It is not a good idea to leave your watercolor brushes sitting in water or to seal them up after using them. Eventually, the enamel will begin to crack, chip and flake off. This does not mean it's the end of a good brush. Don't through it away, don't stuff it in a drawer never to be used again.
Simply take masking tape and wind it around the handle of the brush where the enamel has begun to chip and flake off. This will help extend the life of a brush tremendously.
When I first started taking watercolor painting classes, I did not take good care of my brushes. After class I would pack my stuff up, often times tossing my brushes into a ziplock bag. I did not seal the bag, but I left the brushes in the bag. I never left my brushes soaking in the water.
When I used the brushes at home, I would place them in a cup, bristle end up. The water would soak through the ferrel and into the handle of the brush. I believe this is what caused the tip end of the handle to crack and chip off.
After class as soon as I get home I now open up my brush holder and after using my brushes at home, I allow my brushes to air dry flat. This method has definitely extended the life of the enamel on the brushes.
And yes, the taped yellow brush does have the end tip sawed off. This helps it fit in my travel case.