Minecraft wiki entry for Achievement_guide, associated text: You can fill cauldron using water bucket, rain, or glass bottle. For dye, you can obtain it from flowers, cactus, lapis lazuli, cocoa bean, bone meal, ink sac, or by combining multiple dyes. Then dye water by adding it to the cauldron. Lastly, press use at cauldron filled with dyed water while holding leather armor.