The close link between water supply, sewage disposal and public pools suggests itself. In the Tyrolean capital with its 125,000 inhabitants, however, the abstraction of drinking water is moreover closely related to power generation.

The city derives 99 % of its drinking water from 12 springs nestled into the hills surrounding Innsbruck. This water needs no conditioning (but is permanently monitored by the Sanitation Department of Innsbruck University) before it is delivered to the consumer.

The proportion of spring water in this area is quite high, even by Austria‘s top standards – a privilege which many other regions of the world will never enjoy. The springs tapped by IKB render a water volume of about 42 million m3 annually, which is 3.5 times the amount actually used.

The most prominent water resources come from the Mühlauer Quellen, covering 95 % of the overall demand. Water from these springs is completely germ-free, crystal clear, and odour-free, flowing from the mountain at a constant temperature of 4.5 °C all year long.

Its total hardness of 6–8 dH° is very low by karst-water standards. The water largely owes its excellent quality to the spring catchment area lying amidst the Karwendel National Park, where it is spared the potential impact of human settlement. Another advantage is that the water remains inside the mountain for more than a decade, during which it passes through a multitude of different geological layers and gets perfectly cleaned.

Double usage of water

Much technical foresight was already demonstrated in the 1950s, when the city authorities decided to build a 1.6-km-long man- accessible tunnel system to collect the drinking water from Mühlau. Organic building materials were entirely avoided and only decay-resistant reinforced concrete was used.

The water is drained from the mountain through a collecting tunnel and transported via two pressure pipes down to the Mühlau drinking water power station, situated at a level of 450 metres below; the power station renders 5 % of the electricity demand of Innsbruck. The turbines are designed with a view to preventing any quality impairment of the drinking water.

After this primary usage, the proportion actually used as drinking water flows into the 26,000-m3 Mühlau reservoir and further on to the 446-km-long supply network. According to IKB estimates, the average daily per-capita consumption is 262 litres. Currently 1.29 euros (net price) are charged for 1 m3 of water.

Since early 2006 a 1,260-m-long piping system has been in place, channelling the remaining amount of water into the new Naturstrom Mühlau power station. This has further increased the electricity output of IKB, which operates in all four large-scale hydropower units producing roughly half of the city’s annual electricity demand. The residual amount is purchased from Tiroler Wasserkraft AG (TIWAG).

IKB Chief Executive Harald Schneider reports that a safety concept was developed in 2004 to assure a safe water supply also in times of crisis, also taking account of a worst-case scenario in which the Mühlauer Quellen water would be completely cut off. “The resulting water reservoir management system using state-of-the-art control mechanisms enables us to optimally compensate such a cut-off by tapping water from other springs and from the groundwater resources of Höttinger Au.

IKB also lays emphasis on water resource protection programmes by designating protected zones in spring catchment areas, purchasing land in the immediate proximity of these catchment areas, and compensating land owners for any arising usage restrictions.”

Proper disposal, day after day

IKB’s motto in wastewater management is “proper disposal, day after day”. This is achieved through a combined sewer system about 400 km in length (250 km of sewage collectors), a state-of-the-art sewage treatment plant in Rossau and – last but not least – a seamlessly functioning flood management system.

How much it pays to consistently upgrade the sewer system with the latest technology was demonstrated during the flood events in August 2005: the sewer conduits of Innsbruck safely withstood the pressure of the water masses and, due to their increased flow capacity, were essential in relieving the situation. The flood water pumping stations, too, operated flawlessly.

The city’s sewage treatment plant, built in 1993/94 for 70 million euros, is designed to cope with a daily capacity of 165,000 m3 of effluents; it can therefore additionally take up sewage from 14 adjoining communities for processing. The wastewater undergoes a full-scale cleaning process comprising two consecutive treatment stages – mechanical and biological.

The result is impressive: according to IKB, 95 % of organic contaminants, 90 % of phosphorus, and more than 70 % of nitrogen are removed. The resulting digester gas goes to a block-type thermal power station where it is converted into electricity and heat.

“In 2004 alone, IKB spent 4.7 million euros on the extension and restoration of the city’s sewer system. This investment is now perfected by a modern sewer management system,” says Harald Schneider optimistically. After all, Innsbruck has a large city budget and political leaders who fully support the publicly run enterprise.

Innsbruck’s mayor Hilde Zach (from the political party “Für Innsbruck”), who in May was re-elected for another term of office, recently said in an interview: “It fills me with pride and comfort to know that our city’s water supply is in safe public-sector hands and works so well. Water is not just any commodity but a vital provision of immeasurable value for human wellbeing and health.”
(Source: aqua press Int. 2/2006, Mag. Christof Hahn)

Contact & Information:

Innsbrucker Kommunalbetriebe IKB
Salurner Straße 11, A-6020 Innsbruck
Tel.: +43/512/502-0