Pour 1 cup of the water into a medium bowl. Sprinkle 2 Tablespoons unflavored gelatin powder over the water and allow it to hydrate, about 5 minutes.
Meanwhile, mix 6 Tablespoons lemon juice and 6 Tablespoons granulated sugar together in a heat-proof measuring cup. Add enough water to make 1 cup of liquid in total (you will need approximately 1/2 cup of water). Heat in the microwave on high heat until very hot and steaming, about 1 1/2 to 2 minutes.
Pour the hot lemon juice mixture over the gelatin mixture and stir until dissolved, about 1 minute. Pour into an airtight container or into individual bowls and cover with plastic. Place into the fridge to set. Allow to chill fully, at least 2 hours.