"Grainy" doesn't mean "too much water evaporated", it means "it crystallized". For caramelization in a pot on the stove, by the time you start getting any significant caramelization, virtually all the water has evaporated already. You need this to happen without the sugar crystallizing.
To prevent crystallization, add a second kind of sugar other than sucrose. Corn syrup is the most common thing to use in the US; invert sugar syrup is more widely available elsewhere.
I personally don't think that a candy thermometer is crucial for making caramel (some types of caramel, anyway). But if you're not experienced with the process, it really helps you identify the different stages and see what's going on.