@seekermoc Romans had indoor plumbing and running water over a thousand years ago it's hardly a modern invention. Since their metallurgy of the armor is full plate, which was common in 13th century, this level of plumbing tech is no big deal. Also the glassware is more impressive, as it's super expensive super secret tech in Europe historically, especially CLEAR see through glass, but the shop gives them away by the hundreds just as potion packaging? I'm guessing it's some magic cheat otherwise the shop would have asked about a container buy back of the glass to discount the next potion purchase.
Here a wiki link on Venetian glass
https://en.wikipedia.org/wiki/Venetian_glass
Edit: now that I think about it the large clear shop windows in the first chapter are tech that looks like it could be float glass that was only invented in 1950 or maybe Fourcault process which was used in the early 1900's
I remember some history person remarking that before the computer age was the glass age, it really is a ground breaking tech we take for granted.
Answer: isekai MAGIC!
