Thames, the average rainfall per annum is only about 23 inches ;
along the south coast it is about 35 inches; whilst in the
mountainous districts of Cumberland, Westmoreland, Wales,
and Devonshire, the average exceeds 75 inches. Up to about
2000 feet the amount of rainfall increases with the elevation ;
above this level, the clouds having already deposited most of
the moisture they originally contained, the amount decreases,
or at least no longer increases. Where the hills do not reach
2000 feet, and where they are cut through by valleys, more
rain is deposited on the lee side of the hills and over the country
opened out by the valleys. The following gaugings by Mr.
. Bat em an, taken along the line of the Rochdale Canal across
the Pennine Chain 2 " show to a marked degree the abstrac-
tion of moisture caused by the intervention of a range of
hills."
1 Proc. Brit. Met. Soc. 1861.
2 De Ranee — The Water Supply of England and Wales.
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RAIN AND RAIN WA TER 1 5
Annual Rainfall.
At Rochdale . 84*25 inches At foot of western slope.
White Holmes, Blackstonel __ rr tOAA f . , . _ ,
, ' f 52*55 ., 1200 foot above hoa- level,
edge .... J
Toll Bar ,, 63*16 ,, 1000 feet above sea-level.
Black House „ 5180 „ 1000 feet alx>ve sea-level.
Sowerby Bridge . . 29*85 ,, 800 feet above sea-level
at foot of eastern side of the hills.
Over some five-and-a-half millions of square miles of the land
surface of the globe rain seldom or never falls — (the deserts
of Sahara, Gobi, Kalahari, the interior of Australia, etc.)
Near the equator the rainfall is almost perpetual. At
Cberraponjee, in the Khasia Hills, in Assam, the average rain-
fall is over 400 inches. Probably the wettest district in
England is the Stye Pass, in the Cumberland Hills, where
about 200 inches falls annually, the average over the whole
of England being about 30 inches. Speaking generally, the
rainfall varies with the latitude, altitude, distance from the
sea, direction of the prevailing winds, extent of forests, and
position with reference to mountain ranges.
The rainfall also varies greatly at certain seasons. Over
nearly the entire sub-tropical region winter is the rainy
season. According to Scott l the exceptions are " the eastern
coast of the great continents, as China and the eastern
states of the Union, which enjoy a sort of monsoon rain in
the height of the summer. Natal in Africa and the Argentine
Republic come under the same category. All these countries
receive abundant rains at the period most favourable for the
growth of crops. . . . The countries with winter rains and
summer droughts must have recourse to irrigation to water
their fields." In other regions farther north, rain falls at all
periods of the year, as in the British Isles. On the west
coast most rain falls in January, but on the opposite coast
September, October, and November are the wettest months.
The mean monthly rainfall at Kew, Greenwich, and in
1 Elementary Meteorology,
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16
WATER SUPPLIES
Massachusetts for various periods is given in the subjoined
table :—
Kew.
Kew.
Greenwich.
Massachusetts. 1
1813-72.
1865-80.
1881-90.
January
1-9
2 2
1-3
37
February
1-5
17
1-3
3 a
March .
1-5
1*3
1-3
3-9
April .
17
1-85
1-3
3 3
May .
2*1
1-6
1-6
3*3
June .
2-0
2*1
1-6
3 3
July .
2 3
2*4
2-2
3-8
August
23
2-2
1-6
4*1
September
235
2*5
17
3
October
27
2 5
1*9
37
November
2 3
1*9
2
3 9
December
1-9
2-2
1-4
3-5
The variation in the rainfall in any given district in different
years and in different parts of the year has an important
bearing upon the question of water storage, and will be
considered in the section treating of that subject.
A precise knowledge of the amount of rainfall is absolutely
necessary where the total amount of water falling upon a
given area has to be ascertained, and this knowledge can only
be obtained by careful collection and registration. Such
records also, if properly kept, are of the greatest service in
enabling approximate estimates to be made of the amount of
water which can be collected, and for comparing the rainfall
over different areas. It is very desirable, therefore, that some
uniform plan of collection and registration should be adopted.
The Royal Meteorological Society gives to its observers the
following instructions (Hints to Meteorological Observers, with
Instructions for Taking Observations) : —
" Bain-gauge. — The rain-gauge should be made of copper,
and have a circular funnel of either 5 or 8 inches diameter,
with a can or bottle inside to collect the water. It is very
1 Average deduced from long-continued observations in various parts
of the State. Report on Water Supplies, 1889-90.
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RAIN AND RAIN WATER 17
desirable that it should be of the Snowdon pattern — that is,
with a 6-inch cylinder and a sharp brass rim (Fig. 1).
" It should be set in an open situation, away from trees,
walls, and buildings — at the very least as many feet from
their base as they are in height — and it should be so firmly
Fig. 1.— Snowdon Rain-gauge.
fixed that it cannot be blown over ; the top of the rim should
be one foot above the ground, and must be kept quite level.
" The measurement of the rainfall is effected by pouring
out the contents of the water of the bottle or can into the
glass measure, which must be placed quite vertical, and read-
ing off the division to which the water rises ; the reading is
to be taken midway between the two apparent surfaces of the
water. The glass measure is usually graduated to represent
tenths and hundredths of an inch, and holds 0*50 inch of rain-
fall. Each division represents the one-hundredth of an inch,
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1 8 WATER SUPPLIES
the longer divisions five-hundredths, and the long divisions,
having figures attached, tenths of an inch. If there be more
than half an inch of rain, two or more measurements must be
made, and the amounts added together. The complete amount
should always be written down before the water is thrown
away. The gauge must be daily examined at 9 a.m., and the
rainfall, if any, entered to the previous day ; if none be found,
a line or dash should be inserted in the register. It is desir-
able that very heavy rains should be measured immediately
after their occurrence, entering the particulars in the remarks,
but taking care that the amount is included in the next
ordinary registration.^
" Snow. — When snow falls, that which is collected in the
funnel is to be melted and measured as rain. This may
quickly be done by adding to the snow a measured quantity
of warm water, and afterwards deducting the quantity from
the total measurement. If the snow has drifted, or if the
funnel cannot hold all that has fallen, a section of the snow
should be obtained in several places where it has not drifted
by inverting the funnel, turning it round, lifting and melting
what is enclosed. The section should, if possible, be taken
from the surface of a flat stone."
In mountainous districts, and for waterworks purposes, in
which it is only necessary to make weekly or monthly obser-
vations, a special form of rain-gauge must be used. 1 Mr.
Symons' pattern is admirably adapted for this purpose (Fig.
2). The cylinder in which the water is collected will contain
48 inches of rain, and by aid of a graduated rod and float,
readings may be taken to one-tenth of an inch. The rod is
detached and only introduced when an observation is being
made. In districts where the annual rainfall does not exceed
40 inches, the collecting cylinder may be of smaller capacity.
If the area of the mouth of the funnel be twice that of the
cylinder, the float will rise 2 inches for each inch of rain,
and the accuracy of the readings is increased.
1 MM. Richard Fr eres of Paris make a self-registering rain-gauge.
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RAIN AND RAIN WATER 19
One inch of rainfall corresponds to nearly 4 J gallons per
square yard, or 22,620 gallons per acre. If 1 inch of rain
fell upon some impervious surface, such as a roof, covering
say 10 square yards of
ground, the amount of
water which could be
collected, providing none
were lost by evaporation
or from any other cause,
would be 46| gallons.
To obtain anything ap- 1
proaching this amount,
however, the rain would
have to be heavy and con-
tinuous. If it fell in a
series of slight showers
spread over any consider-
able interval, and especi-
ally in hot weather, only
a very small proportion
indeed would be collected
— nearly all would be lost
by evaporation. When the
rain falls upon more or less
pervious soil covered with
vegetation, it is only the
heavy rains or long-con-
tinued showery weather
which yields sufficient
water to percolate into
the subsoil to feed the
, . , , . Fig. 2.— Symons' Mountain Rain-Gauge.
springs and raise the level
of the subsoil water {vide Chapter IV.). The total rainfall
and the rainfall available for water supplies are therefore not
identical terms.
Rain water collected from a clean, impervious surface in
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20 WATER SUPPLIES
the open country is the purest of natural waters. In passing
downwards through the air, however, it not only takes up a
proportion of the gaseous constituents, but also washes the
air from all floating impurities, whatever their nature. The
rain which first falls always contains the largest proportion of
these impurities. In the neighbourhood of towns the rain
contains soot, sulphuric acid, and other matters derived from
the combustion of coal, together with ammoniacal salts,
nitrates, and albuminous matters derived from decomposing
animal and vegetable substances, and the exhalations from
the bodies of men and animals. Minute traces of these
substances, together with common salt (derived from the sea)
and various micro-organisms, are found in all rain waters.
One gallon of rain contains on an average 8 cubic inches
of gases, of which about one-third is oxygen and two-thirds
nitrogen. The carbonic acid amounts only to about two
per cent of the mixed gases.
Dr. Angus Smith, in his work on Air and Rain, states
that rain from the sea contains chiefly common salt ; that the
sulphates increase inland before large towns are reached, and
seem to be the products of decomposition, the sulphuretted
hydrogen from organic compounds being oxidised in the
atmosphere ; that the sulphates rise very high in large towns
because of the amount of sulphur in the coal used as well as
to decomposition; that when the sulphuric acid increases
more rapidly than the ammonia, the rain becomes acid ; that
free acids are not found with certainty where combustion or
manufactures are not the cause ; and that ammoniacal salts
increase in the rain as towns increase : they come partly from
coal and partly from decomposed organic substances. The
observations of Dr. Miguel at Montsouris, Paris, on the
micro-organisms found in rain, prove that bacteria, pollen,
spores of fungi, protococci, etc., constantly occur, and are
especially numerous in the warmer months ; and in the first
showers after a long spell of dry weather over 100,000 such
organisms may occur in a single pint of rain water.
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RAIN AND RAIN WATER 2\
The foregoing remarks refer only to water collected directly
in clean vessels. If the rain has fallen upon a roof it may
become seriously contaminated by the excrement of birds,
decaying vegetable matter, soot, and dust ; in fact some of
the filthiest waters used for domestic purposes which I have
examined have come from rain-water tanks. The solid
organic matters are washed from the roof or other collecting
surfaces into the tanks ; these undergo further putrefactive
change, the products formed entering into solution and accen-
tuating the pollution. When properly collected, rain water
can be stored and utilised for all domestic purposes. Since
it never contains more than a trace of lime salts in solution,
it is exceedingly soft and well adapted for washing. Its taste
is mawkish and objectionable, but this can be remedied by
filtration ; in fact it can be rendered quite palatable. Rain
water, especially in certain districts where manufacturing
towns abound, is frequently distinctly acid, and then acts
freely on various metals. It is not safe, therefore, to store it
in lead, zinc, iron, or galvanised iron tanks. Slate tanks may
be used, but if the joints are made with white or red lead,
the angles where the lead is exposed should be filled in with
cement. This not only prevents the lead being acted upon,
but renders the jointing more secure and facilitates cleansing.
Earthenware can be used for small cisterns. Large storage
tanks may be built of brick, and, if underground, should be
well puddled outside with clay. The bricks should be set
with hydraulic lime mortar and the inside of the tank lined
with Portland cement. The object of these precautions is not
only to prevent the rain water wasting by leakage, but also
to prevent ground water gaining access. Access of surface
water must also be guarded against by roofing over in a
similar manner. By proper collection and storage of the
rainfall it is often possible to obtain a fairly abundant supply
of good water for a farm, dwelling-house, or even a group of
houses. To effect this, three conditions are necessary : — (1)
The tank must be of sufficient size to store all the available
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22 WATER SUPPLIES
rainfall, and must be properly constructed. (2) The first
portion of every shower which washes the roof or other col-
lecting surface, and is therefore always filthy, must not
be allowed to enter the storage tank. (3) There must be
some efficient system of filtration. The area covered by the
average country cottage may be taken at 35 square yards,
and the available rainfall collected from a roof cannot safely
be estimated at more than half the total rainfall. Much is
lost by evaporation ; many slight showers do not yield enough
water to reach the tank, and in very heavy showers much is
often lost by the water running over the eaves troughing, or
over the ends of the cottage where there is no spouting.
Assuming the rainfall to be the average, from 15 to 18 inches
could be collected. This would yield for the year about
3200 gallons, or 9 gallons per day. It is evident that this
would not be sufficient to meet all requirements ; but even
in the worst districts there are ponds or brooks from which
water could be obtained for slopping purposes. With a
larger roof area, of course a larger amount of rain water
would be available ; but as few cottages cover an area of
40 square yards, 9 gallons would be the maximum supply.
In the eastern counties, where the rainfall is only from
20 to 25 inches, even this amount cannot be obtained, but
in districts where the rainfall exceeds the average more could
be collected. The amount of water required on farms is
necessarily larger than in cottages, but even the increased
collecting area from the roof of the house and outbuildings
would not give a relatively more abundant supply.
As the water is in constant use, the storage tank need not,
of course, be so large as to hold at one time the whole of the
amount collected during the year. It will be sufficient if it
is one-fourth or one-third this size — that is, if it hold a rainfall
of at least 4 inches. To do this, the tank must have a capa-
city of 3 cubic feet for each square yard covered by the roof
(not of actual roof area). For a country cottage, under the
conditions assumed above, the storage space must be 105 cubic
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RAIN AND RAIN WATER 23
feet. This would be approximately furnished by a tank 6
feet square and 3 feet deep, or by a circular tank 4 feet 8
inches in diameter and 6 feet deep, or 5 feet in diameter and
5 \ feet deep. For larger roof areas the size of the storage
cistern can easily be calculated.
To separate the first portion of the rain water, Roberts*
Rain-Water Separator may be used. " It rejects the dirty
and stores the clean water. It is made of zinc, upon an iron
frame, and the centre part or canter is balanced upon a pivot.
It is self-acting, and directs into a waste pipe the first portion
of the rainfall, which washes off and brings down from the
roofs soot and other impurities. After rain has fallen a
certain time the separator cants and turns the pure water into
the storage tank." The vertical form is used where a single
stack pipe carries the water from the roof to the tank. One
length of the stack pipe is removed, and the separator is in-
serted and fastened to the side of the house. When a build-
ing is provided with several stack pipes connected by an
underground pipe leading to the tank, the horizontal form
should be used. Various sizes of the apparatus are made,
costing from .£3 to ,£6, and it can be fixed by any intelligent
workman. 1
Fig. 3 shows the vertical separator in the position that it
retains when running foul water into the waste pipe during
the first part of a shower, while the roof is yet dirty.
Fig. 4 represents it when it has canted and has begun to
pass the pure water into the storage tank.
One cannot but regret to see in rural districts, where water
famines occur almost every summer, so little effort made to
utilise the rainfall. Any kind of old cask or tank is con-
1 The author some time ago ordered one of the vertical separators to
be affixed to a farmhouse. Shortly afterwards he received a complaint
that very little water was collected, and that it was filthier than before.
Upon examination he found that the workman had so fixed the separator
that the washings of the roof went into the tank, whilst the pure water ran
into the drain.
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24 WATER SUPPLIES
sidered good enough in which to store the rain, and little or
no care is taken to so securely cover the receptacle as to pre-
Fio. 3. Fig. 4.
vent impurities getting in. Separators are not yet generally
used, and therefore the water which is collected is more or less
filthy from the first. Occasionally there is some pretence to
filtration, the stack pipe discharging over a bed of sand and
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RAIN AND RAIN WATER 25
gravel with or without charcoal. For filtration to be of any
service the filtering material must be so fine as to allow the
water to pass through but slowly. As a rule, the more rapid*
the filtration the less the purification (vide Chapter XIII.) ; and
if a small filter is to transmit a heavy rainfall it is evident that
it must be too coarse to be more than a strainer. If finer
material were placed in such a filter chamber, a considerable
portion of every heavy rainfall would run to waste. Where
a separator is used comparatively little sediment is formed
in the tanks, and the water is sufficiently clean and bright for
every purpose save that of drinking. For table purposes it
should be passed through some good form of filter, or the
separated rain water may be collected as it falls in the
receptacle to a filter, and allowed to slowly percolate through
the filtering media into a collecting tank, from which it
can be drawn in any convenient manner. The filter should
be fitted with a loose cover, so that whenever necessary the
top layer of sand can be removed and replaced by fresh, or the
filter be otherwise cleaned. The receptacle receiving the
water from the " separator n should be sufficiently large to
hold \ an inch of rainfall upon the whole collecting area.
If, instead of merely utilising the roofs of buildings for
collecting rain, the surface of a portion of ground be rendered
impervious, any quantity of water may be obtained. In many
cases a plot of ground could be selected at such an elevation
as to supply the mansion, farm, or cottages with water by
gravitation, so saving all the expense of pumps and pump-
ing. Mr. Eardley Bailey Denton, M.I.C.E., writing in The
Field, 18th June 1887, says, "1 inch of rain falling on the
surface of an acre is equivalent to 22,622 gallons ; and sup-
posing that half an acre of land be set apart and rendered
impervious for the collection of rain falling on it during the
six winter months, the amount collected where the rainfall
is least, as in the east of England, during that period would
be about 170,000 gallons (assuming the winter rainfall to be
15 inches), or enough to satisfy the wants of nearly 100 persons
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26 WATER SUPPLIES
for a period of three months (an exceptionally long drought) at
20 gallons a head daily, an ample quantity for all individual
#and household purposes. Tanks can be built at a cost vary-
ing from £3 to £5 per 1000 gallons, and on the chalk formation,
where scarcity is soonest felt, at even less cost. In most
cases a collecting area can be selected free from contamination.
The area upon which the water would be collected need
merely have a concrete floor with cement surface, railed off
to prevent stock running over it, and the storage tank may be
constructed underneath." The above estimate of the amount
of water which could be collected does not appear to be ex-
cessive, and many mansions are now being satisfactorily sup-
plied in this manner. To purify the water a simple filter at
the end of the suction pipe in the underground tank, supple-
mented also by a filter along the course of the house supply,
is recommended. This second filter is fixed below the house
cistern in an accessible position, so that the contents can be
easily cleaned. Unfortunately this plan is too expensive for
groups of cottages — that is to say, the cost per house would
exceed that which a Sanitary Authority can compel the owner
to expend in obtaining a supply (about £8 per cottage). The
roof area of most mansions is so much greater per inhabitant
than the roof area of cottages, that a much more abundant
supply is procurable. Probably 20 square yards per person
is an average in a mansion. This would yield about 1500
gallons per year, or 4 gallons per head per day. The house
cistern should be capable of holding about a week's supply,
and be filled up every day. The need for a cistern so large
is due to the fact that the demand for water is very unequal,
three or four times as much being used some days than
others.
The rainfall is the source of all our water supplies ; but
unless caught upon artificially-prepared surfaces, such as roofs
and specially-prepared cemented surfaces, it is not called rain
water. That which falls upon rocks, either bare or with
little vegetation, when collected is called "upland surface
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RAIN AND RAIN WATER 27
water " ; that which falls upon and is collected from moors is
" moorland water " ; that which runs off the surface of pasture
lands, " surface water from cultivated ground " ; that which
percolates through the surface soil into a j>ervious subsoil is
" subsoil water " ; whilst that which travels through the sub-
soil under impervious strata, so that it can only be reached
by boring through such strata, is " subterranean or deej>-well
water." Where an impervious stratum comes to the surface
and throws out the subsoil water from the pervious stratum
above, a land spring is formed, whilst subterranean water
thrown to the surface in any way forms an "ascending or
deep spring." The waters in streams may be derived from
any one or more of these sources ; river water is usually a
mixture of all, together with sewage and other impurities
received from the towns and villages along its course.
Speaking generally, deep springs yield the purest waters,
and rivers the most impure ; they may be arranged in order
of purity as follows : —
Deep-spring water.
Subterranean or deep-well water.
Upland surface water.
Moorland water.
Subsoil water (if distant from any aggregation of houses).
Land springs.
Surface water from cultivated ground.
River water.
Subsoil water under villages and towns.
The R.P.C. give a lengthy Table of Analyses of care-
fully-collected rain water (78 samples), and of rain water as
ordinarily collected and stored in tanks (8 samples). The
following are the means of their results.
Fresh rain water.
Tank water.
Total Solids .
276
16*8 qrs. per gallon.
Nitric Nitrogen