'I purchased this for my daughter who is taking GCSE art. There is a nice range of colours (but no white) and the white plastic box they come in is sturdy.'
My inner watercolour geek could not resist adding a comment..........
Traditional watercolour techniques do not use white and this is why many sets do not include it. Watercolours are by nature transparent; this is their unique quality & adds to their beauty. It is this transparency that gives the colours their vibrancy. It also enables them to be layered, creating many exciting effects. If white is added to the paint, it becomes dull, opaque & flat & is then, little different to gouache.
The key to creating lighter tones is not to add white, but to add water to dilute the paint & allow more of the white of the paper to show through. There are, of course, many sets, such as the one above, which do include white, but I would strongly recommend that you work on developing the techniques (& self-restraint!) to create lighter tones without it's use. Your work will have a clarity & vibrancy that is impossible to achieve by other methods.
PS. If you look closely at the photo above, you will see that my brush has never touched the white paint in this box!