Human Water Consumption Facts
It has been computed that the ancient Romans must have used over three hundred gallons of water per head per day, owing chiefly to their elaborate public baths.
In these days, however, from thirty-five to fifty gallons per head is usually considered sufficient in towns, and from twenty to twenty-five in rural districts. It is to be hoped, however, that the question of supply will be looked upon in a more generous light in the future, as the health of a community must depend to a large extent upon its water supply.
Impurities. Water nearly always contains foreign matter in suspension and solution, absorbed gases, microbes and other living organisms, but for dietetic purposes water should not contain more than a certain percentage of these impurities. Matters in suspension may be removed by filtration and settlement, those in solution by distillation, aeration, precipitation and by the aid of nitrifying organisms. Absorbed gases may be expelled by boiling and distillation, and living organisms may be reduced by filtration and settlement.
Distillation. This is effected by evaporating the water and condensing the steam. Distilled water is unpalatable, but becomes less unpleasant on aeration, which may be accomplished by exposing it to the air in thin streams and allowing it to drip over a series of trays.
Boiling. This removes temporary hardness and destroys microbes, but drinking water treated in this way also requires aeration afterwards, otherwise it is unpleasantly flat to the taste.
Nitrification. By this process, owing to the action of microbes, nitrogenous organic matter is oxidized with a formation of nitrates.
Filtration. This gets rid of suspended matter and oxidizes organic substances. Dr. Percy Frankland has shown that over ninety-five per cent of microbes were removed from Thames water by sand filtration. Sand filters are mostly used by the larger water companies, and an example is shown in picture 48, in which C represents a bed of clean sharp sand about three feet six inches thick, D another layer of sand somewhat coarser than C and about four inches thick, E another layer of sand still coarser than D and about three inches deep. F is a bed of gravel about six inches deep, and G is a course of bricks laid with open joints to allow the water to pass through to the trough H, which conveys it to the storage reservoir. Magnetic carbide of iron covered with a layer of sand has also been successfully used for filters, but to be effective this must be used on the intermittent principle to allow of aeration.
Household Filters. Until quite recently filters were almost solely designed for the purpose of removing suspended matters, to lessen hardness and to reduce the danger from organic matter. Owing, however, to the fact that ordinary charcoal filters are seldom cleaned because of the troublesome nature of the process, they usually do more harm than good. In fact, it is scarcely too much to say that the old-fashioned filter was often a disseminator of disease. The removal of micro-organisms has been the objective of the more recent types of filters, and it was mainly because the old filters were recognized as being merely breeding-places for germs that investigations were instituted.
Picture 48. Section of Sand Filter.
The Berlin Inquiry of 1886 gave great prominence to the filtration of water for domestic purposes, and that made for the German War Office in 1895 by Dr. Plagge drew particular attention to the Pasteur Chamberland and Berkefeld filters.
The Pasteur Chamberland filter is made of a porous porcelain tube through which the water is forced under pressure. The residue left on the outside of the tubes can easily be removed, and the tubes themselves should be sterilized periodically by boiling.
At Darjeeling 9500 of these tubes are in use in the municipal water-works, and the supply given is 150,000 gallons a day.
The Berkefeld filter is made upon similar lines, and a section is given in picture 49. The water supply is connected by the tap A and flows into the outer covering of enamelled iron through the hollow cylinder B, from the interior of which it is delivered to the outlet pipe C. By means of the thumbscrews DD the cylinder of kieselguhr may be removed for cleansing or sterilizing by boiling.
These types of porcelain cylinder filters are, no doubt, efficient if the cylinders are kept thoroughly clean. They are known as pressure filters, as their action is due to the force of the water from the main.
Picture 49. Berkefield Filter.
A patent automatic self-cleansing filter has been recently introduced, and is said to produce satisfactory results. pictures 50 and 51 show the construction in which by opening tap B and shutting tap A the filtered water is obtained. By shutting B and opening A ordinary unfiltered water is obtained for household purposes, and the filter is cleansed thereby automatically.
Picture 50. Elevation. Picture 51. Section.
Automatic Self-cleansing Filter.
All water for drinking purposes should be drawn direct from the main supply pipe and not from any storage cistern.
Next: Drinking Water Testing.