From the mountains to the city: Vienna's drinking water lifeline
The uninformed observer could be forgiven for thinking that Vienna gets its drinking water from the River Danube - an integral part of the city for centuries. Instead, 97% of the city's water comes directly from the Styrian and Lower Austrian Alps nearly 200km away via two long-distance mains, and is so pure that it only requires basic chlorination before entering the distribution network. Once in the network, the Vienna Waterworks makes sure that the bulk of it reaches consumers taps, reducing leakage rates in the city to below 10%. Thanks to Dipl.-Ing. Walter Kling of the Vienna Waterworks for helping compile this article.
The Klaffer Spring above ground
Two spring water mains from mountain springs in the Rax-Schneeberg and Hochschwab ranges deliver around 97% of Vienna's total water. Operated by the Vienna Waterworks, the mains - a series of shafts, aqueducts and brick-lined supply channels -allow Alpine spring water to flow by gravity into a network of 34 reservoirs in and around Vienna.
The first of the two mains from Kaiserbrunn to Vienna was inaugurated in 1873 by the Emperor Francis Joseph I. Approximately 120km long, the main collects water from a variety of springs in the Schneeberg and Rax area, the Kaiserbrunn spring in the H”llental valley, the Stixensteiner spring and the Pfannbauern spring which alone has a daily maximum output of 26,000m3.
At an altitude of 795m, the Pfannbauern spring has an extremely regular output of 300l/sec. Water temperature at the source ranges from 5.5 to 7.5oC.
In total, the first Vienna Alpine spring water main guarantees the supply of a maximum of 220,000m3/d of mountain spring water to the city.
The second main from Wildalpen to Vienna was officially opened in 1910. With a total length of 192km, the second Vienna Alpine spring water main transports water from springs in the Styrian Salza valley and the Hochschwab range to Vienna.
Supplying 234,000m3/d, the second main consists of over 100 aqueducts and 19 culverts built to bridge or underpass valleys and rivers. Mountain water takes 36 hours to reach Vienna. The springs that feed the second supply line (the Brunngraben, Hollbach, Kläffer and Siebensee springs near Wildalpen as well as the Schreierklamm and Säusenstein springs) meet approximately half of Vienna's daily water requirements.
Water distribution in the city
Facilities available to the Vienna Waterworks include 32 reservoirs in Vienna and two outside of the city with a total storage capacity of about 1.5Mm3. The company also operates 10 pumping stations and 11 pressure control plants.
The Vienna mains system consists of about 3200km of pipes with diameters ranging from 50mm to 1200mm. In addition to the distribution mains, the system also includes domestic service connections equipped with water meters which supply about 100,000 customers. Mountain water is chlorinated before it enters the distribution network in the city.
Drinking water quality is monitored by Vienna's Institute of Environmental Medicine. Water supplied into the distribution mains is controlled daily and the catchment areas of the first and second Vienna Alpine spring water mains are controlled and monitored continuously.
Groundwater: Vienna's water supply in perspective
Based on a breakdown of annual water consumption, the Vienna Waterworks has analysed water requirements for the period 1960 to 1993 and drawn up a forecast of future water demand. According to this forecast, the city will require an additional volume of water of at least 17,000-40,000m3/d by the year 2010.
Groundwater reserves remain important for Vienna even though there is an abundant supply of Alpine spring water. Instances when the city has to fall back on these reserves include times when flow from the springs is low or when the Alpine spring water mains have to be taken out of operation for maintenance and repair work.
Groundwater also acts as a valuable reserve against natural disasters or a large-scale pollution incident. Damage to the infrastructure caused by mudflows can entail interruptions in the supply of spring water. In such cases, groundwater reserves guarantee the uninterrupted supply of drinking water to the city.
The Lobau groundwater works, with a maximum capacity of 60,000m3/d, was built to complement the water supply provided by the two aqueduct systems. In the last few years, use of the facility has been confined to situations when repairs had to be carried out on the two aqueducts, in cases of major pipe ruptures, and in times of extremely high water consumption during periods of excessive heat.
With the expansion of the groundwater works in the lower Lobau and at Moosbrunn as well as the construction of a new WTW for the well-fields at Nussdorf and in the northern region of the Danube Island, the Vienna Waterworks is aiming to increase the capacity of its groundwater works to such an extent that it will allow the company to replace one of the two Alpine spring water mains if needed. A third Vienna water main - a 16km long delivery main from Moosbrunn to Vienna - will soon be taken into operation.
With a view to generating the additional volumes of water required up to the year 2050 and based on currently available information on water quality, the Vienna Waterworks is also involved in long range planning such as a general survey of the sources of water available in the entire range of the northern limestone Alps.
The Viennese authorities are also considering setting up an integrated supra-regional supply system.
Preventing water loss in Vienna
The Vienna Waterworks has its own separate data transmission system, which covers the entire operating area up to the springs in the Alps and allows the company to control the network remotely. This system is one of the key instruments for fighting water loss.
Databases provide exact information about the network as well as leakage statistics. Indications of possible leaks are usually discovered during regular maintenance checks as well as through loss analyses and reports from local residents.
Several methods can then be used to precisely locate leaks in the supply system. These include:
Volume flow measurements by means of permanent or temporary water meters.
Measurement of leak noise levels using acoustic sound locators or leak noise correlators.
In addition to a weekly external inspection of the Alpine spring water mains, leaks can be pinpointed by inspecting the mains from within when they are completely emptied for maintenance - at least twice a year. Drainage pipes at the base of slopes may also indicate where leaks are located and in aqueducts, damage is easily detected by watching out for water seepage.
Leak detection efforts in Vienna have proved their worth. Over the last 25 years, leakage figures have been reduced from about 25% of the volume of water fed into the network to only 8-9%.
The Bisamberg reservoir
Built in 1995, Bisamberg is the newest reservoir in the Viennese network. With a capacity of 60,000m3, the reservoir was built to improve the security of supply, to cope with peaks in demand and to reduce fluctuations in water pressure in an area to the east of the River Danube.
The reservoir is built in water-tight reinforced pre-stressed concrete and consists of two identical chambers separated by a central gangway. With the construction of Bisamberg, Vienna's 21st and 22nd districts now have their own mains reservoir, obviating the need for spring water to be piped across from the right bank of the River Danube.
Vienna's water supply: facts and figures
The Vienna Waterworks supplies 1.6M people with drinking water. Average consumption is 390,000m3/d.
Each city resident consumes 150l/d of water on average.
97% of the water supplied is Alpine spring water. The remaining 3% comes from groundwater and surface water.
Along the long-distance mains, the Vienna Waterworks operates 12 power plants which produce about 60M kWh of electricity.
The water can be stored in 34 reservoirs with a total capacity of 1.5Mm3 - more than three times the usual reserve requirements.
The total length of Vienna's mains system is 3200km.