Acrylic paint is a pain in the butt to get out of your paintbrushes if left to dry even for a little while. If its not taking over the whole brush and turning it into a spear you could skewer frogs with, it gets into the ferules and makes the working bristles stiff after a while. Nothing really will take it out, right??? Wrong! Alcohol. Rubbing Alcohol :) Check it out... I bet it revives watercolor brushes, too. Give it a try and post your results in the comment area.
Hugs and best wishes of creativity,
Linda