They aren't using the same water for a week. The GP comment is nonsense.

Wait until you hear about 38y and more soy sauce from China or broths (with meat and fish) that cooked for years in Korea in the same pots.

Edit: That makes sense, but using the same water for whole week at a time seems a bit disgusting to me. Even if it is boiled quite often.

Sorry I wasn't able to edit it.

In a restaurant that makes pasta as a focus you don't "boil it quite often", you boil it constantly. Many gallons of boiling water takes forever to come up to temperature, and once it's there the pot can be thermally insulated to keep it there above 200F with minimal additional heating. Customer orders, you dump it in, customer is served in 5-15 minutes.

You keep it at a slow boil, and properly salted, all day long. If you're using it more than one day, you'd probably want to keep it hot overnight, like "perpetual stews", but I can't attest to how common this is, especially in restaurants that aren't constantly plating pasta.

You can manage it as a batch process, throwing the water out when it gets too starchy, but doing this unaided leaves you unable to use the water as emulsifier at the start of the cycle. You could also do it as a perpetual process by pouring some off the top and refreshing with clean water.

What? What is gross? Did you ever saw raw meat? It's probably gross. There are also insects walking over your vegetables. Gross.

Gross part is that you are boiling same liquid in open space where people are working and making a mess. Also you are going to accumulate residue ar the bottom. Unlike meat or vegetables this can't be washed.

Do you find it gross when there's a big stockpot simmering stock for 12 hours without a lid in order to reduce?

And what's to wash? You don't wash food after cooking, and pasta is like bread -- it certainly doesn't need washing beforehand either. It's just flour and some other ingredients.

It's not like vegetables where you need to wash off dirt, pesticides, etc. Or meat where you wash off bacteria. Those aren't issues with pasta.

I do not. I didn't make myself clear in first comment. Sorry for that. I was talking about using same water for a whole week. I felt that it is not optional. The residue building at the bottom, open space of messy kitchen with lid open and constant reheating because it cools overnight is what seems little bit off for me.

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.

If it’s constantly at a boil I doubt there’s a food safety issue though high volume pasta shops probably don’t need to keep the water more than a day

Ahhhhhh, I also misunderstood your comment. Yeah, I hear you. Maybe you can keep the starch water in airtight container...not sure. I don't keep starch water for the next time I'll cook pasta. I just use the currently made starch water to create a sauce. Highly recommended! But, as mentioned in the research, wait for the water to cool down a bit. Or make a risottata in a pan. <- also highly recommended if you have a pan big enough.

I guess you don't wash flour, but it does need to be disinfected (eg by cooking it) - it's a little unsafe to eat raw, which is the problem with raw cookie dough.

If there was a way to get rid of the insect eggs people would presumably want to do it too, but iirc they're just too small to filter out.