the military facility located beneath the square, and the building has housed various operations, including a restaurant and a museum.