Waters may often be of such a character that the process of softening necessarily leaves in the water a number of precipitated materials. Water of this kind should always be allowed to settle; in other words, be carried to sedimentary basins before it is used. In this way gravity will speedily clear the water, since the precipitated matters are always considerably heavier than the water itself. This process, however, does not care for the soluble materials which are left in the water, chiefly compounds of sodium. Thus the actual state of the water in some cases after softening may be worse for potable purposes than it was before.