Saving cooking water is not economical. Has not many nutrients in it either if pasta or potatoes were cooked in it (would have some good stuff if say asparagus or greens were cooked in).

Vegetable scraps on the other hand are gold. Cabbage cores, broccoli /cauliflower stems, kale/collard green stems. Also meats that don't look too appealing (but are not spoiled) do well in soups.

Parmesan rinds is perfect in pasta sauces.