|1863||On December 3, the city council of the city of Essen agrees on building the first water catchment facility in the Ruhr valley.|
|1864||On October 20, the waterworks in Essen starts operating.|
|1867||The waterworks in Witten starts operating.|
|1880||More than 100 waterworks are being set up in the Ruhr valley between 1880 and 1900.|
|1883||Robert Koch discovers the bacterium causing cholera, which is being transmitted via drinking water.|
|1897||Annual water abstraction from the Ruhr amounts to 135 million cubic metres.|
|1899||Waterworks and power plant operators found the Ruhrtalsperrenverein as a voluntary association.|
|1901||A typhoid epidemic breaks out in Gelsenkirchen. Robert Koch, acting as a consultant on the disease’s containment, speaks out in favour of establishing an institute for hygiene, which until today is located in Gelsenkirchen.|
|1903||Annual water abstraction from the Ruhr amounts to 197 million cubic metres.|
|1904||The Fürwigge Reservoir stars operating on March 24, the Ennepe Reservoir on December 5.|
|1906||On December 6, the decision is taken to build the Möhne Reservoir. Construction starts on January 7, 1908.|
|1910||Dr. Karl Imhoff, who will later become managing director of the Ruhrverband, draws up the report "Keeping the Ruhr clean".|
|1911||Drinking water conditions along the Ruhr are catastrophic during this extremely dry year. A typhoid epidemic breaks out in Mülheim, infecting 1,500 people. Annual water abstraction from the Ruhr rises to 412 million cubic metres.|
|1913||An act on keeping the Ruhr clean (Ruhrreinhaltungsgesetz), based on Imhoff's report, is being published in the Prussian law gazette on June 5, creating the legal basis for sewage treatment along the Ruhr, of which the Ruhrverband takes responsibility. |
Enacted on the same day, an act on the Ruhr reservoirs (Ruhrtalsperrengesetz) controls water quantity management along the Ruhr and turns the Ruhrtalsperrenverein into a public body.
The Möhne Reservoir is inaugurated on July 12, constituting at that time the largest reservoir in Europe.
|1925||The first sewage treatment plant in continental Europe with activated sludge treatment starts operating in Essen-Rellinghausen.|
|1929||The Ruhr region goes through another extremely dry year. In order to avoid the catastrophic consequences of such weather conditions in future, the construction of several repump stations, designed to transport water from the River Rhine up to Essen if needed, is being initiated. Lake Hengstey is the first out of eight planned impounding lakes to be finished. According to Imhoff’s plan on how to keep the Ruhr clean, they are designed to foster the river’s natural purification.|
|1931||Lake Harkort is the second impounding lake of the Ruhr to start operating. |
Construction of Lake Baldeney starts right during the world economic crisis as a so called emergency measure, meaning that most of it is done through manual labour. In peak times, up to 2,000 unemployed find work on the construction site. The largest impounding lake of the Ruhr, with a surface of 2.65 square kilometres, is completed in 1933.
|1934||Dr. Karl Imhoff, since 1922 managing director of the Ruhrverband, is forced into retirement by the National Socialists. Throughout the country, he is considered the most important expert on sewage engineering and also enjoys international recognition. |
After eight years of construction, the Sorpe Reservoir starts operating. The construction site of its 700-metre-long dam was at times the largest construction site in Europe.
|1938||On December 20, the decision to build the Bigge Reservoir is taken. 19 years, however, go by until construction starts, another eight years until the reservoir is finished.|
|1939||The start of the Second World War disrupts construction of the Verse Reservoir which had only started a year before. During the war, construction is taken up again and carried out resorting to forced labour from inmates of the labour education camp Hunswinkel. Around 550 of the camp’s prisoners die from hunger, abuse or shooting during the war. The Verse Reservoir can only be completed in 1951 after 13 years of construction. The Hunswinkel camp disappears under the water when the lake is impounded. Today, a memorial at the Klamer Bridge commemorates the victims' suffering.|
|1943||In the night from May 16 to May 17, a British bouncing bomb tears a hole into the dam of the Möhne Reservoir. 1,500 people die in a flood wave up to seven metres high. The Eder Reservoir in Northern Hesse is also being destroyed during this night. The Sorpe and the Ennepe Reservoir, however, resist the bombing sustaining only minor damages.|
|1947||Extreme droughts cause the water to retreat to an alarmingly low level. The series of repump stations has been completed up to Lake Baldeney and provides people along the lower Ruhr with water from the Rhine.|
|1949||The Ruhrtalsperrenverein celebrates its 50th anniversary with a ceremony at the Verse Reservoir.|
|1955||A mechanical sewage treatment plant starts operating in Duisburg-Kaßlerfeld.|
|1958||A two-stage biological sewage treatment plant goes into service in Essen-Werden.|
|1959||Once again, a dry year leads to water shortages. The situation is worsened by the fact that the Sorpe Reservoir has been completely emptied to repair the damages of war. |
The series of repump stations along the Ruhr is being extended by three more stations up to Bochum-Dahlhausen. The repump stations in Winz, Hattingen and Blankenstein, however, are never completed; the planned stations Herbede I and Herbede II never realised.
|1963||The coal crisis - already developing since the late 1950s - comes to its first peak when 13 mines are being shut down. The closures mark the end of the region's mining tradition lasting over two centuries. The consequences can still be felt today. Groundwater infiltrating the gigantic network of pits and tunnels stretching underneath the entire Ruhr region has to be pumped off around the clock - a continuous challenge of water management in the region.|
|1964||In late 1964, an act on detergents comes into force as a result of the increasing usage of detergents containing tensides from the mid-1950s, causing heaps of foam to appear on rivers and streams. It stipulates that detergents may only contain tensides which are at least 80 per cent biodegradable. |
The Central Detoxification Plant (ZEA, today Central Disposal Plant) goes into service in Iserlohn. It takes care of the pre-treatment of liquid wastes, which in the early years mostly came from the region's metalworking industry and its crafts enterprises.
|1973||The increasing load of nutrients such as phosphor and nitrogen in the Ruhr leads to massive algae growth. The excessive growth of plants affects drinking and industrial water treatment, puts the fish stock at risk and causes the lakes to silt up. |
Dr. Hans Werner Koenig, managing director of the Ruhrverband and the Ruhrtalsperrenverein, publishes a memorandum on the "rising threat to drinking water supply from the Ruhr". In his exposé, he explains that in future, water supply can only be safeguarded if it goes hand in hand with water management and land use planning measures. Koenig is particularly worried about the increasing degree of soil sealing.
|1975||The Ruhr Water Quality Report (today Ruhr Quality Report) is being published for the first time. From this year on, it appears annually, consistently monitoring the continuous improvement of the Ruhr's condition.|
|1978||The Ruhrverband increasingly uses effluent polishing ponds for tertiary treatment in its sewage treatment plants. The largest effluent polishing pond with a surface of 360,000 square metres is being completed at the sewage treatment plant in Bochum-Ölbachtal.|
|1979||Lake Kemnade goes into service on August 1. It is the fifth and last of originally eight impounding lakes to be created along the Ruhr according to the plans of Dr. Karl Imhoff. Since sewage treatment has meanwhile improved significantly, Lake Kemnade is from the beginning not primarily built to reinforce the river's natural purification but mainly for recreational purposes.|
|1983||After 50 years in service, Lake Baldeney is being excavated to keep it from silting up. An overall 1.1 million cubic metres of sediment are removed from the lake and transported to two spoil areas in the Heisinger Aue floodplain.|
In November, the Henne Reservoir only reaches one fifth of its filling level at maximum impoundage. Old streets and bridges appear in the dried-up areas.
|1986||The Rahmedetal sewage treatment plant starts operating the Ruhrverband's first aeration system with targeted denitrification.|
|1990||Based on a law enacted on February 7, the Ruhrtalsperrenverein merges with the Ruhrverband, so far responsible for water quality management. From July 1, the new water association takes on the name Ruhrverband.|
|2000||Elodea nuttallii, an aquatic plant native to North America, appears in Lake Harkort. In the following years, it spreads to Lake Hengstey, Lake Kemnade and Lake Baldeney. Stronger plant growth is facilitated by the rising water quality of the Ruhr. Since the water has become much cleaner in recent years, sunrays can now filter through to the ground. But the plant affects water sports and other activities. Therefore, the Ruhrverband tries to find a long-term solution, for instance through a research project supported by the North Rhine-Westphalian Department for Environment. Until today, however, all attempts to get a grip on the plant have been rather unsuccessful.|
|2003||On March 21, the Ruhrverband opens the "Historical Collection of Ruhr Water Management" inside a former gas transfer station next to the sewage treatment plant in Essen-Rellinghausen. It serves professional training purposes and is also open to guided tours.|
|2005||The Ruhrverband concludes its 1.5-billion-euro investment programme with the new construction of the sewage treatment plant Essen-Süd. Since 1990, this money had been used to modernize all sewage treatment plants in a way that they can to a large extent retain phosphor and nitrogen.|
|2007||On January 18, a storm named "Kyrill" sweeps across Central Europe with winds of up to 225 kilometres per hour, causing desastrous damages, especially in the Sauerland and Siegerland regions. In the Ruhrverband's forests alone, around 400 hectares of trees fall victim to the storm within only a matter of hours. The reforestation of this area, mainly with oak and beech, takes two and a half years.|
|2009||Bei einer Kontrollbefischung der Ruhrfischereigenossenschaft und des Landesamts für Natur, Umwelt und Verbraucherschutz werden im Juni mehr als 20 reinrassige Junglachse in der Ruhr bei Mülheim-Raffelberg entdeckt. Lachse waren seit über 100 Jahren aus der Ruhr verschwunden. Ihre Rückkehr ist das Ergebnis eines nachhaltigen Wassermanagements, mit dem die Qualität des Ruhrwassers in den vergangenen Jahren kontinuierlich verbessert wurde.|
|2016||Das Ruhreinzugsgebiet verzeichnet zwischen Juli und Dezember die trockenste zweite Jahreshälfte seit Beginn der Aufzeichnungen im Jahr 1927. In jedem einzelnen Monat des Halbjahres fällt weniger Niederschlag als im jeweiligen Monatsschnitt, im Dezember sogar nur 30 Prozent der Durchschnittsmenge. Selbst im extremen Trockenjahr 1959, in dem die Behörden zur Schonung der Wasservorräte das Autowaschen und Rasensprengen verbieten mussten, gab es im gleichen Zeitraum einige Liter mehr Niederschlag. Die Folge: Ins neue Jahr 2017 starten die Talsperren des Ruhrverbands mit dem geringsten Füllstand seit 20 Jahren.|