Old swimming pool serving as water reservoir
When the city of Arnhem built a new swimming pool, it was faced with the question of what to do with the old pool. Before long, the idea cropped up to use it as a water reservoir to collect rainwater. During periods of drought, the water that is collected can be used for watering municipal greenery.
Idea for a water reservoir
The idea for using the old Valkenhuizen swimming pool as a water reservoir was mainly prompted by the dry summers of 2018, 2019 and 2020, which were quite hard on the greenery in the city. The municipality of Arnhem has ambitions to plant more greenery, among other things to provide more cooling and to boost biodiversity. For that reason, a solution needed to be found for such periods of drought: how could sufficient water for the greenery be ensured? Thus, the idea arose to use the old swimming pool for rainwater storage.
How is the water reservoir being used?
The old swimming pool was converted into a water reservoir with a storage capacity of some 5 million litres of water. Rainwater falling on a total of 6,000m2 of new and existing rooftops is collected and stored via a separate rainwater sewer. Once the reservoir is filled to capacity, an overflow pipe conducts the excess water to an existing infiltration basin. In periods of drought, the water stored in the water reservoir will be used for the greenery in the neighbourhoods surrounding the swimming pool and for the sports fields.
What are the benefits of the water reservoir?
The new water reservoir has several advantages:
- More economical use of water: no or reduced need to use surface water or groundwater to water neighbourhood greenery, and less groundwater needed to water the sports fields.
- Reuse of resources: the old swimming pool is repurposed and does not need to be demolished.
- Less transport needed: the greenery contractor can now use the local water reservoir for watering the greenery, rather than driving all the way to the river. This saves many journeys through the city.
- Smart use of space: the reservoir roof has been converted into a car park, thus leaving room for other designations such as greenery at other locations.
Is the water reservoir producing the desired effect?
The exact effects of the water reservoir still need to be explored. Will it hold sufficient water for periods of drought? And what extent of water savings will it yield? The municipality of Arnhem will be measuring such effects in the years ahead.
More expensive than planned
The project turned out to be more expensive than initially estimated, due to the irregular construction method that had been used for the old swimming pool. This required additional measures to be carried out to provide the car park on top of the reservoir.
Lessons to be learned
The following lessons can be learned from the project:
- Convincing the owners and users of the sports fields proved the most difficult part. Everyone is in favour of sustainable measures, but preferably at no cost. Using groundwater as was done previously was easy and cheap.
- In 2024, the quality of the water stored in the reservoir was examined and assessed as “good”. Initially, however, the chloride content was found to be too high – though this water could still be used to water the sports fields. Most probably, the chloride originated from the old swimming pool tiles. The water is now sampled for quality on a monthly basis.
Incentive scheme grant
This project was co-funded with a EUR 118,000 grant from the Climate Adaptation Incentive Scheme.
Contact person
Ronald Bos
Gemeente Arnhem
ronald.bos@arnhem.nl