The capacity of the pipes must be adapted to the greatest hourly demand for water. The length required is said to be about one mile to every 2,000 or 3,000 inhabitants.

The usual material for the service pipes is lead; it is therefore of much importance in initiating a water supply to first ascertain whether the water will act on lead.

(92) Water Meters.

There are two kinds of water meters, the positive and the inferential. Kennedy's and Frost's piston meters are examples of the positive kind. A piston works in a cylinder and is successively filled from the top and the bottom, and the number of strokes automatically recorded. The capacity and the piston being known the result is so many measures of water.

The inferential meter is a turbine an example of which is that known as Siemens'; the flowing water causes a turbine to revolve, and from the velocity of current as measured by the revolutions of the turbine the quantity of the water is "inferred."

(93) Constant and Intermittent Water Supply.

A constant water supply is a continual connection of the stored water supply of the company with the consumer's house, so that he is never destitute of water. An intermittent water supply is a supply only given at intervals; the water is turned off from the branch-pipes during most of the day, being only allowed to flow for a sufficient time to fill the cisterns.

A constant water supply demands special fittings, but only small cisterns or none at all. An intermittent water supply requires that each house shall have storage room for at least 24 hours supply.

Each system has its dangers, but there is less danger of local pollution in the case of constant than intermittent. In the intermittent system there is the danger of cistern pollution, besides, which, when the water at the main is turned off there must necessarily be left a vacuum in the branch-pipes and also in the mains, and foul gases may be drawn in. Two cases occurred in the writer's district, in which coal-gas was in this way sucked in in quantity and whenever the water was turned

on, a very large delivery of coal-gas preceded the burst of water. In these cases there were defects in the gas service pipe and the water service pipe, both were near together in the ground. Each time that the service pipe became empty coal-gas and air were drawn in.

With the constant service occasionally pipes will have to be repaired; in that case the water must be turned off from mains or branches, and suction will then result just the same as with the intermittent. In both cases defective mains or service pipes, although running bore full, may draw in polluting matters. It has been proved experimentally that a fluid flowing through a tube with defective joints although the tube may be bore full and at some pressure yet a vacuum may occur at the joints and any gas or liquid in contact with the joints sucked in; for instance, Mr. John Spear traced an epidemic of typhoid at Mountain Ash to the contamination of the water-main in the manner indicated.

A curious pollution of a water-main is described by Dr. Tripe in his annual report for 1887. The water from the dead end of a particular main had an offensive odour. This on investigation was proved to be caused by a large growth of weed in this portion.

(94) Fittings for Constant Water Supply.

In effecting the change from constant to intermittent the following are the rules with regard to fittings in force in the Metropolis:

(1). COMMUNICATION PIPES-Point of entry must be first approved by the company. Pipe to boundary fence should be new, or where the company allow the existing lead pipes to remain, the strength and soundness will be entirely at the risk of the consumer. Weight of pipes to be as specified in regulation. (2). Iron pipes not allowed if they are to be in contact with the ground.

Every house must have but one communication pipe.

Every house at present branched, must have its own separate "communicationpipe," except in the case of a group or block of houses or those supplied by stand pipes, the water rates of which are paid by one owner; such owner may at his option have one sufficient communication pipe for such group or block.

The connection must be made by means of sound and suitable brass screwed ferrule or stop-cock, with union, and half-inch water way.

The joints of the stop-cock and ferrule must be wiped by the consumer's plumber. All joints must be of lead and "wiped " or plumber's joints.

No pipe is to be laid in or through drains or near gas pipes.

(2). STOP-VALVE.-A sound and suitable screw-down stop-valve, not less than half an inch, and not greater than the pipe must be fixed in the communication pipe at or near the entrance, and properly covered.

(3). CISTERNS AND BALL VALVES.-All cisterns must be above ground, properly covered, accessible for inspection and cleaning, and fitted with efficient ball valves.

Wherever there is a wash-out pipe with ground plug, or any other kind of attachment, it must be connected to a warning-pipe.

(4). STAND PIPES.-Stand pipes or small cisterns properly fitted should be substituted for butt and underground cisterns.

Owners of small tenement houses are recommended, where practicable, to fix the stand pipes in the kitchens or wash houses, whereby they will be more protected from injury by frost or mischief, and future expense will be saved in repairs.

Stand pipes must not be fixed over drains.

(5) WARNING PIPES.-All waste pipes must be removed or converted into warning pipes, aud so placed that the discharge of water may be readily seen by the officers of the company. Such pipes to be of lead and of the minimum weights specified in regulation 29.1

(6). DRAW TAPS.-All draw taps must be sound and suitable, and of the screwdown kind.

Draw taps of the "screw-down" kind may be fixed on the rising main to supply water for drinking purposes.

Taps over sinks ought to be of the waste-preventer kind.

(7). STAND PIPES IN COURTS.-All stand pipes or cocks fixed outside in courts or public places to supply groups or blocks of houses, must be of the waste-preventer kind, and protected from injury by frost, theft, or mischief.

(8). WATER CLOSETS.-Water-closets, boilers, and urinals must be served through cisterns or service-boxes, each water-closet, cistern, or service-box to have an efficient waste preventing apparatus, limiting the flush or discharge to two gallons of water, and urinals to one gallon.

(9.) WATER CLOSET DOWN PIPES.-Every " down pipe" hereafter fixed for the discharge of water into the pan or basin of a water-closet is to have an internal diameter of not less than one inch and a quarter, and if of lead, is to weigh not less than 9 lbs. to every lineal yard.

(10). BATHS.-No bath to have any overflow pipe other than a warning pipe. In every bath the outlet and inlet must be distinct and unconnected, the inlet to be above the high water level, the outlet to have a water-tight plug, valve, or cock.

1 Reg. 29. All lead warning pipes and other lead pipes of which the ends are open, so that such pipes cannot remain charged with water, may be of the following minimum weights, that is to say :

CHAPTER XIII.

THE WATER SUPPLY OF THE METROPOLIS.

(95) The London Water Companies.

ALL students of sanitary science should be acquainted with the general features of the water supply of London.1

London is supplied by eight companies, and the supply is controlled in common by certain general enactments, viz. :

The Metropolis Water Acts of 1852 and 1871.

The Fire Brigade Act of 1865.

The Water Works Clauses Act of 1847.

Each company has also its special Act. The eight companies are as follows:

(96) 1. Kent Waterworks Company.

This company supply :

Deptford, Greenwich, Woolwich, Charlton, Lee, Plumstead, Eltham, Bromley, Dartford, Bexley, Erith, Chiselhurst, Mottingham, Kidbrooke, and parts of the parishes of Lewisham, Camberwell and Rotherhithe.

The water supply of the Kent Company is derived from deep chalk wells between Crayford and Deptford.

The water when viewed through a two-foot tube is of a pale blue colour; it contains less than one-tenth of a grain of organic matter per gallon, from 12 to 37 grains of common salt, from 16 to 18 grains of calcic carbonate, some salts of magnesia, potash and soda, and a small quantity of silica, the solid residue, according to Dr. Bernay's analyses, varying in different wells from 22.6 to 33.9 grains per gallon, the total hardness from 16.2° to 20.3° per gallon, and the permanent hardness from 2.8° to 7.7° per gallon.

The Company has six pumping stations and eleven covered reservoirs.

1 For further details see Colonel Sir Francis Bolton's London Water Supply, from whence the account in this book has been mainly followed.

(97) 2. The New River Company.

This company supply:

St. Martin-in-the-Fields; St. Paul, Covent Garden; St. Mary-le-Strand; St. Clement Dane; Savoy Precinct; St. John the Baptist, Savoy, Strand; St. James, Westminster; St. Anne, Soho; Rolls Liberty; St. Andrew, Holborn-above-Bars; St. George-the-Martyr; Saffron Hill; Hatton Garden; Ely Rents; Ely Place; St. Sepulchre Without; St. Giles-in-the-Fields; St. James and St. John, Clerkenwell ; St. Luke, Middlesex; St. Mary, Islington; St. Pancras; Holy Trinity, Minories; St. Katharine Precincts (Docks); The City of London; St. Mary, Whitechapel; Christchurch, Spitalfields; Norton Folgate; St. Leonard, Shoreditch; St. John, Hackney, St. Mary, Hornsey; St. Mary, Stoke Newington; Highgate Hamlet; St. Botolph, Aldgate Without; Inner and Middle Temple; Thavies, Staple, Barnard, Lincoln and Gray's Inns; Great and Little Amwell; St. Margaret ; Hoddesdon; Wormley; Broxbourne; Cheshunt; Enfield, Edmonton; Tottenham. And in conjunction with other companies, the New River Company supply:

St. Martin-in-the-Fields; St. James, Westminster; St. Pancras; St. Katharine Precinct; St. Mary, Whitechapel; Christchurch, Spitalfields; Norton Folgate; St. Leonard, Shoreditch; St. John, Hackney; St. Mary, Stoke Newington; St. John, Hampstead; Enfield; Tottenham.

The New River Company took its origin in the enterprise of Sir Hugh Myddelton who, partly at his own cost, conveyed after five years hard work water in an artificial channel from the springs in the county of Hertford into the City of London.

The New River takes its rise at Chadwell Spring, about one mile beyond Ware, in Hertfordshire. It is joined at a short distance from its source by a branch cut bringing water from the river Lee. The original length of the river was forty miles, but this has been reduced to twenty-eight miles. Along its course it also receives the water pumped up by powerful machinery from at least thirteen deep chalk wells. Besides which there are a number of service and storage reservoirs.

The company supply a population of over a million living in about 147,000 houses.

The average composition of the New River water is in grains per gallon-chlorine, 10; total oxidised nitrogen, 33; carbon, 07; hardness, 14°3; total solids, 19.9.

(98) 3. The East London Water Company supply in the County

of Middlesex:

Whitechapel, Old and New Towns; Spitalfields; Part of Bishopsgate; Artillery Ground; Part of St. Botolph, Aldgate; St. George-in-the-East; Shadwell; Limehouse; Wapping; Ratcliffe; Bow; Bromley; Poplar; Bethnal Green; Part of Shoreditch ; Hackney; Part of Tottenham in the county of Essex; East and West Ham; Low Leyton; Walthamstow; Wanstead; Woodford; Chigwell; Loughton.

The company have three distinct sources of supply from the river Lee, intake being at Chingford; from deep wells in the chalk at