Why You Can't Substitute Pasta Water With Fresh Water - Chowhound

As you boil pasta in salted water, it releases starch into the liquid. It's a process you can actually see happening as the pot simmers and the water becomes cloudy from all the dissolved starch. In fact, all that starch is the reason why, when you add pasta water to a sauce, it thickens up as the starch molecules swell up and bind to water. Also, if you were to add it to an oily sauce (which nearly all pasta…