In view of the imminent danger always possible wherever human wastes are directly discharged into streams, whether from privies or sewers, it is obvious that water so contaminated should never on any account be used as drinking water. It does not follow, because a stream so contaminated has been used for months or years without producing any evidence of disease, that the water is safe. Unless an excessive amount of organic matter is so transmitted, no evidence will be found that such pollution has existed through any outbreak of disease. But if once the discharges become affected through a person having typhoid fever, then the result of the infection is apparent immediately. If, therefore, an inspection of the stream above the point where it is proposed to take the water-supply shows the existence of privies, as shown by Fig. 36, the water should not be used for domestic supply, although a number of individuals may have been using the water for years without bad effects. It is a case in which prevention is much wiser than cure, and while economy and convenience may indicate such a polluted stream to be a desirable source of supply, a proper regard for health conditions will rule it out absolutely. CHAPTER VIII _WATER-WORKS CONSTRUCTION_ Construction methods and practices which lend themselves to the development of the water-supply for an individual house may be divided into three parts, namely:-- (1) Construction at the point of collection, whether this point be a well, spring, brook, or reservoir; (2) The pipe line leading from the collection point to the buildings; (3) Constructions involved in the house, other than the plumbing fixtures. Taking up these different points in order, we may note at the outset that it is possible to employ either very simple or very complicated construction. _Methods of collection of water._ The common method is to lay a galvanized iron pipe in a ditch as far as a spring and there to protect the end of the pipe with a sieve or a grating and to leave it exposed in the water with no efforts expended on the spring itself. In a brook with waterfalls or with good slope, it is not uncommon to project a large pipe or a wooden trough into the stream at the top of a waterfall and so carry a certain amount of the water into a tub or basins from which the small pipe leads to the house. On the shores of a lake or pond the galvanized iron pipe is laid out on the bottom of the lake with the end protected by a strainer.