Children splash happily in the water, diligently practise with water wings and race down the slides, while parents enjoy the pleasantly warm whirlpools to relax. None of the visitors to Therme Wien has any idea what is going on a few metres below them: the waste water is not wasted but reused to generate district heating for around 1,900 households in Oberlaa, saving around 2,600 tonnes of CO2 annually.
Here you can read the article (in German): https://science.apa.at/reportage/die-waerme-aus-der-therme-zur-abwaermenutzung-von-thermalwasser/