In a saucepan, combine the water with the grated ginger. Bring to a boil, then simmer, uncovered for 20 minutes.
Remove from the heat, and using a fine-mesh sieve or cheesecloth, strain out the ginger pulp, reserving the remaining liquid. You can place the remaining ginger pulp in ice cube trays for ginger stir-fries or smoothies.
Combine the ginger liquid with lemon juice and maple syrup. Per serving, to a large glass, add ice, then 1/2 cup to 1 cup of the ginger liquid, followed by 1/2 cup to 1 cup of the sparkling water, depending on desired strength of the ginger ale. Stir and enjoy immediately.