Keep an eye on your pan; the best indicator of doneness is appearance, not time. Just before the syrup reaches the shade you desire, remove it from the heat; the caramel will continue to cook for a few more seconds.
Pour 1/2 cup water into a medium (2- to 3-quart) heavy-bottom saucepan. Add sugar. Cook over medium heat, gently stirring occasionally, until sugar is dissolved and syrup is clear.
Continue to cook, without stirring, until the syrup comes to a boil, washing down the sides of the pan with a wet pastry brush two or three times to prevent crystals from forming. Let syrup boil, gently swirling pan occasionally, until medium amber. Remove from heat.