Few subjects have attracted more attention among sanitary reformers, than the necessity of obtaining a copious supply of water to the dwellers in large cities. Experience has shown that the supply should be at least twenty gallons daily for each inhabitant, although forty gallons are necessary to carry out to the full extent all the sanitary improvements deemed desirable for the well-being of a population. But in looking to quantity of supply, quality has been thought of less importance; there could not be a more gross error, or one more fatal to civic economy and domestic comfort. As we are anxious to instruct the readers of this Journal in the science of every-day life, we propose to consider the subject of water-supply in some detail, and in the present article to explain the serious inconveniences which result from an injudicious selection of hard water for domestic purposes. The water found in springs, brooks, and rivers, has its primary origin in the rain of the district, unless there should happen to be some accidental infiltration from the sea or other great natural reservoirs. This rain, falling on the upper soil, either runs off in streams, or, percolating through it and the porous beds beneath, gushes out in the form of springs wherever it meets with an impervious bed which refuses it a passage; pits sunk down to the latter detect it there, and these form the ordinary wells. In its passage through the pervious rocks, it takes up soluble impurities, varying in their amount and character with the nature of the geological formations, these impurities being either mineral, vegetable, or animal matter. The mineral ingredients may be chalk, gypsum, common salt, and different other compounds but it is the earthy salts generally which impress peculiar qualities on the water.