Drawing is very important when it comes to working in the medium of watercolor, erasing can also be an important part of that drawing skill. Doing it wrong can ruin a perfectly good piece of expensive paper.
There are 2 different kinds of erasers, one is the hard rubber type and the other is a kneaded rubber eraser.
There is also the
eraser on the end of the pencil, I don't recommend ever using that eraser on watercolor paper because they tend to be very hard erasers and usually do damage to the paper instead of erasing.
Both types of erasers can be used in watercolor but not for the same purpose.
Use a kneaded rubber eraser on the pencil lines or to get some of the graphite off the watercolor drawing. this kind of eraser is soft and will not wreck and scratch the surface of the paper.
It would only wreck it if the paper were wet.
Never use the hard rubber eraser on the paper surface, it will ruin the surface if you rub to hard and even sometimes by just erasing, especially when the paper is a soft paper.
Another use for the hard rubber eraser is rubbing across a dry painted surface to take away some of the paint. At times if you use it on a dry surface it will get you down to the white paper, but don't expect to paint on that rubbed surface
anymore, it won't take the watercolor like a non-rubbed area of the paper would.
Check out the video below, to learn a trick on how to get the graphite off your drawing without getting rid of your pencil lines.