Coat a cooling rack with nonstick spray and set it in a half sheet pan lined with parchment paper.
Peel the ginger root and slice into 1/8-inch thick slices using a mandoline. Place into a 4-quart saucepan with the water and set over medium-high heat. Cover and cook until the ginger is tender, about 35 minutes.
Reserve 1/4 cup of the cooking liquid before transferring the ginger to a colander to drain. Weigh the ginger and measure out an equal amount of sugar. Return the ginger and 1/4 cup water to the pan and add the sugar. Set over medium-high heat and bring to a boil, stirring frequently. Reduce the heat to medium and cook, stirring frequently, until the sugar syrup looks dry, has almost evaporated and begins to recrystallize, approximately 20 minutes.
Transfer the ginger immediately to the cooling rack and spread to separate the individual pieces. Once completely cool, store in an airtight container for up to 2 weeks. Save the sugar that drops beneath the cooling rack and use to top ginger snaps, ice cream, or to sweeten coffee or tea.