Seewasserwerk Lengg

Beneath the bustling city of Zurich, a hidden marvel hums. The Seewasserwerk Lengg, a vital artery, quenches the thirst of an entire city. Built in 1960 and later modernized in 1975, the Seewasserwerk Lengg is a testament to human ingenuity. This water treatment plant, nestled in the Riesbach quarter, draws its lifeblood from the depths of Lake Zurich. It’s the largest and most important waterworks in Zurich, a silent giant working tirelessly. The Seewasserwerk Lengg boasts a maximum daily output of 250,000 cubic meters. This impressive feat is orchestrated from the Hardhof control center, ensuring a constant flow of pure water. The journey begins 500 meters from the shore, 32 meters below the surface of Lake Zurich. Here, in the cool embrace of the lake, where the temperature remains a constant 6-8°C, lies the intake. Six powerful pumps draw the water, capable of delivering up to 13,000 cubic meters per hour. To prevent pesky zebra mussels from clinging to the pipes, a monthly chlorine rinse keeps them at bay during warmer months. The Seewasserwerk Lengg’s process is a symphony of purification. From the depths of the lake, the water travels through a 1.6-meter diameter pipe. It journeys beneath the Tiefenbrunnen bridge, arriving at the plant 50 meters above. Inside massive filter chambers, the lake water undergoes a transformation. Ozone, a powerful disinfectant, is employed twice, eliminating viruses, bacteria, and even traces of medication. A charcoal filter further refines the water, removing any lingering tastes or odors. Next, a rapid filter of gravel and pumice removes suspended particles, creating a crystal-clear stream. The final purification step involves a slow filter of sand and gravel, 80 centimeters thick, ensuring no impurities remain. This entire process, from lake to tap, takes approximately eight hours. A unique feature of the Seewasserwerk Lengg is its live monitoring system. Rainbow trout swim in an aquarium filled with the treated water. A camera observes their every move, triggering an alarm if anything seems amiss. While some waterworks have switched to water fleas, which are even more sensitive to impurities, the trout at Seewasserwerk Lengg remain a reliable indicator of water quality. Interestingly, a significant portion of the filtration system lies hidden beneath the earth, concealed beneath nearby tennis courts, a testament to the integration of this essential facility within the city landscape.