tarev, as long as you're boiling the mixture on the stove, that how a lot of sources recommend to do it. Just don't microwave a mixture. I've seen sources that say you don't have to boil it at all, some say you can also boil the water, then add sugar. I don't really know which is better. My sugar does dissolve quickly in hot water, so I do heat part of the water...or all, if I'm only making one cup.
