One of the prime necessaries of life is an abundant supply of pure water for dietetic and cleansing purposes; after use, in the first case, it is vended by the body, and in the other, it is fouled either by personal ablution, or in the washing of houses and their contents, and in both cases it must be disposed of so as not to be a nuisance either to the occupants of the house from which it is discharged or to the community at large. Man in his primitive state disposed of the liquid refuse from his duelling by turning it on to the surrounding soil It is not necessary here to enlarge upon dangers that have from time to time arisen from the accumulated pollutions thus created ; even student of history is familiar with the devastation caused by the several outbreaks of plague in this country (and of cholera within the memory of many now living), and the inception of sanitary science as now practised may be attributed to the lessons taught by the great scourge of 1848 and 1849.1

Section VIII. - Drainage By William Spinks

Associate Member Of The Institution Of Civil Engineers;Member Of The Sanitary Institute; Lecturer On Sanitary Engineering At The Yorkshire College (Victoria University), Leeds; President Of The Institute Of Sanitary Engineers;;Author Of "Paving Private Streets","Village Drainage", "House-Drainage Manual",&C.

However pure the air surrounding a house may be, however dry the site. and however wholesome the water available for domestic purposes, that house cannot be healthy unless there is provided some system of conduits, that will convey from its precincts all the liquid refuse before decomposition has set up. This is the function of the drain, which is spoken of here in its ordinary or popular sense, and not as defined by the Public Health Act, 1875, which will be referred to at a subsequent stage. There is still one other function for the drain to perform, and that is to carry off, in addition to the liquid refuse, a certain proportion of the rain which falls on or about the house. These being the two important purposes which a drain has to serve, it is necessary to understand all the circumstances affecting each.

1 The terrible epidemic of typhoid fever at Maidstone in 1897 appears to hare been due to a water-supply polluted in this way. - ED.

The first duty is to ascertain the amount of liquid refuse likely to be discharged from a house. For making large calculations for sewage-disposal purposes, from 20 to 30 gallons per head per day is assumed or taken from the returns of the water actually consumed, but in a large town some proportion of this water does not find its way into the house-drains, as it is used for a variety of puhlic purposes (such as baths, fountains, watering streets, flushing sewers, extinction of fires, and trade purposes), and when we come to analyse the amounts consumed per house, we shall be surprised to find how great is the variation. Where people draw their water from stand-pipes, the daily consumption averages about 7 gallons per head, and in those communities where the water-supply is better but the conservancy-closet system prevails, it is about 10 gallons per head On the other hand, we may find that in large houses, where the water is conveyed to every floor, and baths, lavatories, sinks, and w.c.'s are fitted, the daily consumption may be 40 gallons on the average, and may reach as much as 70, if the occupants indulge in the daily tub. Dr. Parkes says that he found 12 gallons to be the amount used by a clean healthy man of the middle class belonging to a fairly clean household, and this amount he subdivided as follows:-

Gallona

Cooking ..

.75

Fluids as drink (water, tea, coffee,etc.)

.33

Ablution, including a daily sponge-batth taking two-and-a-half to three gallons, .

. 5.00

Share of utensil and house washing, .

. 3.00

Share of clothes (laundry) washing estimated,

. 300

12.08

Where water-closets are provided in the house, other 4 gallons at least should be allowed per head. If the closets outside are upon the slop-water system, no further amount need be calculated. The amount of faeces Parkes puts down as averaging 21/2 ounces per head per day, and of urine about 40 ounces. There may in certain houses be an addition to this liquid refuse in the shape of drainage from stables, cow-houses, and carriage washing, and in towns from slaughter-houses and from certain trades, but as the water for this purpose is usually supplied by meter, a general average quantity can be readily ascertained.

While it is very desirable to separate the rainfall from the sewage to the fullest possible extent, in order to lessen the difficulties of dealing with the sewage at the outfall-works, it is obvious that some proportion must be conveyed by the house-drain, unless it is feasible to provide two systems of conduits. In country places there is generally little difficulty in doing this, but in towns the prevalence of two systems is not an unmixed blessing; unless the methods of supervision leave nothing to be desired, from time to time connections are apt to be made of soil-drains to rain-water drains, and the presence of two systems must ultimately lead to confusion. It is in many cases, however, quite possible to separate the water falling in the fronts of houses from the sewage, and it must be remembered that in those districts where the Private Street Works Act, 1892, is adopted, councils have power to compel the owners to provide two Mirers for sewage and surface-water respectively (Sec. 9, sub-sec 1).

It may be assumed that at least the rain-water from the back portions of roofs, and that which falls on paved and flagged surfaces of yards and areas, must be provided for in the system of sewage-drains. The following table is often quoted as showing the depth of rainfall per hour flowing off various surfaces, for which provision should be made in sewers: -

Table XXIV. Flow Of Rainfall Per Hour From Various Surfaces

Inches in depth.

From roofs, .

.5

From flagged surfaces,.

.2.2

From paved surfaces,.

1

From gravel surfaces with clay subsoil,.

.05

From gravel surfaces with gravel or chalk subsoil,.

.01

From meadows or grass plots,.

.02

The average number of days per annum, upon which .5 of an inch of rain fulls in the 24 hours, is 6, and 1 inch or more falls upon one or sometimes two of those days, and very frequently that quantity is discharged in a very short space of time. On p. 128 of Symons's British Rainfall, 1884. the following extremes of rainfall in the British Isles are recorded:-