This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Dr. Venable, in Jour. Am. Chem. Soc, says: "The increase in the use of galvanized iron, especially in the form of water-tanks and pipes, has led to a reopening of the question as to the possible injurious effects from the use of such water. It is a matter of importance, then, to us, how far our knowledge extends on this subject, and I will collect here all of the known facts, so far as I have been able to get at them.
"The so-called galvanized iron is, of course, nothing more than iron dipped in a bath of zinc, and superficially coated with it, and, to a certain extent, alloyed with it. The character of the protection afforded the iron is galvanic (hence the name), the two metals forming a galvanic couple, so that under the action of any exciting liquid the zinc, and not the iron, is attacked. That zinc dissolves in potable waters has long since been shown by the experiments of Boutigny, Schaueffele and Lan-gonne. Distilled water and rain-water dissolve it more readily than hard water. Especially is water containing carbonic acid capable of this solvent action. So much may be taken up that the water becomes opalescent and acquires a distinctly metallic taste. It seems that by the action of water, hydrate and carbonate of zinc are gradually formed, and that this action is more rapid in the presence of certain saline matters, but is weakened by calcium salts. "As to the injurious effects of such waters, authorities differ. Fons-sagrives, has investigated the question, consulting the statistics of the French navy, and the recorded experiments of others, adding, however, none of his own. The French Government had, before this, appointed a committee to make a special report on the subject, and the investigations of Roux, in 1865 and 1866, furnished evidence enough of possible injury to health, from waters stored in galvanized iron tanks, to lead to an order from the Minister of Marine prohibiting the use of such tanks on board ships of war. Boutigny attributed grave effects to the use of these zinc-containing waters, looking upon it as probably resulting in epilepsy. Fonssagrives, however, maintains that the zinc is not cumulative, and produces no bad effects unless taken in large doses. Doubt is thrown on this position, however, by the fact that his assertions as to the limited solubility of zinc in ordinary drinking-water are not sustained by experiments. Without doubt such waters have been used for considerable length of time, and no injurious effects have been noticed. This may have been due, however, to the hardness of the water, and hence the small amount of zinc dissolved. Pappenheim states in contradiction to the assertion of Fonssagrives, that zinc vessels are dangerous, and must be carefully avoided. Dr. Osborne, of Bitterne, has frequently observed injurious effects from the use of waters impregnated with zinc. Dr. Stevenson has noticed the solvent action of rain-water on galvanized iron, and states that probably its continued use would cause injury to health. He recommends as a convenient test for the presence of zinc in potable waters the addition of potassium ferrocyanide to the filtered and acidulated water. Zinc gives a faint white cloud, or a heavier precipitate when more is present. Dr. Frankland mentions a case of zinc poisoning where well-water containing much dissolved oxygen, and but little carbonic acid, was used after passing through galvanized iron pipes. Professor Heaton has recorded the analysis of spring-water in Wales, and a second analysis of the same water after passing through half a mile of galvanized iron pipe, showing that the water had taken up 6.41 grains of zinc carbonate per gallon.
"A similar instance of zinc-impregnated water has come under my own observation. The water from a spring two hundred yards distant was brought by galvanized iron pipes to a dwelling-house, and there stored in a zinc-lined tank, which was painted with white lead. The water became somewhat turbid and metallic-tasting, and its use for drinking purposes was discontinued. Analyses were made after the pipes had been in use for about one year.
"The tank contained 4.48 grains of zinc carbonate per gallon, with a trace of iron, and no lead. Water from the pipe gave 4.29 grains of zinc carbonate per gallon, and a trace of iron.
"It is evident, then, when the dangerous nature of zinc as a poison is taken into consideration, that the use of zinc-coated vessels in connection with water, or any food-liquid, should be avoided".