1. Chop the chocolate into small pieces, or use chocolate chips.
2. Set up a double boiler, and bring the water to a simmer.
3. Add 2/3 of the chocolate in the top of the double boiler, and bring melting chocolate to the following temperatures, stirring constantly. Remove from heat once you reach the respective temperature (1 or 2 degrees off is OK). Continue stirring off the heat if chocolate isn't completely melted.
Dark: 115 degrees F
Milk: 110 degrees F
White: 105 degrees F
4. Add the remaining chocolate to the melted chocolate a little at a time, stirring constantly, until all the chocolate is melted. Try to keep the mixture at the following temperatures, bringing it back to heat if the temperature starts to drop too much (again, 1 or 2 degrees off is OK).
Dark: 89 degrees F
Milk: 85 degrees F
White: 85 degrees F
Make sure the temperature of the chocolate stays within 2 or 3 degrees of the cooler temperatures while you're using it, using a heating pad if necessary. If it gets too hot or cold, it will lose temper, and you'll have to start over.