The best hair for watercolor brushes is expensive "kolinsky," a kind of
sable. But you can do quite well with inexpensive brushes made of
synthetic material. You will know the difference by the price. A large
kolinsky brush of the finest quality requires a bank loan. A similar size
in synthetic material is about one-twentieth the price. I once purchased a
large, top-of-the-line kolinsky which has appreciated so greatly in value
that I am afraid to use it and keep it in a safe.
I use a flat brush one half inch across, and another small flat brush. I
use these two brushes for the majority of my painting. In addition I use
one or two round watercolor brushes in size four or five. That is really
all you will need. I store them in a round toothbrush container together
with a sharp pencil of medium hardness, such as an "HB" for doing the
drawing preliminary to painting. I also use an eraser which retracts like
a ballpoint pen, and is available in any art or drafting supply store.