I regularly have the pleasure of demonstrating to Art Groups. I usually start by informing members of the equipment I am using. If it is a watercolour demonstration I emphasise the importance of the surface upon which you choose to paint.It is possible to do a reasonable sketch on almost any paper – although, of course, the paper may not last long. Similarly, if you are doing a quick watercolour sketch to record, for reference, some detail, tones or colours, all sorts of paper will suffice.
If, on the other hand, you want to produce your ‘best’ work with ‘maximum’ control, and you want it to last, you need a quality paper especially produced for watercolour painting.
Again and again I emphasise to groups that quality paper is essential. You can get away with ‘student quality’ paints, which you can apply with a variety of tools (there are certainly excellent brushes available at very reasonable prices), but you cannot get away with poor quality paper – so if you are working to a limited budget buy quality paper, and look to make the savings on the paint and brushes.