2 VETERINARY HYGIENE 



matter as it may dissolve. An excessive amount of vegetable 

 matter may, however, be deleterious, and water lying on a peat 

 soil often becomes acid. Some surface waters, though quite whole- 

 some, may have a disagreeable colour, which is derived from the 

 vegetable matter. Water derived from high-lying land is called 

 Upland Surface Water and is usually pure. Surface water that has 

 been in contact with human or animal excreta may be dangerous, and 

 water from the surface of arable land should not be considered 

 fit for drinking purposes until such time as it has been purified. 



Brooks, Streams and Rivers are collections of water that 

 has run on the earth's surface, together with water that has per- 

 colated to a certain depth and has again come to the surface as 

 springs. The highest point of a river is its purest part, much of 

 the water added to it as it increases in volume is contaminated 

 surface water and is often waste water of an objectionable nature 

 from factories, &c. It must not be thought that a clear-looking 

 stream running through the country is necessarily pure and safe 

 to drink, the reverse is often the case, as it is the common custom 

 in villages for the inhabitants to discharge their soil water directly 

 into the stream. 



If a river was sufficiently long and was only polluted at or near 

 its source it would purify itself of organic impurity by the aeration 

 that takes place during its course. In this country, however, no 

 rivers are capable of self purification, and as a rule the pollution 

 increases as the river proceeds. River water contains a fairly high 

 percentage of dissolved solids which it has gathered in its course; 

 some of these may be later deposited and, as a river passes through 

 beds of different geological formation, solids of varying nature 

 may be gathered. It is well known that the character of the water 

 in a river of any length may be quite different in the various 

 sections. River water is in many instances used for the supply 

 of towns, but owing to the contamination that takes place must be 

 purified. 



Lake Water. Lakes, natural or artificial, are the common 

 sources of supply for towns. A Reservoir is an artificial lake. 

 The water forming a lake is that collected from an upland area; 

 as a rule, therefore, it is pure, but as much of the land forming 

 the catchment area is often of a peaty nature it may be acid, 

 contain a considerable amount of organic matter and be discoloured. 

 The basin of a lake is formed of rock on which the water has but 

 little solvent action, lake water is therefore remarkably free from 

 dissolved minerals and is consequently soft. The nature of the 

 rock on which the water is collected naturally affects the nature 



