I bought this wonderful book by Karl Mårtens at, Konst & Folk Gallery. I really like karl's approach to watercolouring, a mixture of Zen Buddhism, Scandinavian simplicity, Japanese calligraphy and natural artistic talent. I had a look around on the internet and have not found it so you'll need to visit the gallery if you want to buy it.
Visit Karl Mårtens website here.
Konst och Folk
Tel: +46 8 644 60 60