Pasta isn't the only starchy dish where one should consider reserving some of the water from the boiling process. As it turns out, potato water has some great benefits, too.
Real Simple says potato water allows the more solidified mashed potatoes to loosen up and achieve the perfect texture. The New York Times Cooking also explains that potato water creates a creamy, fluffy texture without adding many other ingredients.
Little House Living says that the starch in the potato water makes it an ideal thickening agent that could quickly bulk up things like sauces, gravies, or stews. The Gardening Cook also explains that it will not only hydrate the soil but also "spur the release of plant nutrients."