Oh, I see - yeah I've never heard of a restaurant using the pasta water across days. I don't think that's a thing. In fact it's a whole thing about how the pasta gets better throughout the day, because you start with fresh water each day. And remember that water is constantly being added to the pot as it gets soaked up by the pasta.

Just from a food safety perspective I'm not sure it's legal to reuse across days, given that it's going to take all night to cool, only just in time to be reheated again.