Replacement of the Gönhard reservoir in Aarau

Jul 20, 2022

New DN 400 drinking water transport pipeline

Gerechtigkeitsbrunnen – or Fountain of Justice – in the Kirchplatz in Aarau [Source: EADIPS®]

Aarau – the capital city of the canton

The city of Aarau is the capital of the canton of Aargau and, geographically speaking, lies at the Northern edge of the Swiss Mittelland region at the transition to the Jura mountains, about half way between Basel and Zürich as the crow flies.

Some world famous personalities were born in Aarau or had their home here. The best known of these were the nutritionist Max Bircher-Benner, who invented muesli, and Nobel prize winner Albert Einstein who was educated at the Canton school in Aarau.

Water supply for city and suburbs

In 1947, with the merging of the city’s own electricity and waterworks with the gasworks, which at the time was under private ownership, the Industrielle Betriebe Aarau IBA came into being. In 2000 the company became independent and changed its name to IBAarau. The city of Aarau today has a majority shareholding of 95 % in the public limited company with holding structure.

IBAarau is to undergo organisational change and as from 2018 will appear under the new name Eniwa. With more than 320 employees, IBAarau today supplies the city of Aarau with electricity, natural gas, district heating/cooling, electric power services and drinking water, which comes exclusively from groundwater, is conveyed from three pumping stations and is stored in three reservoirs.

The drinking water is fed into the network round the clock without processing or additives as a pure natural product. Together with the residents of Aarau, the population of the surrounding suburbs of Küttigen, Unterentfelden, Erlinsbach and Eppenberg-Wöschnau – plus to some extent Schönewerd and Gretzenbach – are supplied with extremely high-quality drinking water.

Site plan showing the old and new Gönhard Reservoir [Source: IBAarau]

Operational building of the old Gönhard reservoir [Source: EADIPS®]

In addition, there is an emergency water supply for the adjacent municipalities of Aarau nach Buchs, Suhr and Oberentfelden.

The cityscape of Aarau is still today characterised by more than 70 public wells, which is a sign of a well-functioning water supply. Superb quality drinking water can be enjoyed from these wells “fresh from the pipe“ at any time without any misgivings.

Pipe store in the Gönhard Forest [Source: EADIPS®]

The route of the pipeline alongside a field track [Source: EADIPS®]

Project for the new Gönhard reservoir

An analysis of the current state of the Aarau water supply infrastructure in the context of a “General water supply project (GWP)” in 2014 revealed that all three existing reservoirs – Gönhard (constructed 1941), Oberholz I (constructed 1899) and Oberholz II (constructed 1916) – are in need of renovation. In addition, their storage volume is too small to cover the long-term water requirement expected.

A new reservoir concept, which was developed by IBAarau as a result of these findings, envisages replacing the present Gönhard reservoir by a larger reservoir and, once this is put into operation, dismantling the three old reservoirs (Gönhard and Oberholz I and II).

The new Gönhard water reservoir, as a “project of the century”, will ensure the long-term supply of clean and healthy drinking water to coming generations in the region of Aarau. From an economic point of view, combining the necessary water capacities in a single new and centrally located water storage facility will increase efficiency in terms of both operation and maintenance.

The construction of the new central Gönhard reservoir will ensure that the natural resource of water is sustainably managed for future generations.

New DN 400 drinking water transport pipeline

ECOPUR pipe – layer structure with PUR coating/lining [Source: EADIPS®]

In the run-up to the construction of the new reservoir, which was commenced in Summer 2017, in order to maintain the supply of water an additional DN 400 drinking water transport pipeline had to be laid. Thanks to this back-up main supply pipeline there is now sufficient drinking and extinguishing water available at all times within the Aarau supply area.

The following deadlines are planned:

  • Construction of the transport pipeline February to June 2017 
  • Construction of the reservoir July 2017 to September 2019 
  • Dismantling of the old reservoirs subsequently

The construction work for the new transport pipeline was able to be tackled on schedule in February 2017 and it started right at the location of the new reservoir in Gönhard Forest, a popular local recreation area on the outskirts of the city of Aarau.

The route of the pipeline runs alongside a path in the forest area – from Sennweg via Höhenweg, the old Distelberg road – to the start of the built-up area of the city of Aarau.

In the last stage of construction, the DN 400 drinking water pipeline will be installed in a residential district until it connects up with the pipeline network in the Goldernstraße. This last part of the pipeline construction project will be carried out in 2018 in collaboration with the city of Aarau, when the construction of other pipelines (gas, electricity, telecoms) is scheduled.

Looking forward to the further progress of the project, the drinking water transport pipeline will also continue on until it turns into Kantonsstraße/ Entfelderstraße so that, during later renovation work, it can be connected to the drinking water supply network and the residential quarter will not be further affected.

For the new water transport pipeline, IBAarau is putting its trust with conviction in ductile iron pipes of the vonRoll ECOPUR type with reinforced coating to EN 545 [1].

Assembling a HYDROTIGHT push-in joint with hydraulic pipe-laying equipment [Source: EADIPS®]

Installation under difficult conditions where pipelines cross [Source: EADIPS®]

The full-protection pipes with integral polyurethane lining and exterior coating which have been tried and tested over decades can be used even in highly aggressive soils without any further protective measures. And the HYDROTIGHT restrained push-in joint guarantees simple and secure handling of the cast iron pipe system as well as very efficient assembly.

Minor directional changes in the route can be handled by the angular deflection inherent to the push-in joints. For more major changes in direction, for branches etc., a complete range of fittings is available.

vonRoll ECOFIT type fittings are coated with epoxy resin to EN 14901 [2] and in accordance with the enhanced requirements of RAL GZ 662 [3].

The use of ECOPUR ductile iron pipes will make sustainable and secure operation of the new main supply artery of the regional water supply in and around Aarau possible for decades to come.

MK 45° bend installed [Source: EADIPS®]

Stock of fittings at the construction site [Source: EADIPS®]


With the new Gönhard water reservoir the long-term supply of clean drinking water in the region of Aarau will be secured. To this end, an additional DN 400 drinking water transport pipeline has been constructed. Thanks to this back-up main supply pipeline there is now sufficient drinking and extinguishing water available at all times within the Aarau supply area.

For the new water transport pipeline, IBAarau is putting its trust in ductile iron pipes of the vonRoll ECOPUR type with integral polyurethane lining and coating which can be used in soils of any level of aggressiveness without further protection measures.

With the HYDROTIGHT restrained push-in joint, simple and secure handling as well as very efficient assembly of the cast iron pipe system is achieved.

[1] EN 545 Ductile iron pipes, fittings and accessories and their joints for water pipelines – Requirements and test methods 2010
[2] EN 14901 Ductile iron pipes, fittings and accessories – Epoxy coating of ductile iron fittings and accessories (for increased loads) – Requirements and test methods 2006
[3] RAL GZ 662 quality and test requirements Schwerer Korrosionsschutz von Armaturen und Formstücken durch Pulverbeschichtung [Heavy duty corrosion protection of valves and fittings by powder coating] 2008-01
Roger Saner
vonRoll hydro (suisse) ag von 
Roll-Strasse 24 
CH-4702 Oensingen 
Phone: +41(0)62 3881237 
Development, planning and construction 
IBAarau Trinkwasser AG 
Obere Vorstadt 37 
CH-5000 Aarau 
Phone: +41(0)62 8350040 



European Association for Ductile Iron Pipe Systems · EADIPS®/ Fachgemeinschaft Guss-Rohrsysteme (FGR®) e.V.

Dipl.-Ing. Christoph Bennerscheidt

Managing Director

Doncaster-Platz 5

45699 Herten



+49 2366 9943905


+49 2366 9943906



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