SUPPLY OF WATER. 



bodies, which are diffused over every surface in the 

 vicinity of living beings ; hence, when collected 

 from the roofs of houses, it has a tendency to 

 rapid putrefaction. Being free from saline ingre- 

 dients, it is excellent for washing, but is not 

 pleasant to drink. 



But if we resort to a district the surface of which 

 is destitute of vegetation, and remote from the 

 pollution of towns, we may obtain surface-water 

 containing little organic impurity. 



Rivers. The water obtained from streams and 

 rivers is in part what has flowed immediately from 

 the surface, and in part the water of springs. In 

 any case, a considerable amount of contact with 

 the ground has taken place, and, in consequence, 

 saline and organic matter is liable to be dissolved 

 in a greater or less degree. The extent of the 

 impregnation, as well as the kind of material 

 dissolved, will depend on the rocks and strata of 

 the river-basin. 



River-waters, besides the qualities they derive 

 from their primitive sources, are apt to contain 

 mud, decayed leaves, the exuviae of fish, and other 

 matters in suspension, and are thus deficient in 

 the clearness and transparency so essential to the 

 satisfaction of the eye in a drinking-water. More- 

 over, the water partakes of the extremes of summer 

 and winter temperature. But the great objection 

 to water from rivers is their general pollution from 

 the manure used upon the land, sewage, and 

 manufactures, so that there are now few rivers 

 left from whose lower course a supply could be 

 taken for domestic purposes. 



The existence of springs is owing to the fact I 

 of rain-water, after being absorbed by an open I 

 stratum of rock or earth, through which it is 

 allowed to percolate, coming in contact with some 

 water-tight or impervious stratum, consisting either 

 of rock or clay, by means of which its downward 

 passage is arrested and diverted laterally, so as to 

 find an exit at the surface of the ground at a lower 

 level, either through gravelly material, or some 

 fissure in the rock. 



The slow percolation through the interstices of 

 a gravelly layer, or the crevices of rocks, is the 

 cause of the mineral impurities which distinguish 

 the water of springs. At the same time, this slow 

 action most effectually rids the water of any 

 organic impurities contracted at the surface. Air, 

 too, is largely taken in by compression along with 

 the saline matter of the rocks, and the temperature 

 of the interior is imparted to the whole mass ; 

 hence it happens that springs of moderate depth 

 represent the average temperature of a climate. 

 Very deep springs are of a higher temperature. 

 The qualities that recommend water to the eye 

 and to the palate belong in a pre-eminent degree 

 to spring-water : it is clear, sparkling, and cool, 

 and is totally free from the offensive taint so com- 

 mon in all other waters, as well as devoid of the 

 animalcules generated by organic impurity. 



QUALITY OF WATER. 



Perfectly pure water is hardly to be found ; 

 rain-water, and even artificially distilled water, 

 are only approximately so. The impurities of 

 water exist either in the form of solid particles, or 

 in a state of solution, and may be considered 

 under the heads of Mineral Matter in Suspension, 

 Mineral Matter in Solution, and Organic Matter. 



Mineral Matter in Suspension. When running 

 water passes over a loose bottom, it carries the 

 finer particles of sand and earth along with it, and 

 the quicker its flow, the larger are the particles 

 that it can keep afloat. If the water comes into 

 a condition of perfect stillness, the particles 

 in suspension gradually sink to the bottom 

 the heaviest first, and the others in succession. 

 Particles of clay are the most difficult to separate 

 from water by mere subsidence ; as they are in a 

 state of finer division than particles of lime, silica, 

 or other minerals. Besides earthy matter, com- 

 pounds of iron and lead are also in some circum- 

 stances present in a solid state, and may be got 

 rid of by filtration. 



Mineral Matter in Solution. Spring-water, 

 which is generally clear and sparkling, holding no 

 solid matter in suspension, is seldom without a 

 large amount of dissolved mineral matter, some- 

 times as much as 2 parts in loco, commonly from 

 I in looo to I in 20,000. River and surface water 

 also contains more or less dissolved minerals. 



Organic Matter. The great bulk of the solid 

 matter held in solution in ordinary waters consists 

 of salts ; that is, combinations of acids with various 

 bases (see CHEMISTRY). The saline bases are 

 chiefly soda, potash, lime, and magnesia. The 

 most material are the salts of lime and magnesia, 

 as they are the causes of what is called ' hardness ' 

 in water, which we shall speak of more particularly 

 afterwards. The most important salt of lime is the 

 bicarbonate, which is derived from chalk or lime- 

 stone. Chalk or limestone is a carbonate of lime 

 that is, a compound of lime with one equivalent of 

 carbonic acid and is almost insoluble in water ; 

 but when water containing an excess of carbonic 

 acid as is the case with spring-water especially 

 passes over limestone, it gives it a double dose 

 of carbonic acid, and converts it into bicarbonate, 

 which is soluble. The waters having bicarbonate 

 of lime for their chief impurity are familiarly spoken 

 of as the chalk- waters. 



The other salt of lime often present in water is 

 the sulphate or gypsum. The important distinc- 

 tion between the bicarbonate and the sulphate lies 

 in the fact, that the first, the bicarbonate, may be 

 in great part precipitated, or thrown down in a 

 solid form, by boiling ; whereas the second, the 

 sulphate, cannot be so precipitated. 



Apart from its hardness, it has been made a 

 question whether water containing salts of lime is 

 injurious or beneficial to the human constitution. 

 The evidence led before the Royal Commission 

 above alluded to went to prove that there is no 

 reason whatever to suppose that the hardness of 

 the Thames water, which averages about 15, 

 would be in the least degree prejudicial to health. 

 Some eminent chemists have contended that a 

 moderate quantity of carbonate of lime is not only 

 harmless, but that it is actually useful in supply- 

 ing material for the bones of men and animals. 

 Considering, however, the much larger quantities 

 of carbonate of lime taken in our solid food, such 

 an additional source of supply would seem to be 

 unnecessary. Still it remains to be shewn whether, 

 when large quantities of water are drunk, those 

 waters which contain the smallest quantities of 

 mineral ingredients may not dissolve and take 

 away more from the body than harder waters, and 

 whether there should be any cause for preference 

 on these grounds. 



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