Absolutely. Potato water makes any bread better. I use it in whole wheat yeast bread, too, to make a lighter, softer whole wheat bread.
You can use leftover mashed potatoes, or just bake a potato in the microwave and whiz some of it with water, skin and all. You can keep cooked potato in the freezer to use, too. I keep my potato water in a jar in the freezer and thaw as needed, then re-freeze. It makes a world of difference.
If you use butter and milk in your mashed potatoes and use that to make potato water, it makes extra good bread...