METHODS OF COLLECTING WATER SAMPLES

METHODS OF COLLECTING WATER SAMPLES

In order that a water supply may be examined fairly, it is of primary importance that a true sample be submitted to the analyst for examination. Anything which might result in the introduction of foreign material, especially bacteria, may easily result in improper findings which would usually be to the disadvantage of the supply. The first requisite for the collection of the sample is a properly prepared bottle. It must be chemically clean, and if there is a bacteriological examination to be made, it must be sterile. Any cleaning solution used should be thoroughly removed, since many such solutions are germicidal in character. The sterilization of the bottle should be accomplished by boiling in water, steaming or by the use of dry heat. To attempt to sterilize a bottle by means of chemical disinfectants may lead to erroneous results unless the greatest care is taken to rinse out the last traces of the chemical. Even then the repeated rinsings may defeat the sterilization by introducing contaminating material. The bottle should be closed with a glass stopper because cork stoppers arc difficult to sterilize by the means usually at hand outside of the laboratory and have the additional disadvantage of yielding various substances to the water from the many cracks and crevices. The use of corncobs, rolled paper and such substances is naturally to be avoided. Jugs should never be used because the roughness of their interiors is likely to cause adhering materials to be much more difficult to remove. It is also impossible to see whether or not the jug is clean. It is best in all cases to send to the examining laboratory for the collecting bottles because any such laboratory will be found equipped with suitablt apparatus for the cleaning and sterilization of the sample bottles. The laboratory should provide some means of sealing sterile glassware and you should receive it with the seals intact, thus assuring you that the bottles are in condition for use. The collection of the water must be carefully made. It is usually a waste of time and money to entrust the collection of samples of water to an uninstructed workman. The collector should be familiar with the visual precautions to be observed in taking a sample of water since everyone does not appreciate the ease with which bacteria may be introduced or a measurable quantity of foreign matter added. When chemical tests are made to one part in a hundred or a thousand million in routine examination and bacteria are counted, the ubiquity of bacterial and the great influence of an almost imperceptible amount of dirt must be taken into consideration. The usual precautions are as follows: 1. Allow the water to flow until the water which has stood in the pipe has wasted because since it has stood in a more or less warm place for some time, the bacteria have probably increased in number and chemical changes have gone on. If the sample is taken from a street hydrant or similar source an accumulation of iron will need to be flushed out. 2. Remove the cover from the top of the bottle, holding it in such a way that the inside of it is not soiled by contact with the hand or any other object. Open the bottle while the water is running; fill it nearly full, rinse, refill; rinse the ground part of the stopper and insert the stopner. Take great care throughout that the stopper, the inside of the neck of the bottle and the water collected are kept from contact with the outside of the faucet, the hand, a cloth or any other object. 3. Protect the top of the bottle from dust and other contaminating substances by replacing its cover of tin-foil or cloth. When a sample of water has been properly collected in a proper sort of container, the manner of shipment to the laboratory must be considered. Chemical and bacterial changes take place with ranging rapidity depending on the character of the water, the temperature at which it is kept, the exposure to light, etc. To secure the best results—that is, to deliver it to the laboratory in as nearly unchanged condition as possible, the time consumed in transit should be short and the temperature of the water should be kept low. The low temperature retards the multiplication of bacteria and minimizes the chemical changes. For some time the water laboratory here has been using one-gallon glass-stoppered bottles for the collection of water samples. The bottle is slipped into a felt lined case, open at the top. It fits tightly into the case and the felt lining serves to protect the bottle from breakage and to protect its contents to a certain extent from extremes of temperature. The case is left open at the top so that the express men can see what they arc handling and use suitable caution. Concerning the breakage of bottles in shipment it is only fair to state that our breakage has been less than 1 per cent. The bottle is prepared for use by cleaning with a strong solution of potassium bichromate and sulphuric acid as directed in the Standard Methods of Water Analysis and then sterilized by steam. A sterilized muslin cloth is tied over the top by a stout cord, the ends of which are then sealed upon the top of the stopper by an official wax seal. The gallon-bottle outfit was adopted when the laboratory was first established because the investigations of Whipple and others (as well as some work in our own laboratory) had shown that chemical and bacterial changes are less in a large bottle of water than in a small bottle of the same water, given the same temperature conditions. A long series of experiments carried out during the summer months has shown us that, while we are able to get bacteriological results of considerable diagnostic value from samples, so collected, the bacterial counts are not rigidly exact enough to be of great value in checking up the operation of a water works filter plant. For this purpose, we have used a smaller bottle packed in a case which may be iced. Penniman and Enslow of the Maryland State Board of Health have recently reported on their successful use of a one-pint sample for chemical analysis. This container was not intended to furnish a bacteriological sample as well. Since only a few more c. c. are required for the ordinary bact. counts and fermentation tubes, it occurred to us that we might use a similar sized bottle and send the sample packed in ice in a case slightly smaller than the old bacteriological case which we had been using. The ice packing should serve to retard chemical and bacterial changes even more than the use of such a container as our old one. Under such conditions it is necessary to collect only a small extra quantity of water to allow for accidents, and for rinsing of the measuring vessels. The new case is in the form of a box about 8 1/2 x 8 1/2 x 11 inches furnished with hinged cover, hasp and handle. The inside dimensions are 7 x 7 x 9 x 1/2 inches. It is lined with galvanized iron. A lead seal securing the hasp of the box insures the sterility of the bottle. It requires about six pounds of ice to fill the container properly. A few ounces of excelsior or saw dust should be added with the ice. Most of our samples reach us within 48 hours after collection.

Senior Water Bacteriologist and Chemist, Laboratories for the State Board of Health, State University of Iowa, Iowa Citv. Abstract of paper read at meeting of Iow Section of American Water Works Association, Iowa City, Ia., December, 1915.

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