Simple question: turn off the water...

I wanted to try to replace the lever mixer in our shower because it is dripping and I can't reach the seal. I have already bought a new one. Now I looked to see where to turn off the water in our basement (yeah yeah, embarrassing :D). Around the water meter there is a turn screw in front and one behind it. Which one do I have to turn off or if both, in which order?

BTW: I think I can leave these adapter threaded parts on the shower lever and transfer them to the new lever, right? There are also threaded parts included that I probably do not need.
j.

It is enough if you turn off one of the two shut-off valves. There are two so that when your water meter needs to be replaced, it can be shut off from both sides. For your purposes, however, it is sufficient to stop the water supply. You can also keep the adapter threads as they are if everything fits like this. But if you have to turn them, I would be cautious about the tightness. In that case, I would rather seal the new ones well, and you will have peace of mind for now. Although, looking at the picture, I have to say, the rest of the bathroom could also use a renovation. ;)

Although I have to say about the picture, the rest of the bathroom could also use a renovation.

I also see a bunch of mold spores there, at least that's what I suspect. What else could it be? You seem to have a water problem, and from your previous posts, it also seems to be your property?! :(

Thanks, ok.. That's more or less what I thought, that one wheel should be enough.

Yes, I posted the picture of the faucet because the grout actually seems to have mold spores (another problem). How do you get rid of that? Can you just spray some mold remover on the tiles/grout and wipe it off later? Ventilation isn’t so easy for us. We ventilate often, but family members also shower a lot. Somehow, ventilating probably isn’t enough in the long run.
j.

My wife occasionally used the mold spray in the shower area of the old apartment as well. However, it did not look like that. Ventilation: On the one hand, you should place a hygrometer in the bathroom. In addition, you should emphasize to all family members to open the windows after showering/drying off. A quick airing for 10-20 minutes should be enough to reduce the humidity to a "normal" level. I was amazed at how quickly you reach a high humidity (> 85%) while showering, after I placed the hygrometer in the bathroom.

And don't forget to leave the shower door open. Otherwise, all the ventilation is pointless.