Waier Supply of Belfast. 59 



decided to follow the course adopted by other towns, such as 

 Bradford, Liverpool, and Edinburgh, and to filter the town 

 water. The necessary powers were obtained from Parliament, 

 and the works are now under construction. 



But before I proceed with a formal description of the filtra- 

 tion works, I must offer a few observations respecting the 

 object of the process of filtration. Now, as is generally known, 

 we do not get water absolutely pure in nature. Even in rain 

 water there are found ammonia and particles of dust, earthy or 

 organic as the case may be, which the rain, as it were, washes 

 out of the atmosphere. Hence, where the expression pure water 

 is employed, it must be understood in a limited sense — viz., 

 water so free from objectionable constituents as to be safe and 

 wholesome for potable purposes. Thus we find in many waters 

 a considerable amount of total solid matters to the gallon, and 

 yet the water may be quite suitable for drinking purposes. 

 Within certain limits solid matters per se are not necessarily 

 injurious, and the character of the solids must be looked to 

 before an opinion can be formed. Thus, the presence of say 

 ten grains of carbonate of lime per gallon in a drinking water 

 would not condemn it, but two grains of organic matter to the 

 gallon would show the sample to be quite unsuitable for all 

 potable purposes. Impurity in water may exist in the form of 

 mineral or organic bodies or gases, and the question is how 

 these are to be removed, or so far reduced in amount, as to 

 render the water desirable for domestic use. Take the case, 

 then, of a water drawn from a river which drains a large tract 

 of country like the River Lea at Cork or the Thames above 

 London. In the latter case something like five millions of 

 people draw their supply from the river. In fine weather the 

 water is clear and well tasted, but in broken and rainy weather 

 the rivers receive a large addition in the way of earthy matters, 

 decayed vegetable bodies, and, what is the worst of all, a large 

 amount of organic matter of an animal character. To a smaller 

 extent the same applies to waters collected into reservoirs from 

 catchments of a mixed character. In flood time the water 



