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Originally appearing in Volume V28, Page 409 of the 1911 Encyclopedia Britannica.
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WATER. lower and certainly not less td efficient filter can be con- 'tit structed by making the under-drains cover the whole bottom. In fig. 21 the sand i rests on small gravel of such degree of coarseness + •~~ FINE that the whole of the grains tD .'•' i' r would be retained on a sieve -) SAND. • of }-in. mesh and rejected by a sieve of I-in. mesh in • ; the clear, supported upon a -- a .r •. FINE 3-in. thickness of bricks laid _a_` sk t `~f ()RAVEL. close together, and constimime. tuting the roof of the under-"'""'-'c• drains, which are formed by CoNCREIIE- other bricks laid on thin asphalt, upon a concrete FIG. 2r.—Section of Sand-Filter Bed. floor. In this arrangement the whole of the materials may be readily removed for cleansing. In the best filters an automatic arrangement for the measurement of the supply to each separate filter, and for the regulation of the quantity within certain limits, is adopted, and the resistance at outflow is so arranged that not more than a certain head of pressure, about 21 ft., can under any circumstances come upon the surface film, while a depth of several feet of water is maintained over the sand. It is essential that during the working of the filter the water should be so supplied that it will not disturb the surface of the sand. When a filter has been emptied, and is being re-charged, the water should be introduced from a neighbouring filter, and should pass upwards in the filter to be charged, until the surface of the sand has been covered. The unfiltered water may then be allowed to flow quietly and to fill the space above the sand to a depth of 2 or 3 ft. It would appear to be impossible with any water that requires filtration to secure that the first filtrate shall be satisfactory if filtration begins immediately after a filter is charged; and if the highest results are to be obtained, either the unfiltered water must be permitted to pass extremely slowly over the surface of the sand without 405 passing through it, or to stand upon the sand until the surface film has formed. With waters giving little or no sediment, which are often the most dangerous, some change, as by the first method, is necessary. It has been proposed, on the other hand, to allow the filter to act slowly until the surface film is formed, and to discard the first effluent. This course can scarcely fail to introduce into the sand many bacteria, which may be washed through when the full working of the filters is begun; and it should not, therefore, be adopted when the source of the supply is known to be subject to human pollution. The time for the formation of an efficient surface films varies, according to the quality of the raw water, from a few hours to a few days. Judging from the best observations that have been made on a large scale, the highest rate of efficient filtration when the surface film is in good condition is about 4 in. downwards per hour of the water contained above the sand, equivalent to about 50 gallons per day from each square foot of sand. When the surface film has once been formed, and the filter has begun its work, it should continue without interruption until the resistance of that film becomes too great to permit of the necessary quantity of water being passed. That period will vary, according to the condition of the water, from eight or ten days to four weeks. The surface film, together with half an inch to an inch of sand, is then carefully scraped off and stored for subsequent washing and use. This process may be repeated many times until the thickness of the fine sand is reduced to about i8 In., when the filter bed should be restored to its full thickness. A lately discovered effect of sand filtration is a matter of great importance in connexion with the subject of aqueducts. A brown slimy sediment, having the appearance of coffee grounds when placed in clear water, has been long observed in pipes conveying surface waters from mountain moorlands. The deposit grows on the sides of the pipes and accumulates at the bottom, and causes most serious obstruction to the flow of water. The chemists and bacteriologists do not -appear to have finally determined the true nature and origin of this growth, but it is found in the impounded waters, and passes into the pipes, where it rapidly increases. It is checked even by fine copper wire-gauze strainers, and where the water passes through sand-filter beds in the course of an aqueduct, the growth, though very great between the reservoir and the filter beds,. is almost absent between the filter beds and the town. Even the growth of the well-known nodular incrustations in iron pipes is much reduced by sand filtration. From these facts it is clear that, other things being the same, the best position for the strainers and filter beds is as close as possible to the reservoir. Some surface waters dissolve lead when bright, but cease to do so when the lead becomes tarnished. More rarely the action is continuous, and the water after being passed through lead cisterns and pipes produces lead poisoning—so called " plumbism." The liability to this appears to be entirely removed by efficient sand filtration. Sand filtration, even when working in the best possible manner, falls short of the perfection necessary to prevent the passage of bacteria which may multiply after the filter is passed. Small, however, as the micro-organisms are, they are larger than the capillary passages in some materials through which water under pressure may be caused to percolate. It is therefore natural that attempts should have been made to construct filters which, while permitting the slow percolation of water, should preclude the passage of bacteria or their spores. In the laboratory of Pasteur probably the first filter which successfully accomplished this object was produced. In this apparatus, known as the Pasteur-Chamber• land filter, the filtering medium is biscuit porcelain. It was followed by the Berkefield filter, constructed of baked infusorial earth. Both these filters arrest the organisms by purely mechanical action, and if the joints are water-tight and they receive proper attention and frequent sterilization, they both give satisfactory results on a small scale for domestic purposes. The cost, however—to say nothing of the uncertainty—where large volumes of water are concerned, much exceeds the cost of obtaining initially safe water. Moreover, if a natural water is so liable to pathogenic pollution as to demand filtration of this kind, it ought at once to be discarded for an initially pure supply; not necessarily pure in an apparent or even in a chemical sense, for water may be visibly coloured, or may contain considerable proportions both of organic and inorganic impurity, and yet be taste-less and free from pathogenic pollution. There are several materials now in use possessing remarkable power to decolourize clarify, chemically purify and oxidize water; but they are too costly for use in connexion with public water supplies unless a rate of filtration is adopted quite inconsistent with the formation of a surface film capable of arresting micro-organisms. This fact does not render them less useful when applied to the arts in which they are successfully employed. Attempts have been made, by adding certain coagulants to the water to be filtered, to increase the power of sand and other granular materials to arrest bacteria when passing through them at much higher velocities than are possible for successful filtration by means of the surface film upon sand. The effect is to produce between the sand or other grains a glutinous substance which does the work per-farmed by the mud and microbes upon the surface of the sand filter. Elsewhere centrifugal force, acting somewhat after its manner in the cream separator, has been called rn aid. Sediateatatk n tanks. The sedimentation tank forms a very important help to filtration. In the case of river waters liable to turbidity the water should always be passed through such tanks before being placed in the filters. They form, moreover, additional safeguards against organic impurity. Sedimentation tanks on a sufficient scale may effect the purification of the water to almost any desired extent. This is shown to be the case by the purity of some lake waters; but the first cost of the works and the subsequent removal of the sediment are in some cases a serious matter, and any approach to the comparatively perfect action of lakes is out of the question. By the use of such tanks, however, when 1 -- I the condition of the water demands it, and by passing the effluent water through sand filters when in good condition, the number of microbes is found to be reduced by as much as 97 or even 99%. This, when attained, is undoubtedly a most important reduction in the chance of pathogenic bacteria passing into the filtered water; but much more must be done than has hitherto in most places been done to ensure the constancy of such a condition before it can be assumed to represent the degree of safety attained. No public supply should be open to any such doubt as ought to, or may, deter people from drinking the water without previous domestic filtration or boiling. DISTRIBUTION The earliest water supplies in Great Britain were generally distributed at low pressure by wooden pipes or stone or brick conduits. For special purposes the Romans introduced cast-lead pipes, but they were regarded as luxuries, not as necessaries, and gave way to cheaper conduits made, as pump barrels had long been made, by boring out tree trunks, which are occasionally dug up in a good state of preservation. This use of tree-trunks as pipes is still common in the wooded mountain districts of Europe. Within the 19th century, however, cast iron became general in the case of large towns; but following the precedent inseparable from the use of weaker conducts, the water was still delivered under very low pressure, rarely more than sufficient to supply taps or tanks near the level of the ground, and generally for only a short period out of each twenty-four hours. On the introduction of the Waterworks Clauses Act 1847, an impetus was given to high-pressure supplies, and the same systems of distributing mains were frequently employed for the purpose; but with few exceptions the water continued to be supplied intermittently, and cisterns or tanks were necessary to store it for use during the periods of intermission. Thus it happened that pipes and joints intended for a low-pressure supply were subjected, not only to high pressure, but to the trying ordeal of suddenly varying pressures. As a rule such pipes were not renewed: the leakage was enormous, and the difficulty was met by the very inefficient method of reducing the period of supply still farther. But even in entirely new distributing systems the network is so extensive, and the number of joints so great, that the aggregate leakage is always considerable; the greatest loss being at the so-called " ferrules " connecting the mains with the house " communication " or " service " pipes, in the lead pipes, and in the household fittings. But a far greater evil than mere loss of water and inconvenience soon proved to be inseparable from intermittent supply. Imagine a hilly town with a high-pressure water supply, the water issuing at numerous points, sometimes only in exceedingly small veins, from the pipes into the sub-soil. In the ordinary course of intermittent supply or for the purpose of repairs, the water is cut off at some point in the main above the leakages; but this does not prevent the continuance of the discharge in the lower part of the town. In the upper part there is consequently a tendency to the formation of a vacuum, and some of the impure sub-soil water near the higher leakages is sucked into the mains, to be mixed with the supply when next turned on. We are indebted to the Local Government Board for having traced to such causes certain epidemics of typhoid, and there can be no manner of doubt that the evil has been very general. It is therefore of supreme importance that the pressure should be constantly maintained, and to that end, in the best-managed waterworks the supply is not now cut off even for the purpose of connecting house-service pipes, an apparatus being employed by which this is done under pressure. Constant pressure being granted, constant leakage is inevitable, and being constant it is not surprising that its total amount often exceeds the aggregate of the much greater, but shorter, draughts of water taken for various household purposes. There is therefore, even in the best cases, a wide field for the conservation and utilization of water hitherto entirely wasted. Following upon the passing of the Waterworks Clauses Act 1847, a constant supply was attempted in many towns, with the result in some cases that, owing to the enormous loss arising from the prolongation of the period of leakage froma fraction of an hour to twenty-four hours, it was impossible to maintain the supply. Accordingly, in some places large sections of the mains and service pipes were entirely renewed, and the water consumers were put to great expense in changing their fittings to new and no doubt better types, though the old fittings were only in a fraction of the cases actually causing leakage. But whether or not such stringent methods were adopted, it was found necessary to organize a system of house-to-house visitation and constantly recurring inspection. In Manchester this was combined with a most careful examination, at a depot of the Corporation, of all fittings intended to be used. Searching tests were applied to these fittings, and only those which complied in every Detection respect with the prescribed regulations were stamped of waste. and permitted to be fixed within the limits of the water supply. But this did not obviate the necessity for houseto-house inspection, and although the number of different points at which leakage occurred was still great, it was always small in relation to the number of houses which were necessarily entered by the inspector; moreover, when the best had been done that possibly could be done to suppress leakage due to domestic fittings, the leakage below ground in the mains. ferrules and service pipes still remained, and was often very great. It was clear, therefore, the- in its very nature, house-to-house visitation was both wasteful and insufficient, and it remained for Liverpool to correct the difficulty by the application, in 1873, of the " Differentiating waste water meter," which has since been extensively used for the same purpose in 'various countries. One such instrument was placed below the roadway upon each main supplying a population of generally between loco and 2000 persons. Its action is based upon the following considerations: When water is passing through a main and, supplying nothing but leakage the flow of that water is necessarily uniform, and any instrument which graphically represents that flow as a horizontal line conveys to the mind a full conception of the nature of the flow, and if by the position of that line between the bottom and the top of a diagram the quantity of water (in gallons per hour, for example) is recorded, we have a full statement, not only of the rate of flow, but of its nature. We know, in short, that the water is not being usefully employed. In the actual instrument, the paper diagram is mounted upon •a drum caused by clockwork to revolve uniformly, and is ruled with vertical hour lines, and horizontal quantity lines representing gallons per hour. Thus, while nothing but leakage occurs the uniform horizontal line is continued. If now a tap is opened in any house connected with the main, the change of flow in the main will be represented by a vertical change of position of the horizontal line, and when the tap is turned off the pencil will resume its original vertical position, but the paper will have moved like the hands of a clock over the interval during which the tap was left open, If, on the other hand, water is suddenly drawn off from a cistern supplied through a ball-cock, the flow through the ball-cock will be recorded, and will be represented by a sudden rise to a maximum, followed by a gradual decrease as the ball rises and the cistern fills; the result being a curve having its asymptote in the original horizontal line. Now, all the uses of water, of whatever kind they may be, produce some such irregular diagrams as these, which can never be confused with the uniform horizontal line of leakage, but are always super-imposed upon it. It is this leakage line that the waterworks engineer uses to ascertain the truth as to the leakage and to assist him in its suppression. In well-equipped waterworks each house service pipe is controlled by a stop-cock accessible from the footpath to the officials-of the water authority, and the process of waste detection by this method depends upon the manipulation of such stop-cocks in conjunction with the differentiating meter. As an example of one mode of applying the system, suppose that a night inspector begins work at 11.30 p.m. in a certain district of 2000 persons, the meter of which records at the time a uniform flow of 2000 gallons an hour, showing the not uncommon rate of leakage of 24 gallons per head per day. The inspector proceeds along the footpath from house to house, and outside each house he closes the stop-cock, recording. opposite the number of each house the exact time of each such operation. Having arrived at the end of the district he retraces his steps, reopens the whole of the stop-cocks, removes the meter diagram, takes it to the night complaint office, and enters in the " night inspection book " the records he has made. The next morning the diagram and the " night inspection book " are in the hands of the day inspector, who compares them. He finds, for example, from the diagram that the initial leakage of z000 gallons an hour has in the course of a 41- hours' night inspection fallen to 400 gallons an hour, and that the 'boo gallons an hour is accounted for by Intermittent supply. Constant supply. fifteen distinct drops of different amounts and at different times. Each of these drops is located by the time and place records in the book and the time records on the diagram as belonging to a particular service pipe; so that out of possibly 300 premises the bulk of the leakage has been localized in or just outside fifteen. To each of these premises he goes with the knowledge that a portion of the total leakage of 2000 gallons an hour is almost certainly there, and that it must be found, which is a very different thing from visiting three or four hundred houses, in not one of which he has any particular reason to expect to find leakage. Even when he enters a house with previous knowledge that there is leakage, its discovery may be difficult. It is often hidden, sometimes underground, and may only be brought to light by excavation. In these cases, without some such system of localization, the leakage might go on for years or for ever. There are many and obvious variations of the system. That described requires a diagram revolving once in a few hours, otherwise the time scale will be too close; but the ordinary diagram revolving once in 24 hours is often used quite effectively in night inspections by only closing those stop-cocks which are actually passing water. This method was also first introduced in Liverpool. The night inspector carries with him a stethoscope, often consisting merely of his steel turning-rod, with which he sounds the whole of the outside stop-cocks, but only closes those through which the sound of water is heard. An experienced man, or even a boy, if selected as possessing the necessary faculty (which is sometimes very strongly marked), can detect the smallest dribble when the stop-cock is so far closed as to restrict the orifice. Similar examinations by means of the stop-valves on the mains are also made, and it often happens that the residual leakage (400 gallons an hour in the last case) recorded on the diagram, but not shut off by the house stop-cocks, is mentioned by the inspector as an " outside waste," and localized as having been heard at a stop-cock and traced by sounding the pavement to a particular position under a particular street. All leakages found on private property are duly notified to the water tenant in the usual way, and subsequent examinations are made to ascertain if such notices have been attended to. If this work is properly organized, nearly the whole of the leakage so detected is suppressed within a month. A record of the constantly fluctuating so-called " night readings " in a large town is most interesting and instructive. If, for example, in the case of a hundred such districts we watch the result of leaving them alone, a gradual growth of leakage common to most of the districts, but not to all, is observed, while here and there a sudden increase occurs, often doubling or trebling the total supply to the district. Upon the original installation of the system in any town, the rate of leakage and consequent total supply to the different districts is found:to vary greatly, and in some districts it is usually many times as great per head as in others. An obvious and fruitful extension of the method is to employ the inspectors only in those districts which, for the time being, promise the most useful results. In many European cities the supply of water, even for domestic purposes, is given through ordinary water meters, and paid for, Supply by according to the meter record, much in the same manner meter, as a supply of gas or electricity. By the adoption of this method great reductions in the quantity of water used and wasted are in some cases effected, and the water tenant pays for the leakage or waste he permits to take place, as well as for the water he uses. The system, however, does not assist in the detection of the leakage which inevitably occurs between the reservoir and the consumer's meter; thus the whole of the mains, joints and ferrules connecting the service pipes with the mains, and the greater parts of the service pipes, are still exposed to leakage without any compensating return to the water authority. But the worst evil of the system, and one which must always prevent its introduction into the United Kingdom, is the circumstance that it treats water as an article of commerce, to be paid for according to the quantity taken. In the organization of the best municipal water undertakings in the United Kingdom the free use of water is encouraged, and it is only the leakage or occasional improper employment of the water that the water authority seeks, and that successfully, to suppress. The objection to the insanitary effect of the meter-payment system has, in some places, been sought to be removed by providing a fixed quantity of water, assumed to be sufficient, as the supply for a fixed minimum payment, and by using the. meter records simply for the purpose of determining what additional payment, if any, becomes due from the water tenant. Clearly, if the excesses are frequent, the limit must be too low; if infrequent, all the physical and administrative complication involved in the system is employed to very little purpose. The question of the distribution of water, rightly considered, resolves itself into a question of delivering water to the water tenant, without leakage on the way, and of securing that the fittings employed by the water tenant shall be such as to afford an ample and ready supply at all times of the day and night without leakage and without any unnecessary facilities for waste. If these conditions are complied with, it is probable that the total rate of supply will not exceed, even if it reaches, the ratenecessary in any system, not being an oppressive and insanitary system, by which the water is paid for according to the quantity used. (G. F. D.)
End of Article: WATER
WATCH (in O. Eng. wcecce, a keeping guard or watchi...

Additional information and Comments

SPECIFICATION FOR BRASS FERRULS Ferrule: A pipe fitting for connecting and service pipe to a water main A ferrule shall permit leak free service pipe installation with conventional under Pressure drilling and tapping machines. Reference Standards BS 1010 part 2 1973 :Drawn off taps and stop taps S L S 596 1982 : Bib Taps and Stop Valves B S 2872 C 2122 : Brass pressure die castings for bodies and components B S 1400 POB 1 : Brass pressure die castings for bodies and components B S 2874 C2122 : Brass rod for spindles ,glands, crutches ,washers ,nuts B S 5454 clause 6 : Rubber for washers B S 5292 : Jointing materials and components for installation Using water. B S 21: Metallic screw threads The Banjo washers and the 1 ¼” to 2” top cap washer shall be manufactured in EPDM rubber to B S 2494 .the ½” to 1”to cap washer shall be manufactured in E P D M polypropylene or nit rile rubber and shall provide the sealing between the outer body and ferrules stem. GENARA All fittings shall be to “ water works” standards and shall be of a well proven robust design and construction suitable for the particular duty for which they are required and for user topical humid conditions of Sri Lanka.. All fittings shall be obtained from reputable manufactures and be constructed according to British standards specification or equivalent. All fittings shall be tested to the appropriate test pressure at the manufactures works and shall be supported by test certificates from the manufactures and shall be clearly identified by serial or reference number where possible to the material been certified and shall include information required by the relevant reference number where possible to the material being certified and shall further include information required by the relevant reference standard or specification every item shall be legibly marks equivalent which completed with on the body. Whenever necessary the supplier shall forward specimens before delivery to the site All standard material shall suitable for use with water at temperature up to 45 deg. C All brass fittings shall comply with BS standard or equivalent and shall be capable of with standing the test pressure specified. The castings shall be closed rained, sound smooth and symmetrical and shall be carefully cleaned and dressed off. No stopping or plugging will be permitted in the case of blowholes appearing in the castings all castings shall be free of blowholes and other defects shall comply BS2872 Or equipment. All threads shall be complied with ISO metric screw threads or BS21 All fittings shall be suitable for frequent operation and for infrequent operation after long periods in the open or closed condition. All non metallic materials to be provided shall be listed in the current ‘water fittings and materials Directory” published by the Water Research center UK or approved equivalent publication as having passed full tests of effect on water quality under the equipments for the testing of non metallic materials for use in contact with potable water SPECIFICATION FOR BRASS SWIVEL FERRULES GENARAL The ferrule shall be a standard pattern Brass ferrule with Female BSP screwed outlet for PVC Pipes to BS21 parallel thread All ferrules shall be designed as a main stem with single 360º swivel outlet for PVC 90º with control of water flow via a threaded inner plug The inlet shall be a male taper thread to BS21/ISO 7/1. The ferrules shall be designed for use underground and to handle potable water to temperature of water up to 35º C and suitable to working at pressure of 15-20 bar (225-300 PSI) without leakage DESCRIPTION OF DESIGN The design of the ferrule shall permit service pipe installation via conventional drilling and tapping machines dry under reassure with or without service saddles The design of the ferrule shall further permit use with conventional drilling machines which mount on to the ferrule/saddle assembly and drill the main via the ferrule stem waterway, dry or under pressure in to the wall of CI, DI, PVC or asbestos cement pipes of various diameters CONSTRUCTION The ferrule stem. Banjo, inner plug and top cap shall be manufactured of brass to BS 2872 CZ122/ISO RS 426 The banjo washers and the 1¼” to 2” top cap washer shall be manufactured in EDPM rubber to BS 2494. The ½” to 1” top cap washer shall be manufactured in polypropylene or nit rile rubber and shall provide the sealing between the outer body and ferrules stem. A treaded brass stop plug shall prevent the ingression of dirt. SPECIFICATION FOR STOP TAP The rising type brass stop taps shall comply with BS1010 or SLS: 198 and the relevant stranded numbers shall be clearly marked or stamped on the body of all valves Material for body, body components, and washer plate and for spindle, glands crutches, washerplates, nuts etc shall be cast brass and leaded brass respectively. The materials shall have chemical composition as stipulated in table1 and 2 of SLS 596: 1982 when analyzed by the atomic absorption photometric method or any other method agreeable to the engineer. All castings shall be sound and free from laps, blowholes and fittings and both external and internal surfaces shall be clean and smooth and free from sand Every valve shall be clearly marked the direction of flow trademark or manufactures name and nominal size of the body. All the screw threads shall conform to the bask profile of ISO metric screw threads given in SLS 268. The thread dimensions of gland bonnet and spindle shall strictly accordance to the relevant standard. TEST CERTIFIATES Manufacturers test Certificate and an independent recognized testing institution is acceptable .
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