CERN consumes a considerable quantity of water to cool its accelerator complex. At the same time, the Organization also releases water into the neighbouring watercourses, many of which are small and thus sensitive to the quality of the water they receive.

In 2018, the last year of accelerator operation before LS2, CERN consumed some 3.5 million cubic metres of water, which corresponds to around 1400 Olympic-sized swimming pools. The majority of this water comes from Lake Geneva. In the same year, CERN discharged 5.1 million cubic metres of water (this figure includes infiltration water pumped from the tunnels and release of precipitation run-off) into watercourses and wastewater treatment plants.

Given these large quantities, responsible water management is of the utmost importance to CERN.

The Organization’s approach to water management is focused on two areas: minimising water consumption and optimising the qualitative and quantitative aspects of the water released into watercourses.

CERN’s water consumption has decreased drastically since the beginning of the millennium, with the yearly consumption decreasing from 15 million cubic metres in 2000 to about 3.5 million cubic metres in 2018, a major reduction of about 77%. A key contributing factor to this achievement has been the upgrade of the SPS cooling circuit from open to semi-open, enabling the recycling of water and considerably reducing the need for fresh water input. Following this example, efforts are ongoing to change from open to semi-closed or closed cooling circuits. In this context, CERN has set itself the formal objective of limiting the increase in water consumption to 5% until the end of 2024 (baseline year 2018), despite a growing demand for water to cool upgraded and new facilities such as the High-Luminosity LHC.

The reduction of water consumption is leading to a decrease in releases to neighbouring watercourses, such as the Nant d’Avril in Switzerland and the Lion and the Allondon in France. CERN’s HSE unit runs a monitoring programme on effluent water quality and quantity and regularly samples the watercourses to evaluate CERN’s impact on these small and thus very sensitive watercourses. The HSE unit reports to the Host State authorities about the results of the monitoring programme on a quarterly basis.

Several initiatives have been taken to improve the effluent water quality. One of them involves using demineralised water in the cooling towers in order to decrease chemical treatments that affect the water quality and to decrease the quantity of water released into the watercourses. During LS2, the main cooling towers on the Meyrin site were upgraded to this end and other upgrades will follow in the coming five years.

Another example of CERN’s water management strategy is the construction in 2020 of a retention basin near the Prévessin site. The basin will retain and, under certain conditions, regulate water from rainfall flowing off the Prévessin site into the Lion in order to retain incidental pollutants.

You, too, can contribute to CERN’s efforts to optimise the effluent water quality by not throwing pollutants (e.g. chemicals) or other waste (e.g. cigarette butts) down the drains, which discharge the effluents directly into the rivers.

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This article is a part of the series “CERN’s Year of Environmental Awareness”.