Washing is a feature in Nations that allows you to extract dye from colored Wool, and convert Concrete Power into Concrete.
Wool Bleaching: Right click a cauldron filled with water while holding colored (non-white) Wool. The cauldron will give back 1 White Wool, and 1 of the colored Wool's respective dye.
Concrete Hardening: Right click a cauldron filled with water while holding Concrete Powder. The cauldron will give back the respective Concrete block of the same colour.
A water amount equal to 1 Water Bottle will be consumed from the cauldron with each use.
Tip: To avoid placing the blocks down when using the Cauldron, stand as close to it as possible and click on the cauldron's side.
The dye removal process from Wool but also many other colored blocks can be automated in the Dye Extractor.