Reserving a pasta cooking water instead of dumping the whole thing out is a common habit for home cooks and professional chefs, since the starches in the water are excellent at thickening and emulsifying sauces. Potatoes are just as starchy as pasta, so the water left over after boiling potatoes shouldn't be wasted, either.

Just like pasta water, potato water can be reused in the kitchen in a variety of ways. If you’re making mashed potatoes, you can substitute a bit of the milk or cream with the starchy water to thicken the texture, and the same goes for gravies and sauces; this is even better if your potato water is a bit salty, which adds some flavor.

Starch can also be used in the preparation of fried foods, and adding a splash of potato water to your batter will help it get extra-crispy in the hot oil. Potato water can even firm up pie filling, as long as it isn't soggy or cloudy, and the starches in potatoes are also filled with beneficial minerals and vitamins, including vitamin C and B6.