This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Of recent years the importance of insuring the purity of drinking water has become more and more appreciated, and an intelligent public is now aroused to the absolute necessity of protecting their supplies of drinking water from contamination with sewage, decomposing animal matter, etc. So general has the interest in this subject become in this country that new laws are being passed constantly to protect the water supply of large cities and towns. The subject is not confined to water alone, but includes ice as well, for many of the germs and organic impurities of water are not destroyed by freezing, and impure ice added to pure water contaminates it. It has been very clearly proved that many infections may be conveyed through the agency of water; among the most important of these are the germs of typhoid fever, dysentery, and cholera. Possibly, also, the germs of other diseases, such as tuberculosis and diphtheria, can exceptionally be thus conveyed, should they obtain access to drinking water.
Water may be further rendered unwholesome by moulds, ferments, and excess of decaying vegetable matter. (For water contaminated with lead, see Lead Poisoning.) Water from shallow wells and wells near drains, barnyards, cesspools, or privies is unfit for drinking.
Water containing a moderate quantity of mineral salts, 4 or 5 grains to the gallon, is not to be regarded as impure, but the composition as well as the quantity of these salts affect its power as a solvent in the tissues, and may exert a very decided influence upon the digestive system when present in the proportion of 60 or 70 grains to the gallon. The mineral waters may contain much more. Water is usually unwholesome for drinking when derived from volcanic and basaltic mountain regions, and because of organic impurities it is bad in marshy regions.
An excess of lime salts and of other mineral matters in water produces constipation, flatulence, indigestion, and favours the formation of calcareous deposits in various parts of the body. " Hard water" unites with soap and makes it less soluble, so that it is difficult to cleanse the hands with it. It also roughens the skin and dries the mucous membranes. By boiling, the hardness of water, which is due to the presence of earthy carbonates, is diminished, for the carbonic acid, which aids in holding them in suspension, is driven off. Water is also improved for drinking by filtering through a filter paper, or clean absorbent cotton on a funnel. Boiling the water does not precipitate neutral and alkaline salts, and a purgative action may still remain if they are present. Hard water is made more digestible by converting it into barley or oatmeal water. Water which contains sulphate of lime causes gastric distress and dyspepsia, and it may form calculi. " Soft water " is simply water which is free from objectionable salts. It is more wholesome than hard water. Hard and soft water have well-known characteristics in regard to their effect upon the cooking of food.
Calcareous drinking waters have been believed to be factors in the development of goitre and cretinism, notably in Switzerland, but many cases occur in which such theory is untenable.