I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Vol. 21, No. 2
Factors Contributing to Quality of Public Water Supplies' H. E. Jordan INDIANAPOLIS WATRRCOMPANY, INDIANAPOLIS, IND.
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HERE are five important divisions under the general heading of municipal sanitation-water supply, recreational facilities, refuse collection and disposal, sewage collection and disposal, and air condition. It may seem peculiar to include recreational facilities under the heading of municipal sanitation, but a thorough-going analysis of the effect of the adequacy or lack of such facilities upon the growing child, and adult as well, will indicate that it is a very material factor in community mental and physical health. Public water supply and the relative value of the different elements that contribute toward quality of water are considered here. I n a tentative and unpublished rating table prepared for the Illinois Public Service Commission several years ago, one of their engineers suggested that, on the basis of 100 possible points that public water supply might be given, up to 30 could be allotted to quality, up to 24 to continuity of service and pressure, 11to adequacy of fire pressure, 8 to adequacy of reserve capacity, and the balance of 100 per cent to a number of small items relating to the efficiency of the organization and the good will that such efficiency would produce. Under the heading of quality, to which this engineer assigned a total possible value of 30 per cent of the total rating of the utility, we may consider five items-safety, taste, chemical balance, appearance, and temperature. Uses of Public W a t e r Supplies
Before entering into a discussion of the importance of these factors, it is worth while to visualize the uses to which a public water supply may be put. A recent analysis by Mabee2 of the Indianapolis Water Company shows in 123 of the larger cities of the country an average per capita demand of 98.67 gallons (373.50 liters), of which 24.72 per cent was not accounted for in the metered or estimated sales to various classes of users. Extending these figures on the community basis, we then have an average of a little less than a 10,000,000gallon (37,854,300 liters) daily demand per 100,000 population, of which approximately 2,500,000 gallons (9,463,575 liters) will not be accounted for in sales return. From another standpoint we may develop the community demand beginning with the individual. On an average, not more than 0.5 gallon (2 liters) will be used by any person for drinking or as a part of his food intake. About 30 gallons (113 liters) additional is represented by the various household uses of water, such as cleaning, bathing, etc. This 30.5 gallons (115 liters) represents the total personal use to which a water supply is likely to be put. This is not far from an actual condition in a great many small English communities. A recent survey of congested districts in New York indicates a daily per capita of from 12 to 20 gallons (45 to 75 liters) only. Added to this personal use is a varying quantity ranging from 10 to 80 gallons (38 to 303 liters) per capita per day which will be devoted to commercial or industrial uses. If the industrial use exceeds 80 gallons (303 liters) per day, i t is likely to be localized in large unit industries which do not avail themselves of the facilities offered by the public supply, but locate their plant where a body of water, with such degree 1 2
Received August 27, 1928. J . Am. Water Works Assocn., 19, 639 (1828).
of purification as the peculiarities of the industry require, will be available. I n the typical 100,000-person community we have, then, not more than 50,000 gallons (189,272 liters) per day likely to be used for drinking and not much more than 3,000,000 gallons (11,356,300liters) per day devoted to all the domestic uses to which water may be put. But in analyzing the quality demands made upon a public water supply organization it will have to be laid down as a primary consideration that the 50,000-gallon (189,272 liters) individual demand is the controlling factor in water supply quality. The industrial demand of the community may be large and the general household uses of water may be subject to rigid requirements, but the first barrier to be passed in obtaining an acceptance of the water as delivered is its reaction, either physical or psychological, on the individuals in the community. S t a n d a r d s for Quality of Water Supplies
A number of standards of water supply quality have been set up, some fantastic and some of such a nature that within themselves they are contradictory. Reference need be made only to the standard which is now generally accepted as the measuring stick of public water supplies, namely, the socalled 1925 u. S. Treasury Standard.3 The requirements which it lays down are briefly as follows: I-As TO SOURCE AND PROTECTION (2-A) (1) The water supply shall be-(a) obtained from a source free from pollution; or ( b ) obtained from a source adequately protected by natural agencies from the effects of pollution; or (c) adequately protected by artificial treatment. (2) The water supply system, including reservoirs, pipe lines, wells, pumping equipment, purification works, distributing reservoirs, mains, and service pipes, shall be free from sanitary defects. 11-As TO BACTERIOLOGICAL QUALITY(2-B) (1) Of all the standard (10-cc.) portions examined in accordance with the procedure specified below, not more than 10 per cent shall show the presence of organisms of the B. coli group. (2) Occasionally three or more of the five equal (10-cc.) portions constituting a single standard sample may show the presence of B . coli. This shall not be allowable if it occurs in more than : (a) Five per cent of the standard sample when twenty (20) or more samples have been examined. (b) One standard sample when less than twenty (20) samples have been examined. 111-As TO PHYSICAL AND CHEMICAL CHARACTER~STICS (2-C) The water should be clear, colorless, odorless, and pleasant to the taste, and should not contain an excessive amount of soluble substances nor of any chemical employed in treatment.
I n a supplementary section of the portion devoted to physical and chemical characteristics (2-D), the maximum concentration which is suggested as allowable for various factors is as follows: Turbidity 10 p. p. m.; color 20; no odor from sulfureted hydrogen, chlorine, or algse; not more than 0.1 p.p.m. of lead, 0.2 p.p.m. of copper, 0.3 p.p. m. of iron, 5 p. p. m. of zinc; and not more than 1000 p. p. m. of total solids of which not in excess of 250 parts may be chlorides. 8
5, 24.
U. S. Public Health Service, Pub. Health Repfs. Reprint 1019, 3, 4,
February, 1929
INDUSTRIAL AND ENGINEERlNG CHEMISTRY
The first factor mentioned above in water supply quality was that of safety. The measuring stick used by the Treasury standard for safety is B. coli density. An interpretative paragraph on this factor of the committee’s report (2-E) is as follows: It is recognized that the definite terms of bacteriological quality in which this standard is expressed represent only agreement as to safety, and not as to limiting values beyond which demonstrable or even presumptive danger lies. Between the point on which the committee is in agreement as t o the assured safety of water supplies and the point at which agreement could be reached as to their dangerous quality is a wide zone. Within this zone lie many water supplies which, if considered in the light of available evidence from all angles, are believed to be as safe as other supplies which conform to all the bacteriological requirements.
The discussion prior to the adoption of this standard was thorough and widespread. Generally, public water supplies that meet these requirements can and are being produced. Some very interesting studies on the relationship of raw water pollution to the probable end quality of water have been made by Streeter of the Cincinnati U. S. Public Health Service Laboratory.‘ These are so fundamental that they must be detailed here. First, the average well-built and well-operated plant treating water from the river basins of the Middle West can produce, fairly consistently, a finished chlorinated water conforming to the Treasury standard, if the B. coli index of the raw water does not exceed 5000 per 100 cc. On the Great Lakes, the response of water to purification processes is so much less that the permissible density of coli must be reduced to 2000 per 100 cc. Without chlorination of the final effluent, the effect of ordinary purification process is such that the B. coli index of the raw water cannot exceed 60 to 100 cc. on the river waters and probably is as low as 10 per cc. on the lake waters. Prechlorination is coming into frequent use where the character of the raw water is such as to make final chlorine demand excessive. Its use in connection with final chlorination, according to Streeter, apparently lifts the initial permissible density in the raw water of 5000 to from 10,000 to 20,000 per 100 cc. Double coagulation and sedimentation, as practiced in certain Ohio plants, give a further increase in the permissible density up to 50,000 per 100 cc. The cost of these various measures, both in operating expense and plant investment as the process becomes more elaborate, makes a material increase in the community expense for a public water supply. I n view of the foregoing data and making adequate allowance for interest charges, depreciation, and obsolescence reserve, the per capita annual charge ranges from 0.65 cent for the simple operations on a water of low pollution to $2.00 for treatment of a heavily polluted water. The difference amounts annually to $135,000 per 100,000 population. Generally speaking, American public water supplies meet the safety requirement. Nothing less is permissible. While in a rating scale one may not assign all of the quality value to the element of safety, i t must be stated emphatically that this criterion of quality is one from which there can be no deviation. The experience background for plant operation is long and thorough. Requirements in the way of plant structures are well understood. If a municipality or organization engaged in furnishing a public water supply cannot meet the plant or operating requirements necessary to produce a safe water, there is no excuse for its continuing in the business. There is no desire to overemphasize this factor, although there is a tendency in that direction. It is only one of at least five quality factors, but it happens to be the one that cannot be met with nonchalance. 4
Pub. Health Repts., 43, 1498.
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The second quality factor is that of taste. This is one that enters the realm of psychology. Taste in its broad sense is a thing that pertains to every water. It does not make any difference whether we refer to the impounded water of New England, the deep well waters of the small middle western community, the Great Lakes waters, or the waters of the Far West. Each has a taste. Taste in water is simply a function of the solution power of water. If the supply comes from a reservoir in the granites of New England, i t will in all probability have a taste derived from the vegetable growths in the reservoir. As we leave New England and travel across the country, the taste in public water supplies varies just as the degree of mineralization varies, and the citizen of one district when he travels into another will say that the water “tastes,” when what he actually means is that he is missing his accustomed taste and notices a strange one. I n addition, certain variable and preventable factors affect taste in public water supplies. A few months ago Hazens stated that “we have made progress in producing water that can be drunk with pleasure, but there is still a way to go.” Ffequently, the waters of our public supplies do not taste well at the temperature prevailing during the warmer months. Some of them do not taste well a t any season of the year. This condition is the result of the inability of the purification process used to remove materials derived from earlier pollution of the supply or the result of the reaction of materials used in the purification process with wastes polluting the raw water. I n a number of streams used as the source of water for filtration plants, the pollution load in the head waters or upper reaches is such as to produce an undesirable and overloaded condition a t some place in its course. The biological activities may later go on to the extent that the water responds well to purification processes and a very safe water can be produced, but during high temperature months, or in midwinter, when the ice cover is complete, the residual gases derived from the biological changes in the stream will be of such a nature as to produce an unpleasant taste that is variously described as “woody,” “grassy,” or “moldy.” Generally, this condition can be masked by thorough cooling, and, as the normal American insists upon ice water, he may not notice peculiarities in taste. This problem is so definite a result of gross overloading of streams that it seems entirely proper t o suggest that its elimination be a part of the sewage disposal factor in municipal sanitation and not of the water supply factor, This is doubly so when we remember that another of the factors in municipal sanitation is recreational development. Every stream in the well populated part of this country is a part of our recreational resources, and if parts near the cities are so overloaded with those same cities’ sewage that they are destroyed as recreational centers (entirely apart from any possibility of the stream after recovery being used as a source of water for a filter plant) the community owes i t to itself to restore this opportunity for recreation which its stupidity is destroying. Industrial wastes, particularly those derived from byproduct coke ovens, also have a bearing upon the problem of tastes in public water supplies. These ovens may be a part of either a steel mill or a gas manufacturing public utility. The economics of that industry are such that it has not seemed profitable to some of the operators to remove certain chemical by-products from the wastes. These by-products when added to the water in a stream that is later used for purification, so far as they are phenols, will react with the chlorine that is used in the purification process to produce a very unpleasant tasting mixture in extremely high dilutions. Some of those associated with the by-product coke industry are satisfied 6
J . Am. Water Works Assocn., 19, 429 (1928).
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that the removal of these materials from the wastes is not an unprofitable procedure, but frequently the attitude is that of noncooperation in the removal of this rather serious factor adversely affecting the taste of water supplying large communities. Taste is a very important quality factor. The estimate has been made that the city of Chicago spends $12,000,000 annually for spring waters.6 If this is true it is not improper to point out that if the city used a reasonable quantity of water per capita, the $12,000,000 spent for spring water is more than enough to pay for the purification of the entire supply for the community. Unpleasant taste is the most serious quality factor in affecting the good will of the community toward its drinking water. Boards of health may point out that the supply is not safe, but as long as it tastes well it is difficult to make the average citizen believe that it is not safe, and, conversely, it is very difficult to make the citizen believe that a bad tasting water is safe. The third quality factor is “chemical balance.” Under this heading comes that characteristic which we think of in the Middle West as hardness, as if it were the only factor in quality with which the chemical constituents of the water had anything to do. More of the water used in the United States is objectionable on account of its corrosive character than on account of its hardness. Collins’ estimates that in 1920,23,000,000 people were using municipal supplies having a total hardness of less than 100 p. p. m. and 15,700.000 were using municipal supplies having a hardness of more than 100 p. p. m. Waters having a total hardness of less than 100 p. p. m. may be classed as from moderately to a very corrosive, depending upon the diminishing hardness. There are waters having a total hardness of more than 100 p. p. m. whose characteristics are such that they may become corrosive under certain conditions. So it is worth while for those of us in the Middle West, who think of the mineralization of water as being objectionable only in terms of hardness, to remind ourselves that a larger proportion of the total urban population of the United States is suffering from the unpleasant effects of corrosive water than is suffering from the unpleasant effects of hard water. As a composite of the varying characteristics of water that are considered under this general subject, the term “chemical balance” seems to be most expressive. Bayliss has pointed out that in water that has, for example, but 25 p. p. m. alkalinity the pH should not be less than 8.7. If it has less, corrosive effects will result. Correspondingly, the minimum pH requirement for noncorrosive water having an alkalinity of 100 is 7.6 and for water of 200 alkalinity, 7.3. Corrosive water has the following adverse effects: (1) In the metals that it may dissolve or suspend that have an unfavorable effect upon health; (2) in the metals that it may dissolve or suspend that render the water unsightly or unpleasant to taste; and (3) in the destruction of distribution mains and interior service lines, and the tendency to dissolve a t one point and deposit a t another. Bayliss has estimated that filtered Baltimore water, prior to the time it was treated to reduce its corrosive capacity, was dissolving daily about 500 pounds (227 kg.) of material from the distribution system, a t an estimated annual cost for replacement of the destroyed material of $100,000. It was demonstrated by him, and has since been accepted as part of purification practice in a number of communities, that eastern waters can be very satisfactorily purified if the hydrogen-ion concentration of the water after coagulation and during filtration is maintained a t the optimum point for the reactions of the coagulating material, and after the filtration is completed and before the water is distributed to the community American Czty, 38, 171 (1928). U.S. Geol. Survey, Watev Supply Paper 496, 13. 1 J. A m Water Works Assocn, 16, 598 (1926). 8
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the hydrogen-ion concentration is decreased to a non-corrosive point by either aeration or treatment with lime or by both. The general attitude of people in communities using this type of water is t o disregard ill effects of corrosion, except as they result in personal expense for replacement of destroyed material or as they relate to power plant operation, but in a discussion of this sort they are not to be disregarded as a factor in quality that is expensive if measured in terms of ultimate maintenance cost. On the other hand, as we leave the Atlantic seacoast and travel west the streams and ground waters in increasing degree have dissolved material from the area over which they travel, until the mineralization has proceeded to the point that waters may be termed hard. Increasing attention is being given, when new purification works are constructed, to the adaptation of these works for the provision of softer water. I n support of such investments, it is pointed outQ that the average family in the Middle West may use as much as 86 worth of soap a year that would not be used if the supply had been derived from a municipal softening plant. This is probably theoretically true, but the soap use habits of the individual are not altogether conditioned upon the softening value derived from the soap, and it is not altogether safe t o assume that this amount of money would actually be saved in the case of a softer water. It is also true that a very large proportion of the people in any modern community will provide themselves with a cistern or a zeolite softener and a double piping system, which involves an investment and maintenance cost of from $24 to $30 per family per year. Cistern water in the average city is decidedly unsatisfactory. Zeolite-sor‘tened water has a great many merits, and it may be suggested that the well operated household softener will go much farther than the municipal softening plant can go in providing a non-soapconsuming water for such household uses as may be required. It is worth while, in this connection, t o remember that in providing for municipal water softening it is necessary to provide for all uses to which the water may be put in the community, whereas the individual who provides himself with a modern zeolite softener should apply it only to the household use, which has been estimated not to exceed 30 gallons (113 liters) per day per capita. In spite of the financial advantages claimed for water softening, considered from a softening point alone, there are Considerations that make it a wide improvement t o the quality factor in a public water supply. It must be granted that a softened water has a superior safety quality, that as the load upon a plant increases-and it is likely t o increase over the entire country-the added requirements of purification are more adequately and satisfactorily met by the steps incidental to softening than by other things that may be used to produce the same effect, that the water has superior storage qualities, and that, owing to the care in operation under the very recent modifications in the softening process, it is likely to be more nearly in a state of chemical balance than any other type of water. These considerations, therefore, make i t generally accepted that modifications or additions t o plant structures for purification purposes should be in the direction of water softening, if the supply is to be considered a modern one in terms of quality. We have another criterion of water quality termed “appearance.” “Safe water that is not also clean loses psychologically much of its value.” The average individual will not believe anything that he is told about the safety of a water supply if it does not look like a drinking water. If he has grown up in contact with some of the impounded waters of the East, he may have been conditioned to disregard the high
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IND. ENG.CHEM.,News Edition, 2, 5 (August 20, 1924).
February, 1929
I N D USTRIAL AND ENNXEERI S G CHEMIST R Y
color which a t seasons adversely modifies such supplies, but if he has not he will not use them. On the other hand, many maters derived from subsurface sources have dissolved considerable quantities of iron or may be of such character as to dissolve iron from the distribution system. I n either case, the tendency of such waters to deposit iron a t one season, or a t one point, and distribute it in high concentration a t other seasons, renders them objectionable, and complaint will be made from the consuming public periodically when such supplies are used. The last criterion is that of temperature, one that is not altogether easy to analyze. Spring water will be used by a person in the open, the temperature of which ranges from 50” to 60” F., but in the household where the public supply is cooled, it is possible that the temperature of water used is lower than 50” F. It is a rare community that has any choice in the matter of temperature for its entire supply. There might be found one that had the ability t o choose between a cool water and one which in midsummer would require icing before it was used for drinking. If so, the temperature factor might enter into the consideration of the wisdom of investments that might be made for one or the other supply. Temperature is the least important quality criterion because the average community can make no choice. Certain requirements in water used for cooling purposes in industries and theaters make temperature an important factor to them. Studies indicate that in a city of approximately 400,000 population, if it were possible to furnish the entire community with water having a temperature as low as the deep well waters that can be produced in the same district, an addition of 1 per cent would be made to the quantity sold, but that these sales would be made in such quantities that the return on the metered sales basis would be less than the total cost of producing and distributing the supply. On the other hand, extreme temperatures in water have forced a change in sources. The steel industry requires very large quantities of water for cooling purposes. Both in the Pittsburgh and Youngstown districts, the use of the streams by the steel mills has been so intensive that summer temperatures have gone as high as 130” F. This not only has caused the industry t o build impounding reservoirs in order to conserve the flow of the streams, but, in the Youngstown district, has been a material factor in the decision of the Mahoning Valley Sanitary District to develop a supply from an entirely new source. Values of Five Divisions of Water Quality Before assigning values to the five divisions of water quality, it is desirable t o consider the emphasis to be given to the element of safety. I n the latter part of the nineteenth century, when the drift from agriculture to industry brought about the rapid growth of our cities, it was not possible to keep up with the great increase in urban improvements required. Not only was there an indisposition to tax property owners for improvements, but in many instances there was no real knowledge of what the needs were. Conspicuous among these needsminus-knowledge was municipal sanitation. Those were the days of bitters and sirups, and as the urban population density increased infection found a fertile field. Not the least among these deficient elements in sanitation was public water supply. As the years passed community death rates brought home !essons of the part that polluted public water supplies could play in the transmission of certain diseases, notably typhoid fever. From several sources we can now combine statistical data concerning this cause of death. Johnson’O has tabulated the death rates of various ‘0
J. A m . Water Works Assocn., 3, 249 (1919).
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cities beginning with the decade 1880-1889. Little useful information is older than that. During that decade 47 cities had an average rate of 58 per 100,000, the high average being 114 and the low 26. To all practical purposes this was the decade of ignorance. The work of Pasteur, Koch, and others of that group was being done during these years. The 1890-99 decade gave for 66 cities an average rate of 47 per 100,000, lower than that of the previous decade by 10, but the high average was greater, 147 and the low average was less, only 13. During this period Sedgwick and his graduates from the Idassachusetts Institute of Technology led the way in pointing out the responsibility of public water supplies for many great epidemics, and also showed how protective measures could be applied to render them safe. This was the decade of learning how. During the next ten years 74 cities included in the tabulation gave a record of 35 deaths per 100,000, the high average being 113 and the low one 12. During these years purification works mere built so rapidly that from a total of only 6.3 per cent of the urban population using filtered water in 1900, the figure rose to 28.2 per cent in 1910. It was the decade of action in the waterworks field. But some of the leaders realized that they had oversold the public on the water supply factor, and in 1908 we find Whipple” suggesting that, with the factor of polluted water supply removed, there would remain a probable annual death rate of about 20 per 100,000 due t o other causes. A few years later, we find .Johnsonlo saying, “If all the urban population of the United States were supplied with filtered water or water of equal purity, the average urban typhoid rate would be 14 per 100,000.” RIcLaughlin,12 of the U. S. Public Health Service, prophesied that ‘(there is excellent evidence t o show that if all the water borne typhoid were eliminated in northern cities, the death rate for typhoid fever would be less than 10.” As a matter of fact, the Annual Review of Typhoid by the Journal of the American Medical Association, which began in 1910, shows a crude average urban death rate of 11.1for the 1910-19 period. This figure is the result of a consecutive annual reduction [with but one year’s exception) from 20.6 in 1910 to 4.17 in 1919. The prophecies were more than realized. What happened? The proponents of chlorination of water suggest that the general spread of that practice was a material factor. Far more important probably was the general requirement of pasteurization of urban milk supplies. I n 1917 the immunization of the nation’s military force subtracted this group a t the “typhoid age” from the field of infection. The drop in the death rate has continued to an average for 32,000,000 urban population in 81 cities during 1927 of but 1.96 per 100,000. But, as an example of the reluctance with which some sanitarians approve water quality, we find WhippleI3 in 1922 saying, “The typhoid fever rates are becoming so low that they can no longer be regarded as sufficient to measure the quality of a water supply. Polluted water may cause sickness of one kind or another, which does not find record in the vital statistics of the community. Some more careful measure of the effect of water on the health of the community is urgently needed.” What his view would have been five years later we shall not know for his death intervened, but it seems far more proper for the present-day sanitarian to state that which evidence eeems amply to prove, that public water supplies conforming to the Treasury standard are not factors in ill health, either conspicuous or subtle, in American cities. We have the psychological effect of a nation mentally conditioned to the word association “typhoid-water,” k, ‘1
I* 18
“Typhoid Fever,” p. 132. U. S. Pub. Health Service, Pub. Health Rept. 28, 1686. Trans. A m . SOC.Civil Eng., 86, 481 (1923).
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spite of the fact that we have grown out, not only from that association but largely also from the “typhoid-fly” and “typhoid-milk” association into the remaining combination, as yet practically untouched from a control standpoint, the “typhoid-carrier.” Executives of health departments, if they wish to eliminate the residual typhoid, will need to engage in the social work phase of control of the activities of the recovered typhoid patient, until he is no longer a carrier. It is doubtful if tk+e energies of the health departments or the group discipline of the people a t large is great enough to achieve this result. Returning to our main thought, we can conclude that the safety factor in water quality is a demonstrated fact in most of our communities. The standard of sanitary quality is well known, the means of purification are well understood, and the results, except in some cities reluctant to emerge from their own stupidity, are effective in promoting health. Therefore, while desiring to assign true value to the safety factor, it is necessary to reserve sufficient weight for the remaining factors to obtain for them the consideration that they deserve. It thus seems proper to assign the bare majority weight, 51 per cent, to safety. It is the greatest factor, but not the only one. Next, in order, 22 per cent of the total 100 per cent rating will be assigned to taste. Not so tangible a factor as others, but one which reflects itself more than any other in the attitude of the water user toward the supply. And in these days, when the merchandizing phase of utility service is being more closely studied, the value of “state of mind” is looming larger than it did. The water department that, in order to make its supply safe, makes it repulsive to taste and stops there with the resigned feeling that nothing more can be done is not only in error as to the facts, but is creating a bad state of mind toward the supply that is dangerous when problems of financing reasonable extensions to the system are subject to review and approval by the public a t large. To the factor “chemical balance” will be assigned a value of 20 per cent. The demerit given to the corrosive tendency of water, on the one hand, or excessive hardness on the other, and the weight in the quality sum given for the correction of either one or the other, are minimized somewhat by the fact that the cost of correcting the defect is not generally accom-
Vol. 21, No. 2
panied by any more than a corresponding saving in the individual expenditures required to repair damage. But its value grows upon observation of the attitude of communities where corrosion is checked or the water is softened. Water in “chemical balance” has a better sales value and is likely t o increase the rating as to safety, taste, and appearance. Appearance must be given weight in the rating scale. If water does not look good, the verdict of safety does not mean much. But since attainment of any one of the three above factors is likely to include good appearance, a possible value of 5 will be assigned t o this factor. Temperature has a bearing on quality, but is largely uncontrollable. It is therefore assigned a value of 2, or 2 times the percentage that would be added to sales in cities having a public water supply of high summer temperature, and a source for development of some private supplies of lower temperature. Thus, taking as a fair measure of value of the quality factor in public water supply of 30 points maximum out of 100 total, and dividing the 30 points among 5 factors on a 100 per cent basis, 51 per cent of quality can be assigned to safety, 22 per cent to taste, 20 per cent to chemical balance, 5 per cent to appearance, and 2 per cent to temperature. Such an evaluation makes it plain that safe water is the first factor in quality, but only one of several, that the reaction of the individual when drinking water is a very important one, that water that is safe and tastes good, but is either corrosive or hard, is not rated high in the quality scale, and that appearance and temperature have their weight. Those engaged in the production of public water supplies will do good service to themselves and their patrons, if they consider seriously the rating that their supply would deserve on such a quality basis. They can then adjust the conceptions they may have of its total quality value, and proceed to recast their improvement program in the light of the relative values of the demerit points. At no time should one lose sight of the fact that the users of a supply needing improvement may not appreciate the needs, and it will be just as necessary to educate them to the point of willingly supporting the financial problem involved, as first to have convinced the managers of the supply as to the propriety of the investment.
Superchlorination and Subsequent Dechlorination over Carbon of Water for Municipal Supply’ Ernst Watzl WATZL-SCHWBITZER, INC.,HURON-SIXTH BUILDING, CLEVELAND. OHIO
GREAT many authorities on water purification and many practical engineers advocate superchlorination of water, with subsequent dechlorination (sulfur dioxide, ammonia, potassium permanganate, etc.). They know what risks are taken in using inadequate amounts of chlorine, which means that harmful substances (bacteria) and much organic matter as nutrient for bacteria are left in the water. The organic matter in the water also accounts for the difference usually found in bacterial counts a t the place where the water is treated and the more distant outlets (aftergrowth). In 1926 there were eighteen more or less serious epidemics in
A
I Received August 30, 1928. Presented before the Division of Water, Sewage, and Sanitation at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
Central Europe. The most severe epidemic occurred in Hanover, Germany, in September. This city takes its water supply from various sources, one of which is a battery of wells. The water is treated and disinfected by the method standard in the United States-namely, chemical treatment, mechanical filtration, and chlorination, the average addition for the period involved having been approximately 0.8 p. p. m. of chlorine. During a heavy rainfall a small creek near the battery of wells left its banks and flooded part of the wells. The content of organic substances jumped up to about six times the normal, so that the added, amount of chlorine was consumed immediately by the organic matter, leaving nothing to destroy the also enormously increased bacteria count. For only 2l/1 hours heavily contaminated water was pumped into the combined water mains. This resulted in the death
