There are systems that replace the shower drain with something like a heat exchanger, the water is warmed with the drain water right away, no need to store the

There are systems that replace the shower drain with something like a heat exchanger, the water is warmed with the drain water right away, no need to store the heat. For example https://www.oeko-energie.de/shop1/de/eco-shower-duschrinne.html https://www.oeko-energie.de/shop1/de/eco-shower-duschrinne.h... (in German, but the image is simple to understand.)