Where waters are to be used in steam boilers this is not so important, but where it is to be used in the house for all kinds of domestic purposes, including drinking, it is an important matter. No process of chemical treating can be regarded as restoring water to an ideal condition of potability. No amount of sedimentation, for instance, will remove soluble sodium salts and completely remove sulphate of lime from solution. These bodies often give a distinct alkalinity to the water itself, which may amount to from thirty to forty parts per million. In such cases it is better not to attempt to secure a complete softening of the water, but only a partial one, since the original materials which make the water hard may be less injurious than the residual materials which come from a complete softening.