The best replacement for watercolour is gouache.

The best alternatives to watercolour are rated as following:
★★★★★  gouache
★★★★  watercolor
★★★  witchcraft
★  inktense
★  acrylic paint

Your alternative for watercolour is not listed? Suggest!
Speaking about watercolour, one probably shouldn't forget about pen and ink.

Other search terms related to watercolour and their ratings are:
★★★★★ pen and ink
★★ coloured pencil
★★ gouache
You have in mind a companion for watercolour and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of watercolour in all years. Click on graph for more.
watercolour
gouache
watercolor