Spray the slow cooker insert with cooking spray and place ham inside.
Combine honey, brown sugar, mustard, cinnamon, and nutmeg in a saucepan over medium heat. Cook, whisking thoroughly, until sugar is melted and ingredients are combined, 2 to 5 minutes. Remove from heat.
Pour water into the bottom of the slow cooker. Pour sauce over the ham. Cover.
Cook in the slow cooker on Low, 6 to 8 hours. Baste the ham with the juices from the bottom once every hour.
Remove ham from the slow cooker. Pour juices from the bottom into a saucepan over medium heat. Mix cornstarch and water together in a bowl and pour into the saucepan. Cook until mixture thickens into a glaze, 6 to 8 minutes. Pour glaze over the ham or use as a gravy.