Bring water to a simmer.

Whisk in chocolate chips until chocolate is completely melted.

Fill a bowl with ice cubes and place the pot over the ice or pour the chocolate into a bowl and place that over ice.  Using a whisk, hand blender, or standing mixer, whisk mixture until a mousse texture forms.

Once you achieve mousse-like consistency, stop mixing; if you over mix the mousse will harden. Pour into bowls or ramekins and let set. Eat immediately or refrigerate until ready to serve, it should sit for 2-3 days. 

Note: If you overmix and it gets grainy or hard, simply melt it again and whisk it more carefully.  If it doesn't thicken at all, melt it again and add some chocolate then follow the directions again.