I’m not an expert, so maybe someone can say if this might be a valid theory, but could it be that the weight of the water for a prolonged period has caused some pipe to come loose or something like that?

Hence the word “probable”

Yeah it’s not dangerous to just open it for a second to smell. The handle looks to be blue though, so i’d wager it’s more probable to be water and keep a bucket under it.

No, no, no you’re onto something

Generally flooring like this is laid along the longest wall. If there isn’t one, it’s up to you. Just make sure you measure it out beforehand so you won’t end up with a last plank being 10cm or something. Same goes for the width. If you end up with the last one being a few cm, it’s better to start with half a plank.

A big part is also getting the inside water out.

I’m not an expert, but I believe it’s more to do with them being in one position for very long, so it wouldn’t matter in what position that would be. As long as you turn them open and then close them again once every few months, any calcium buildup would break loose. Maybe someone who is an expert can back me up :)

Hoo boy you must be insanely glad you caught this when you did.

It might be helpful to know what kind of walls you have. What is the material, do they have space that can be filled with insulation material?

I’m amazed at the concrete on top of it as well. Normally (in my house) it would be the other way around.

Yep that’s exactly what it is.

600 gallons for 17 dollars? That’s very high to me. We pay about 1€ per 1000L, so 600 gallons would cost about 2,20 euros.