I was clarifying because a lot of non water soluble cone vs. water soluble cone lists, has it listed as "slightly soluble". It is water soluble in the bottle, when mixed with certain other ingredients, but not after being applied to hair. After which you do need SLS, ALS, cocamidopropyl betaine, or coco betaine to remove it. Some low poo's contain even milder ingredients which won't remove it.
But I do agree that a cone is either water soluble or not, when speaking of whether or not water will remove it from hair (like we care if it disperses in water in the bottle or not.. we just want to know how it effects our hair!).