Heat peanuts, sugar, and water in a 12-inch skillet over medium heat, stirring occasionally, until sugar is grainy and crystallized, 15 to 18 minutes. (Sugar should not caramelize.)
Raise heat to medium-high, and continue to cook, stirring constantly, until sugar just starts to melt again. (Sugar will start to caramelize. Adjust heat if sugar begins to burn or smoke.) Sprinkle with 1 1/2 teaspoons salt. Once peanuts are coated, with some crystallized sugar remaining, transfer to a parchment-lined baking sheet; spread into a single layer using a rubber spatula.
Transfer sheet to a wire rack, and let stand until cool and hardened, about 30 minutes.
Nuts can be stored in an airtight container for up to 2 weeks.