Army manual of hygiene and sanitation, 1934 / [War Office].

Date:
1941
Catalogue details

Licence: Public Domain Mark

Credit: Army manual of hygiene and sanitation, 1934 / [War Office]. Source: Wellcome Collection.

    34/310 (page 36)
    sand, etc., or animal matter from decaying carcasses or animal or human droppings. The dead impurities, like all foreign matter, if taken in drinking water, are apt to irritate the stomach and intestines causing indigestion, colic or diarrheea ; they also make it more difficult to remove living impurities from water by clogging filters or combining with chemicals and reducing their power of killing bacteria. Water containing much dead suspended matter is also muddy, unsightly and unpleasant to drink. The living suspended impurities consist of low forms of animal and vegetable life of which by far the most important are bacteria. Harmful bacteria such as those of typhoid, cholera and dysentery flourish in water which has been contaminated by the excreta of diseased men or carriers, consequently, as there is no indication from the appearance of water that it contains harmful germs, all water should be considered unsafe for drinking unless it has been treated and the germs removed or killed. In addition to germs there may be found in water certain worms which cause disease. Waters which are most likely to be contaminated with bacteria are those on or immediately below the surface of the earth, such as streams, rivers, ponds and shallow wells. The purity of water in streams and rivers varies greatly ; houses or grazing grounds near their banks or draining into them are dangerous sources of contamination, and towns or villages situated on the banks pollute the water for many miles down stream. There is less likelihood of pollution near the source of a stream, where the country is sparsely populated, or where the flow of water is rapid, as in mountainous districts. Shallow wells are always liable to pollution by sewage which has soaked into the soil from neighbouring dwellings, and all surface waters must be considered to be contaminated and unsafe for drinking until they have been treated and the germs destroyed. Water from the centre of large lakes or from midstream in big rivers is more likely to be pure as suspended matter will have had time to sink to the bottom. Water from deep wells may contain salts in solution but is usually free of suspended matter, as it has been filtered during its passage through the earth. Such water is therefore usually pure. Springs supply safe water if there are no dwellings nearby from which sewage soaks into the soil, and if the spring is ' properly protected from surface pollution. Rain water freshly collected in clean receptacles is satis- factory as an emergency supply.