LahdenpohjaThe greater Helsinki area is supplied with drinking water via the Päijänne water tunnel. With a length of 120 kilometres, it is the longest continuous rock tunnel in the world. The constant temperature conditions found deep in the bedrock maintains the water’s good quality throughout its long journey. Asikkala The rock tunnel starts from Asikkala at the southern end of Lake Päijänne, and ends in a vertical shaft near Pitkäkoski water treatment plant in Helsinki. The Vanhakaupunki and Pitkäkoski treatment plants take in their raw water from the shaft. The Päijänne tunnel is connected by a branch tunnel to the Silvola buffer reservoir. Hämeenkoski The Päijänne tunnel is excavated at a depth of 30–100 metres in the bedrock. The head differential between the tunnel ends allows a discharge rate of about 10 m3/s. The present rate of water intake by the treatment plants is about 2.7 m3/s.