Place sugar and water in a small saucepan over medium heat.
Bring the sugar mixture to boil and bubble.
When the sugar mixture has turned into an amber colour, turn the heat off. *1
Add hot water in two different times and swirl the mixture by holding the saucepan handle. *2
If you are going to use this sauce for Japaneses pudding(Purin), pour it into the pudding forms straight away before it becomes harder.
Notes
*1 Once the sugar mixture starts to change colour, do not take your eyes off the saucepan. Caramelised process will be very quick and may burn. *2 Even if you add hot water, it will still splash so be careful.