Heat recovery from shower water - is it sensible?

I came across during research that there are heat recovery systems for shower water (e.g., in the drain channel). Does anyone here use this? It could be that the acquisition and installation costs call the economic viability into question...

Without having installed it, this is mostly my own assumption for now:

We need about 10 to 12 kWh per day for hot water. I estimate and say that about 60% of that is used for showering.
Assuming one would install something like this and somehow manages to recover 50% of the heat, that would be about 3.6 kWh per day.

With gas, I currently pay 7 cents per kWh. So about 25 cents per day or roughly 90€ per year.

However, this assumes that the system is installed in all the showers used.

There was someone in the forum a long time ago who praised such a pipe heat exchanger for showers to the highest degree and also installed it in their own home. In total, there were then two homeowners. Since then, it has become quiet again about the matter.

There was a user here before who built with the same general contractor as I did. The general contractor had advised against it. We did not install it - too uneconomical. That was in 2017. The reasoning has already been provided by .

If you care about ecology, simply use less water. You probably just need to run the water for a few seconds less or set it slightly cooler for the same savings.

Turn off the water while soaping, should also save quite a bit. Water and soap!

Washing makes the water dirty! !

ergo ?