CHAPTER VII
WATER
WATER
GENERAL CONSIDERATIONS
Necessity for Proper Supply
History of Public Supply
Composition of Water
CHEMICAL ELEMENTS
FOREIGN INGREDIENTS
States of Aggregation
Universal Solvent
Necessity for Water in Body
Chemically Pure Water
HOW OBTAINED
TASTE OF WATER
Hard and Soft Water
PERMANENT
TEMPORARY
Elimination of Water from Body
Amount of Water Needed for All Purposes
FOR THE BODY
FOR DOMESTIC PURPOSES
FOR CITY USE
Water Waste
CAUSES FOR
USES OF METERS
SOURCES OF WATER SUPPLY
Rain Water
SUPPLY NOT RELIABLE
EASILY POLLUTED
FILTERING NECESSARY
DESIRABLE FOR LAUNDRY PURPOSES
Surface Water
STREAMS
LAKES
IMPOUNDING RESERVOIRS
SOURCES OF IMPURITIES IN SURFACE SUPPLY
Ground or Subsoil Water
WELL WATER
SPRING WATER
TEMPERATURE IN WELLS
SHALLOW AND DEEP WELLS
CONSTRUCTION OF WELLS
SOIL AS A FILTER
METHODS OF PURIFICATION
Natural Methods of Water Purification
BY FREEZING
SELF-PURIFICATION
WATER VEGETATION
DILUTION
STORAGE AND SEDIMENTATION
SUNLIGHT
Artificial Methods of Water Purification
DISTILLATION
BOILING
FILTRATION
CHEMICAL PURIFICATION
Swimming Pools
SANITATION OF
SWIMMERS INSTRUCTED IN POOL SANITATION
SEWAGE AND REFUSE DISPOSAL
Methods of Sewage Disposal
DRY
WET
Sewage Purification
SCREENED
SEPTIC METHOD
Refuse Disposal
INCINERATION
CITY COLLECTORS
CHAPTER VII
WATER
GENERAL CONSIDERATIONS
Necessity for Proper Supply
One of the most important requisites in maintaining the organization of the material in the living body is a proper supply of water. It is absolutely indispensable to the expression of animal and vegetable life. Although not classed as a food it enters into the composition of food and hence becomes an essential article of diet.
The greatest value has always been placed upon a sufficient supply of pure water. The history of the race shows that the earliest settlements were made with a view to obtaining a supply of water; they were either on waterways or in places where water was easily obtainable from springs or shallow wells.
Water is needed not only as an article of diet, but it is also required for sanitary purposes: for cleansing the body externally, for washing clothes, and also for sprinkling streets and for other purposes such as sewage disposal in the thickly populated centers. Even in ancient times great sums of money were expended for the public supply of water.
History of Public Water Supply
A bit of history on this subject might be of interest to some. It is asserted by historians that there are aqueducts in China dating back to prehistoric times. Channels cut in solid rock have been revealed in Jerusalem in recent excavation which indicate that they were used for conveying the water supply from the country near Bethlehem and Hebron. There have been found in these excavations channels of earthen pipes cemented together and covered with rough rocks. The fact is also quite well established that water was brought to Athens from Mount Hymettos and Mount Pentelikon.
As early as 312 B. C. water was carried to Rome through an aqueduct ten miles long. It is estimated that the cost of construction of this aqueduct was about $12,700,000. Another was begun in 272 B. C., the length of which was forty-five miles. The water carried by this aqueduct was not used for drinking but for irrigating purposes and for flushing drains.
Altogether there were at least nine aqueducts that supplied the ancient city of Rome. Of these nine, three are still used to supply modern Rome. One of these was finished by Agrippa in 27 B. C.
We see by the foregoing that from time immemorial there has been a great expenditure of energy and money in producing a proper water supply for the human family. It also reveals the fact that the ancients knew something about engineering projects which some of us are likely to consider as modern accomplishments.
Composition of Water
Water is not, as was previously supposed, an elementary substance. In 1781 it was shown by Cavendish that it consisted of two parts of hydrogen and one part of oxygen (H2O), and that it could be made synthetically by combining hydrogen and oxygen in this proportion, and that it could be separated analytically by various methods into its component parts.
By volume, water is composed of two parts of hydrogen to one part of oxygen; by weight, one part of hydrogen to eight parts of oxygen. However, pure water does not exist in Nature since water is a universal solvent and in Nature it comes in contact with so many substances; therefore, it contains many substances in solution. Chemically pure water is found only in the chemist’s flask.
Water is a liquid which is clear, colorless and odorless. To be palatable it should be cool, soft, well aerated and free from sediment and suspended impurities. One cannot judge the purity of water by any one of these qualities, for water that is palatable and gives no offense upon drinking might be polluted with that which would be detrimental to health. The palatability of water may be due to the carbonic acid present, which results from the decomposition of products contained in it.
The carbon dioxide, which is present in rain water, is obtained from the air through which the rain passes. Carbon dioxide is also taken up by the water as it percolates through ground covered with vegetation. The presence of this gas increases the solvent powers of the water. Water may also contain metal in solution such as iron, arsenic and copper.
The important foreign ingredients in water are those of organic origin, such as microscopic plants, vegetable fungi, detritus of vegetable life, minute insects, infusoria, ova of insects, minute parasites, and animal debris. Water usually contains millions of various micro-organisms, mostly harmless, although at times it may also contain so-called pathogenic germs.
States of Aggregation
Water is formed into the solid state, ice, at zero degrees centigrade. At 100° C. water boils and is converted into gas or vapor, although water is contained in the air in the gaseous form at ordinary temperatures. Between these two limits, 0° C. and 100° C. water obtains in the liquid form which is its most common state. Water is the most widely distributed of all the substances. It is practically incompressible. When heated it contracts until it reaches 4° C, or 39.2° F., and is at this point taken as the basis for specific gravity of liquids and solids.
Universal Solvent
Water is the most universal solvent known in Nature. Practically all substances yield to it. Most of the water taken into the body passes through unchanged, although it is only reasonable to suppose that some of it is broken up into its elements and united with other compounds of the body.
Necessity for Water in Body
Water composes about 70% of the entire weight of the body (about 58.5% per volume). A very great amount of water is required by the tissue for the performance of the bodily functions. As the gears of machinery must be bathed in oil to prevent undue wear, so must the tissue cells be bathed in water (secretions) that there be no undue wear. The tissue cells are spoken of as being aquatic in their habits.
Rosenau in summarizing the use of water in the body says: “It enters into the chemical composition of the tissues; it forms the chief ingredient of all the fluids of the body and maintains their proper degree of dilution, and thus favors metabolism; by moistening various surfaces of the body, such as mucous and serous membranes, it prevents friction; it furnishes in the blood and lymph a fluid medium by which food may be taken to remote parts of the body and the waste material removed, thus promoting rapid tissue changes; it serves as a distributor of bodily heat; it regulates the body temperature by the physical process of absorption and evaporation.”
Chemically Pure Water
Chemically pure water can be obtained only by distillation; it is undesirable, however, for drinking purposes because of its insipidity. Before such water is agreeable for drinking it must be aerated; this may be accomplished by agitation or by passing it through a porous substance containing air. One of Nature’s methods of aerating water is found in mountain streams where the water flows down over rocks. The same thing is accomplished by fountains and waterfalls. It is the mineral matter and the gases held in solution that give water its taste, and it is the difference in these minerals and gases that causes the individual to dislike the taste of water which he is not accustomed to drinking. But this is purely a matter of taste and has no value from a hygienic standpoint, for the most impure water, water that contains so-called pathogenic germs, may taste very good.
Turbid or muddy water is not necessarily impure from a hygienic standpoint when found in rivers, but when subsoil water becomes turbid it should be regarded with suspicion.
Hard and Soft Water
The question of hard and soft water is one that must of necessity receive some consideration, but it is of more importance from an economic standpoint than from a sanitary standpoint. Soft water is generally considered to be more desirable for drinking purposes, and it is certainly more desirable for cooking. From an economical standpoint, soft water is more preferable as the hard water requires more soap to produce a lather.
Hardness of water is spoken of as being temporary or permanent. If the water remains hard after having been boiled it is known as permanently hard water. Hardness of water is due to the presence of the soluble salts of the alkaline earth metals, especially calcium and magnesium. Temporary hardness is due to calcium or magnesium carbonate held in solution as a bicarbonate by the dissolved carbon dioxide. The hardness is temporary because the carbon dioxide is driven off by boiling, and the soluble bicarbonates are precipitated as insoluble carbonates.
Permanent hardness, on the other hand, is due mainly to sulphates and chlorides of calcium or magnesium. These salts are stable and therefore are not precipitated by boiling.
Elimination of Water from Body
Water is excreted from the body through the various channels. The kidneys excrete about 50%, the lungs about 20%, the skin about 28%, while the other 2% is excreted through the feces and other minor channels.
Amount of Water Needed for All Purposes
The amount of water needed for all purposes varies just the same as the amount of water needed by the body varies with conditioning factors. The locality and the climate will enter into the consideration of the amount of water needed to meet the requirements of hygiene and sanitation.
The amount of water required by the human body in twenty-four hours varies with many factors. The age of the individual and his occupation and health, and climate would be conditioning factors. However, authorities are pretty well agreed as to the amount necessary. It is estimated that the body requires a little less than one gallon of water per day, about two quarts taken as drinking water and the balance in food.
There is a wide range of difference in the amounts estimated, for under some conditions, a minimum of seventeen gallons, or even twelve gallons, would be sufficient, while under other circumstances and in other localities as much as 300 gallons per day per individual would not be an excessive or wasteful amount. The average amount estimated per individual per day for domestic purposes is placed at seventeen gallons for all purposes. In 1918 the statistics showed that Buffalo used an average of 260 gallons per capita per day, but many cities used much less. In Berlin in 1913 the water consumption amounted to an average of twenty-four gallons per capita per day.
The hygienic importance of these figures is insignificant since they are only approximate. There are a number of factors that are not taken into consideration. The figures are estimated on the number of gallons of water pumped and no account whatsoever is taken of the water waste through precipitation and loss through leaky pipes. Some engineers maintain that fully half the water pumped is lost in these various ways. Another thing that must be considered when comparing the amount of water used by different cities is the industries. Some industries require much more water than others, therefore, if a just comparison is to be made between cities only the water that is actually passed through the private meters must be considered.
Water Waste
Consideration of the subject of water would not be complete without some reference to the amount of water that is wasted. It seems a small matter to waste water. We sometimes say there is plenty in the river. But the proposition of preparing the water for use and getting it to the individual for consumption may involve many phases of hygiene from several different angles and one of these angles may be industrial hygiene. To get water into the home and factory requires a great many processes such as laying and maintaining water mains, purifying the water and pumping. This involves several industries and trades, so the problem of a water supply is far reaching and is of vital importance to the community.
There should never be a sacrifice on the part of hygiene and cleanliness for the purpose of saving water. A sufficient amount of water should at all times be insisted upon, but certainly there should be a strenuous effort to eliminate undue waste.
The main causes of water waste will be found to be leakage in mains and service pipes and waste from defective fixtures in the house. All of this leakage and waste should be properly attended to because of the direct relation which it bears to hygiene and particularly to industrial hygiene.
The introduction of meters has been an important factor in reducing water waste. It is not the thought to limit the amount of water used or to deprive one of a sufficient amount, but there is nothing to be gained by an unnecessary waste. The introduction of meters in Milwaukee reduced the amount of water used per tap from 1,781 gallons per day to 644 gallons per day without putting any restrictions upon the consumers. It is an enormous task to provide a sufficient amount of pure clean water for a large city and certainly an effort should be made to avoid waste.
SOURCES OF WATER SUPPLY
Rain Water
The sources of our water supply may be classified as: Rain and snow water, surface water and ground or subsoil water.
The rain and snow water provide a supply for domestic purposes. This source cannot be relied upon in some sections of the country because of the variable amount of rain fall. Rain water is pure from the fact that it has been vaporized and then condensed the same as in distillation; but it does not remain long in this pure state since it is exposed to so many sources of pollution. This water is collected in receptacles called cisterns and tanks and used mostly for household purposes. It can readily be seen that water thus stored might become polluted from the surfaces with which it comes in contact. To prevent this special care would be necessary, and in the majority of cases the need for this precaution is not recognized.
This source of water supply is not very desirable since its quantity is variable and also because of the difficulty in storing large quantities and in providing protection so that it will not become contaminated and thereby rendered unfit for household use.
While rain water in its unpolluted state is a pure water, it is not suitable for drinking purposes until it is properly aerated. The air contains dust and other suspended impurities which will be precipitated with the rain and thus pollute the water. However, the amount of pollution is so small that it is of little sanitary importance. After the air has been cleared of these suspended impurities the rain water will be relatively pure. It will be noticed that after a rain the air seems clear and clean; this is due to the rain actually washing the air.
It is necessary to filter rain water collected from the surface of roofs because roofs collect impurities from smoke and dust. The average filter used for this purpose is usually inadequate and receives such little care that it is of slight value.
In the large cities or even in the larger towns the cisterns have been replaced with more modern and more satisfactory means of water supply. Rain water is soft and therefore is most desirable for laundry purposes and is also very desirable for cooking. It is not considered as satisfactory for drinking, however, as ground water or properly filtered surface water. It always contains gases such as nitrogen, oxygen, and carbon dioxide. The amount of solids varies. The storage of water in cisterns forms a good breeding place for a certain kind of mosquito, stegomyia calopus, which is supposed to cause yellow fever; but regardless of the supposed pathogenicity of this mosquito it is quite objectionable.
Surface Water
Surface water is derived from ponds, lakes, rivers and creeks; in fact, any water which is in contact with the atmosphere is known as surface water. Surface water forms really the most desirable and satisfactory source of public water supply.
Streams form natural sewers for the regions which they drain and ponds and lakes form convenient dumping places for the sewage carried by the streams, therefore it will readily be seen that the surface water is liable to great pollution from these sources. It therefore becomes necessary to purify it by some means before it can be used for domestic purposes.
At one time it was thought that streams purified themselves in their flow, but this is now disputed and has been proven to be erroneous and should be strenuously denied. There are many factors at work in Nature which purify water in its natural state. Before civilization brought about so many artificial and unnatural conditions it was true that, with the small amount of waste material emptied into the streams, Nature would, through her natural processes, keep the waters of the streams in a state of natural purity. But in the present day with not only the sewage of our large cities pouring into the rivers and lake, but also the waste material from factories and different industries, it becomes necessary to use some artificial methods for water purification.
Lakes, from a sanitary standpoint, form a more desirable source of public water supply than rivers. There are several reasons for this. First: there is possible a greater dilution of the impurities that reach the lake. Second: there is greater opportunity for sedimentation which is a very important process in water purification. Third: the water is softer than river water and freer from organic impurities.
The greatest problem that a city getting its water supply from a lake has to solve is how to keep its sewage from polluting its own water supply. To prevent this, it is necessary to place the intake for the water supply far out in the lake. The danger from pollution has become so great in some places, as in Chicago, that special canals have been constructed to carry the sewage into other channels rather than empty it into the lake.
The impurities from the sewage may travel a great distance into the lakes. Serious sewage pollution was found ten miles out in the lake from the mouth of the Detroit River. Pollution has been found as far as eighteen miles from the shore in some places.
So it is readily observed that, notwithstanding the fact that the lakes and ponds furnish a more desirable public water supply, yet this source is not, by any means, free from objections.
The impounding reservoir, which is an artificial reservoir for the purpose of storing up water, is another very reliable source of public water supply. These reservoirs are often built in the mountains by placing a dam across a ravine or canyon. The largest dam in the world is the New Croton across the Esopus Creek in the Catskill mountains in New York. It is 248 feet high, 185 feet thick at the bottom and eleven feet thick at the top. This impounding reservoir furnishes an addition to the water supply of New York City.
There are many advantages to the impounding reservoirs, but there are also many disadvantages. One advantage is that the area drained is comparatively small and therefore the pollution from that source is lessened; also the storage factor which is experienced in this reservoir is an advantage. In this way many of the so-called pathogenic microörganisms die before they are carried to the consumer. A disadvantage is that they are open to the atmosphere and light and this is conducive to stagnation because the water is still. This results in an increase in the growth of algæ and other microscopic organisms. The stagnation of the water results in an increase of the products of decomposition. This, together with the microörganisms and algæ, produce the foul smell and bad taste of the water.
The stagnation of impounding reservoirs and small lakes may become a vital factor from a hygienic standpoint. If the water is less than twenty feet deep it will be kept in motion by the wind and in this way will not become stagnant, but if it is more than twenty feet deep the lower portion will remain still. This prevents the water from mixing and therefore the under portion will become stagnant while the surface will not. If the water supply is taken near the surface there will not be so much danger from the stagnant water, but even then there are times of the year when there is a complete stirring up of the water. This mixing of the surface water and the bottom water takes place twice a year, in the spring and in the fall. This mixing is the result of the changing of the temperature of the surface water. During the summer the surface water becomes warm and the temperature may reach 80° F. In this way the warm water remains on top but is kept stirred up by the wind. The wind will not usually create a disturbance for more than twenty feet except in very large lakes where it may be as great as forty feet.
As winter approaches the water cools until finally the temperature of the surface water becomes the same or more nearly the same as the bottom water. Then the wind exerts a deeper influence and the surface and deep water will mix. During this process vertical currents may be produced. This mixing continues until all the water has been thoroughly mixed and until the temperature of the surface water goes below the point of maximum density which occurs at 4° C. The cold water accumulates on the surface where ice is often formed. In the spring the process is just reversed. The fall mixing of the water is much more thorough and intense than the spring mixing.
The changes brought by this mixing are obvious. The surface water contains a large amount of oxygen. The bottom water contains much less oxygen but a great quantity of decomposed products. The oxygen is carried to the bottom and there oxidizes and neutralizes some of the products of decomposition.
The sources of impurities in surface water are various. One of the most menacing sources is from the sewage which is carried from the centers of population. In the rivers it is the sewage of the towns and cities situated above. In the lakes it is usually the sewage of the city itself that is likely to pollute its own water supply. Under the present conditions it seems that it is easier to purify the water supply than to purify the sewage or provide some other method for its disposal.
Naturally the water of rivers is purest near the source. The reason for this is that the rivers form a natural drainage for the land through which they flow. The waste products from every process carried on in that territory find their way into the streams as a natural result of the law of gravity. The water will be found to contain large amounts of mineral and organic matter after passing through populated and cultivated areas. Purification of rivers is considered under Water Purification.
Ground or Subsoil Water
In the consideration of the three sources of water supply it is difficult to draw definite lines of demarcation since the rain and snow water soon becomes surface water and the surface water may percolate through the ground and become subsoil water.
Well water and spring water are classed as ground or subsoil water. From a hygienic standpoint water obtained from wells or springs forms a very reliable and satisfactory source of supply.
Especially is well or spring water desirable for private domestic use, since it is usually in a reasonable degree of purity and does not, therefore, require any artificial process for purification. The sources of water supply used for public purposes, made necessary because of the volume of water required, are not so satisfactory for a private or domestic supply because its purification would entail too great an expense to warrant the practicability on such a small scale. Therefore, the most desirable source when only a limited amount of water is required is the wells.
Wells may be used for public water supply and are in some of the smaller towns, but they are not so practicable as their supply is likely to be inconstant. In other words, there is danger of the wells going dry, and since they are put down at a great expense, this would be too great a risk to take even though the water thus obtained is satisfactory from a hygienic standpoint.
The above illustration shows the fluctuation of ground water. When the ground water is at the low mark the shallow well becomes dry; as the water rises it flows into the well. When the water has reached the high mark the intermittent spring becomes a flowing spring. The pressure of the ground water is great enough to produce flowing wells down on the level.
Not all wells, by any means, will furnish a pure water supply. There are many factors to consider from the viewpoint of the pollution of well water and these will be considered in due time. When water reaches an impervious strata it remains at that level and moves in a horizontal plane. Water may form in beds or be found in underground streams. It is only in the limestone regions that water forms in streams under the ground.
Poorly constructed well, polluted by seepage thru limestone.
The depth at which water is found beneath the surface varies. The water directly beneath the surface, or that which is derived from surface drainage and the rainfall, is, by some, styled the ground water. This is the shallow water. That which is found at a lower level is called the lower subsoil water or underground water.
The ground water does not provide a very desirable source of well water because there is danger of pollution from the surface. The degree of this impurity will depend largely upon the character of the soil. If it is sandy and thus provides a good filter medium there is little danger from pollution; but if the soil is of a limestone formation it makes a very poor filter and the shallow water is likely to be polluted from the surface drainage.
The subsoil water moves in the direction of the nearest body of water. That is, if it is near a river or lake its movement will be in the direction of this river or lake. For this reason a well near the seashore will contain fresh water.
In wells less than fifty feet deep the temperature of the water will be influenced by that of the atmosphere. It will be warmer in summer and cooler in winter. Some authors put this depth at much less than fifty feet, maintaining that the atmospheric temperature will have no influence whatsoever at such a depth. It is true, however, and the fact is undisputed, that in wells 50 feet deep or more the water is cool and the temperature remains constant. It is not influenced by the change in atmospheric temperature.
Sand and gravel deposits form the best source through which to obtain subsoil water. To supply any very great amount there must be a number of wells and these must be far enough apart so as not to draw from the same territory. Seventy-eight million gallons of subsoil water per day is provided at Brooklyn from twenty-four separate pumping stations. Memphis, Tennessee, is the largest city in the United States which gets its entire water supply from sand and gravel deposits.
Poorly constructed well, polluted by surface drainage.
Sandstone rock furnishes an excellent source for subsoil water since it makes an excellent filter. Because of the limited amount of water obtained in a sandstone formation this source is practicable only for a very limited supply.
Limestone formation is the most undesirable source of subsoil water supply from a hygienic standpoint. Limestone is not porous and therefore has no filtering qualities. If water does pass through this sort of a formation it must travel through its crevices and fissures.
It is very difficult to know where the pollution of water passing through limestone originates. As these fissures are usually very long, and as the water is in no way filtered as it passes through them, the contamination might enter the water at a point far distant from where the well is sunk. The water supply from limestone is likely to be inconstant because the water is not contained in the limestone, but flows through the cracks and crevices. In this way it may soon flow away unless the source is replenished by rain or snow.
Water from the subsoil is obtained, as has been stated, from wells. Wells are classified as shallow and deep. By a shallow well is commonly meant one that is dug and not more than thirty feet deep. This type is usually walled up with brick or stone and is from five to six feet in diameter. Shallow wells may also be driven. That is, a gaspipe with a sand point is driven into the ground until the water-table is reached, the water being pumped out with an ordinary suction pump.
Shallow wells must never be considered a satisfactory source of water supply where there are conditions existing which would result in such pollution of the ground that the water percolating through can not be more or less filtered. Sewage polluted soil never is satisfactory for shallow wells.
Showing a properly constructed well in unsanitary locations.
Deep wells are drilled and are from six to eight inches in diameter. The water from deep wells may be free from contamination but may contain a great deal of mineral in solution and different salts which render it permanently or temporarily hard. This decreases its value from a sanitary viewpoint and more particularly from an economic standpoint.
Special attention should be given the construction of the well. The casing or walls should be as tight as possible. Special care should be exercised against the possibility of surface water percolating through the casing as this drainage will bring impurities.
The casing should project far enough above the surface of the ground to insure against water running from the surface. It should extend at least eighteen inches above the ground. The well should have a tight covering.
The ground possesses great filtering qualities and therefore great quantities of impurities will be taken from the water as it filters through. The danger is when the ground becomes so filled with impurities that its filtering qualities have been destroyed or when there is not sufficient distance between the source of pollution and the water level; also when the soil is of a limestone formation and the water, instead of percolating through it, passes through cracks and crevices, in which event it will in no sense be filtered.
It was at one time considered that wells should be ventilated and a great deal of stress was laid upon it. When it is taken into consideration that the water under ground is in no way ventilated except through the natural means, it will readily be understood that it is not necessary to provide ventilation merely because the water has been tapped by a well.
If the origin of pollution, such as cesspools, is too near the well or the well is too shallow, not allowing enough distance for purification, there will be great danger from such sources. The greatest danger is in the shallow wells. However, these are entirely satisfactory as a source of domestic supply, providing the soil is of a sandy or gravel formation and there are no barnyard or cesspools, for example, too near the wells. A shallow well in a limestone region is not satisfactory and should be discarded when at all possible. If it is necessary to use such, every precaution possible should be taken to eliminate the possibility of contamination.
METHODS OF PURIFICATION
Natural Methods of Water Purification
In considering the subject of water purification it is not our thought to go into detail and explain the processes that are necessary to accomplish a pure water supply, but to deal with the subject in a general way that we may appreciate what is necessary in this line.
We will first take note of the methods used by Nature in purifying water. Nature’s method of obtaining chemically pure water is by evaporation and condensation. The result of this method is the snow and rain water. About three-fourths of the earth’s surface is covered with water. The sun acts as a great furnace and the atmosphere as a vast still. In this way we see that a great quantity of water is distilled and returned to the earth in a state of purity. It is estimated by Summerville that “186,240 cubic miles of water are annually raised from the surface of the globe in the form of vapor chiefly in the intertropical seas.”
It is entirely erroneous to assume that the impurities in water are eliminated by freezing. Ice may contain great quantities of impurities, even so-called pathogenic germs. It has been shown that many germs are not destroyed by freezing. It is true, however, that ice will be purer than the water from which it is taken.
There are certain processes which result in a purifying influence as water is crystallized. As ice forms it excludes suspended matter and even under certain conditions will exclude dissolved substances. It will thus be seen that even though ice may not be pure, the danger from its use is greatly reduced. It is not advisable to use water from melted ice for drinking purposes.
Manufactured ice is supposed to be free from impurities, but this is not necessarily true. If ice is produced artificially from distilled or properly filtered water it will naturally be pure, provided it does not become polluted in the process of manufacture.
At one time it was believed that river water would become pure in a flow of seven miles. This, however, could not be true since the distance of the flow is of less importance than the time required for the flow.
The greatest aid in this method of water purification comes from the impurities mixing with the volume of water as it flows. The impurities become diluted and if sufficient time elapses the bacteria and microörganisms will die a natural death.
The principal process involved in self-purification of water is the oxidation of nitrogenous organic matter which is a chemical process. In the course of time the microörganisms die as a result of the biological action. Then there is the effect of dilution, sedimentation, especially in lakes and still water, and the effect of sunlight.
Food for the bacteria is lessened as a result of the destruction of the organic matter through oxidation. The minute infusoria, amœbæ and water worms feed upon organic matter and bacteria and thus aid in the process of purification. The plants known as algæ play a very important part also in water purification. They take up the organic substances and perform other functions similar to the vegetation on the land. The purifying effects of water vegetation is very important.
One of the chief sanitary safeguards in Nature is dilution. A small amount of pollution may be quickly diluted by a volume of water until it is practically harmless. In its concentrated state, however, there might be enough poison, the strength of which would be greater than the internal resistance of the individual. This would produce toxic conditions, or it might even be great enough to produce subluxations.
Sedimentation is another of Nature’s methods that is of great value. This process has been aped by man in the coagulation produced by the use of chemicals. This action is largely mechanical. During the process of sedimentation it is only the suspended matter that settles; but it is maintained that the bacteria and microörganisms become entangled and are carried to the bottom and in this way the water is freed from more than simply the mechanical impurities. If allowed to remain in storage a sufficient time, the harmful bacteria will die a natural death. There are processes, however, that take place during the time of storage which are objectionable, but these relate more to the taste or smell of the water than to the production of harmful ingredients.
During sedimentation there is a natural settling of the suspended particles. Not only is the desired result obtained in freezing the water of solids, but as the suspended matter sinks to the bottom many of the bacteria will also be carried down. Sedimentation, however, is not a method that can be used promiscuously. It is usually employed in connection with some other method; with a slow sand filter, for example, or when mechanical filtration is used.
Sunlight is Nature’s greatest germicide. Direct sunlight destroys germ life and renders much aid in maintaining sanitary environmental conditions. It has a purifying effect upon water in this way. When the water is in motion or during times of turbidity great good is accomplished from a sanitary standpoint by the direct rays of the sun.
Artificial Methods of Water Purification
The only way to obtain chemically pure water is by distillation. However, since this method is very slow and expensive, it is not at all practicable for the purification of even a private water supply, and since a chemically pure water is not required for drinking or other domestic purposes it would be entirely unnecessary to provide it. Again, distilled water is not desirable for drinking purposes since its taste is insipid until it is aerated.
When only a small amount of water is required it may be freed of organic poisonous substances by boiling. This will not, however, render water that contains lead and other stable chemical substances injurious to health safe for domestic use.