•004
•78 „ „
Chlorine .
•43
1*6 „ ,,
Hardness
•42
7*9 „ „
Free Ammonia
•50
1*15 pts. per million
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CHAPTER III
SURFACE WATER
Igneous, Metamorphic, Cambrian, Silurian, and Devonian
rocks resemble each other in being practically impervious, and
very slightly acted upon by water ; and the districts where such
rocks are exposed are usually wild and mountainous, and in
Great Britain at least have a rainfall much above the average.
Rain falling upon such surfaces rapidly runs off, forming
rivulets and streams, pools and lakes, the water from which
differs but little from that of the rain from which it is derived.
Certain limestones of the Silurian and Devonian systems,
though very compact and hard, however yield an appreciable
trace of carbonate of lime to the water, causing it to have a
hardness of from 6 to 10 or more degrees. The hardest
rocks undergo a process of weathering, by the exposure
of their surfaces to the action of the air and water. By
the alternate freezing and thawing of water in the minute
interstices, the superficial layers become disintegrated and
yield a little soluble matter to the rain falling thereon. If
the surface be very steep, the debris is washed away as formed ;
if not, it gradually accumulates, until there is sufficient to
enable lichens and mosses to flourish. The decay of these
plants furnishes mould or humus, upon which larger and more
highly-organised plants may grow, and these by their death
and decay furnish the beds of peat so common in certain
districts. The rain falling upon such plant-covered surfaces
is in part retained, some being returned to the atmosphere by
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SURFACE WATER 29
evaporation from the surface of the soil, and from the fronds
and leaves of the plants covering it, the remainder slowly find-
ing its way to lower levels, and ultimately into the streams
and pools. Only during heavy rains will any quantity run
directly off the surface. From the bare rocks, since the rain
immediately flows away, comparatively little is lost by evapora-
tion or absorption ; rivulets and streams are quickly formed
and almost as quickly disappear. Where the rocks are
covered with vegetation the streams are more permanent,
though fluctuating greatly. Much of the water, being retained
for a time in the spongy mass of vegetable debris clothing the
rock, is enabled to take up a certain amount of organic
matter, sufficient frequently to impart a brownish colour and
a peculiar bitter "peaty" flavour. These impurities are
solely of vegetable origin, and unless excessive in quantity
appear to have no injurious effect whatever upon the health.
The igneous rocks of Devon and Cornwall yield a water
containing very little inorganic matter ; but as peat is
abundant in these districts, the organic matter derived
therefrom may be considerable. Containing little or no
carbonate of lime, they usually act freely upon lead
(vide Tables of Analyses).
The Metamorphic, Cambrian, Silurian, and Devonian rocks,
exposed in Wales and neighbouring counties, Westmore-
land, Cumberland, Devon, and Cornwall, yield water very
similar from a hygienic point of view to that from the
igneous rocks. The metamorphic rocks (quartz, mica
schist, gneiss, granite, and crystalline limestone) may
be said to be absolutely impervious, as may also the
slates of the other series. The sandstones, however, are
more or less porous, and absorb some portion of the rain-
fall. The calcareous rocks of the Silurian and Devonian
systems are exceedingly compact, and the water from
their surface is but little harder than that from the non-
calcareous rocks.
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3 o WATER SUPPLIES
The non - calcareous carboniferous rocks (Yoredale rocks,
millstone grits and coal measures) occur in South Wales,
Derbyshire, Yorkshire, Lancashire, and North Stafford-
shire, and are but slightly pervious. A considerable
proportion of the rainfall on the slopes of the hills finds
its way into the rivulets and streams, some of which are
utilised for feeding reservoirs for supplying many of our
manufacturing towns with water. Certain of these
waters are exceedingly soft, the average hardness only
being 6°. They are therefore admirably adapted for use
in steam boilers and for most manufacturing purposes.
They are frequently peaty and turbid, but when
carefully filtered usually form satisfactory domestic
supplies. In certain districts the water is frequently
acid, and then acts powerfully on lead. It is water
from these sources which has produced the extensive
prevalence of lead -poisoning in the Lancashire and
Yorkshire towns.
The calcareous carboniferous rocks (carboniferous or mount-
ain limestone and limestone shales) of Northumberland,
North Yorkshire, Lancashire, and Mid-Derbyshire yield
a water of a moderate degree of hardness, not so well
adapted for many manufacturing purposes, but not too
hard for domestic use, and free from any solvent action
upon lead. The beds of limestone and sandstone in the
coal measures are more freely acted upon by water,
and that derived from the surface may be excessively
hard, even exceeding 50°. 16° is given as the average.
When the hardness is excessive the water is, of course,
unsuitable for domestic use and for most manufacturing
purposes.
The secondary rocks " stretch across England from the mouth of
the Tees to the mouth of the Exe, with a branch running
to the mouth of the Mersey." The lias, new red sand-
stone, conglomerate sandstone, and magnesian limestone
formations yield from their uplands a water closely
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SURFACE WATER 31
resembling that from the mountain limestone (Tables I.
and IL include analyses of waters from all the above-
mentioned formations).
Where any of these formations are covered with soil in a
state of cultivation, the surface water is often much altered
in character, especially if the soil be calcareous. The hardness
is then considerably increased. All are liable to contain larger
traces of organic matter, some of which will be of animal
origin. Nitrates, which are present in infinitesimal amount,
if at all, in water from barren rocks, are always found, and
may occur in considerable quantities, if the soil be manured.
The chlorides also will increase in proportion to the number
of men and animals living upon the gathering ground.
In this country the amount of chlorine in the rainfall varies
so considerably with the distance from the ocean, prevailing
direction of the wind, etc., that it is only over very localised
areas that this factor can be utilised for determining whether a
water be polluted or not ; but on continents like North America,
large areas (whole States in fact) are so slightly affected by
these conditions that the amount of chlorine may be used
for ascertaining and calculating approximately the amount of
pollution. In Massachusetts the whole of the surface of the
country, with the exception of a very small portion, is non-
calcareous, and the surface waters vary but little in composition
if unpolluted, the amount of chlorine decreasing continuously
from the coast inland. In a report on the State water supplies,
1887-1890, the Commissioners state that "in a general way
four families or twenty persons per square mile will add, on an
average, '01 of a part per 100,000 of chlorine to the water
flowing from this area, and that a much smaller population will
have the same effect during seasons of low flow." They
therefore tabulate the ninety surface waters of the State that
are used for public drinking supplies according to whether
the amount of chlorine they contain is in excess of the normal
or not. In twenty-six there was no excess of chlorine ; in
twenty-three the excess was so slight that they could not say
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32 WATER SUPPLIES
that they were in the least polluted by household waste. The
excess of chlorine in the others indicated that they contained
from one to five per cent of water, containing as much salt as
ordinary sewage. The average composition of the above
three groups is included in the Table of Analyses, page 38.
The other indications of pollution in drinking waters from
upland surfaces and other sources will be fully considered later.
Surface water may not only be discoloured by draining from
peat-clothed rocks, but may also be turbid, especially after
rain. When stored in reservoirs, it occasionally, especially in
the late summer and autumn, acquires a disagreeable odour
and taste, from the presence of algae and other low forms of
vegetable life. The Massachusetts Commissioners found that
polluted waters were most frequently so affected, and especially
if stored in shallow ponds, lakes, or reservoirs. Pure water in
deep lakes and reservoirs, though by no means exempt, rarely
acquires bad tastes or odours.
Pools are collections of water of limited extent in the
hollows of the rocks in hilly districts, and the water may have
the ordinary character of surface water from the particular
formation. Usually, however, they contain accumulations of
dead and decaying vegetable matters, which render them
impure. Ponds are usually artificial reservoirs formed by
making an excavation in the impervious subsoil, or by lining
with some impervious material, such as clay, a cavity made in
the pervious superficial stratum, and storing water which has
drained from the ground around. Such waters are rarely fit
for domestic use, not only on account of the vegetable matters
contained therein, but on account of their liability to pollution
by cattle, by manure on the ground within their drainage area,
etc. Being shallow, the whole mass of water may be frozen
during a severe and continued frost, and any contained fish
will perish ; afterwards when the ice melts these will decompose
and foul the water. Several instances of this kind have come
under my notice in districts where the inhabitants depend
upon ponds for their supply of water.
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SURFACE WATER 33
Suspended matters in surface waters may be removed by con-
tinued storage in large reservoirs or lakes, when time is given
for the whole to subside, or by filtration through sand, which,
however, is troublesome and somewhat expensive. The Massa-
chusetts Commissioners point out " that when water is taken
from the ground near streams and lakes it is often to a large
extent surface water so thoroughly filtered that it cannot be
distinguished from the natural ground water. This method
of purification by natural filtration is an excellent one to
adopt where there is a sufficient area of porous ground adjoin-
ing the surface water source."
The advantages of converting lakes into reservoirs for
storing water over the construction of artificial reservoirs are
so great that several towns have already adopted this plan.
Glasgow is supplied with water from Loch Katrine ; Liverpool,
and several other towns, from Lake Vyrnwy in Wales ; and
Manchester from Thirlmere in Cumberland. As an example
of a smaller town Aberystwith in North Wales may be
quoted; it derives its supply of water from that portion
of the rainfall on Plynlimmon which runs into the Llyn
Llygad Rheidol Lake. The following account is taken in
part from evidence given at an inquiry held by the Local
Government Board, and contains many points of interest.
The inquiry was held to sanction a loan of £16,000 to
carry out the work. At the present time the town has a
resident population of 10,000, and in summer a considerable
number of visitors reside there. The scheme was completed in
1883, and the town has now an abundant supply of water of
unexceptionable purity.
" The source of supply is the Llyn Llygad Rheidol Lake,
situated on Mount Plynlimmon, 16£ miles from Aberystwith,
and about 1650 feet above the sea. The wild nature of the
country renders the possibility of pollution remote. The
area of the lake is \\\ acres, its greatest depth 60 feet, and
the available storage capacity, supposing the bank is raised,
as proposed, 1 foot, and only 15 feet of water is drawn off, is
D
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34 WATER SUPPLIES
nearly 40,000,000 gallons. This is equivalent to eighty days'
supply for a population of 25,000 at 20 gallons per head
(that is, for about twice the present population (1892),
summer visitors included). This would be if no rain were to
fall on the mountain for that length of time — a supposition
hardly ever likely to be realised. Plynlimmon rises about
2500 feet above the sea, and is the highest peak in this part
of Wales. The warm winds from the south-west and west,
coming laden with moisture, impinge on the mountain, and
their temperature being suddenly reduced, copious falls of
dew and rain take place. The lake is actually fed with rain
that falls on the very summit of Plynlimmon, and it would
only be in a most extraordinary season of drought that no
rain, would fall for more than 2£ months. The area draining
into the lake is 133 acres. The actual rainfall is unknown,
but Mr. Symons (the first authority on the subject) puts it
at over 75 inches. At Nantiago Lead Mine, 800 or more
feet below Plynlimmon, it was 92 inches in 1878, so that it
may be 1 20 inches or even more at the summit of the mountain.
The very moderate rainfall of 60 inches only is assumed. Very
little would be lost by evaporation, the slopes of the mountain
being so great that the water runs off most rapidly; and
very little would be lost by percolation, as the mountain
consists of Bala rock, the upper member of the lower Silurian
beds, a hard and more or less impermeable formation. If,
then, 60 inches only be taken as the available rainfall over
133 acres, the quantity flowing into the lake would be over
180,000,000 gallons, very nearly a year's supply at 500,000
gallons daily. If the available rainfall be 100 inches per
annum (as indicated by gaugings of the outflow from the
lake), the supply would be 300,000,000 gallons yearly. The
water will be carried from the lake to Aberystwith in an
iron main 8 inches in diameter. Such a main, with the
minimum gradient obtainable for it, will deliver more than
half a million gallons daily. The water, before being dis-
tributed in the town, will be discharged into a service
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SURFACE WATER 35
reservoir, two-thirds of a mile from the town and 130 feet
above the highest building in the place. The general
pressure throughout the town will be equal to a head of 200
feet. The capacity of the reservoir will be 1,000,000 gallons.
From the service reservoir the water will be distributed to
the town by a 10-inch main." The following is an abstract
of the estimate : —
Cast-iron pipes, 34,117 cwts., at 5s. per cwt. £8529 5
10-inch main from service reservoir, 2338 cwts. 584 10
Excavating trenches for pipes, and refilling
28,804 lineal yards at prices varying from
2s. in rock to 6d. in soft soil per yard . 1514 8 7
Laying pipes and jointing them . . 1214 8
Extra for junctions and special pipes . . 110
Carnage of pipes 1055 14
Sluice valves, flushing valves, air cocks, etc. . 188 9
Posts to indicate line of main . . . 25
Pressure-reducing tanks or break valves, and
fixing ditto 217 10
"Works at the lake for drawing off the water . 185
Service reservoir, with valves, pipes, etc., complete 2019 11 6
Contingencies, law charges, and engineering
at 7J per cent 1173 4 6
Total . . . £16,816 13 3
The works were duly executed, but the estimate was exceeded
by about £1000, a detour with the water main having to be
made on account of the peaty nature of the ground. It will
be noted that no land had to be purchased, and that no com-
pensation water had to be provided, both important matters
for consideration when a public water supply is being
provided.
At the Congress of the British Institute of Public Health
held last year (1893), in Edinburgh, the engineer to the
City Waterworks gave a description of the Loch Katrine
Waterworks supplying Glasgow. The paper contains much
that is interesting, and to it I am indebted for the follow-
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36 WATER SUPPLIES
iiig particulars. When the scheme was first propounded,
Glasgow had a population of 350,000, and it was estimated
that it would increase to 760,000 in 1900, and that the
consumption of water would then be 30,000,000 gallons per
day. The works were estimated to bring 50,000,000 gallons
per day. However, both these estimates have proved
erroneous, since the population now being supplied with water
is 860,000, and the consumption of water has risen from 40 to
50 gallons per head, so that 43,000,000 gallons are now used
every day. The increased quantity used is attributed to
several factors : the introduction of baths into the houses of
the well-to-do working classes ; the compulsory fitting up of
water-closets in even the smallest class of houses; the increase
of public urinals, watering-troughs for cattle, drinking and
ornamental fountains; the introduction of several large public
swimming baths. Loch Katrine is 368 feet above the sea.
The area of the loch is 4 J square miles, and its drainage area
36 \ square miles. By means of a small masonry dam at the
outlet the loch has been raised 4 feet above the old summer
level, and can be drawn down 3 feet below that level. In
this range of 7 feet there is comprised a storage of
5,623,000,000 gallons, or 102 days' supply. The surround-
ing hills rise to a height of from 2300 to nearly 3000 feet ;
and as a result of this and the proximity of the district to
the west coast, which first receives the moist south-west winds
of the Atlantic, the rainfall is very large. At Glengyle, at
the top of the loch, the fall is frequently over 100 inches per
annum, and the driest year during the last 40 years (1880)
yielded 69 inches. The loch is so deep that the water never
freezes except in shallow and sheltered bays. Temperature
observations made in 1885 and 1886 show that the water
reached its lowest temperature of 38*7° F. near the bottom,
in March, whilst at the top it was 38*1, and that during the
rest of the year the surface water was warmer than the deep
water. Geologically the district round the lake consists of
metamorphosed mica schist of the lower Silurian system,
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SURFACE WATER 37
yielding very little mineral matter to the rain falling upon
it. The district is practically uninhabited, and by a pay-
ment of £17,600 to the proprietors of the land they have
surrendered all rights of feuing and of erecting houses, or
of allowing additional steamers or boats to ply on the lake.
There is much peat on the hill tops, and in times of flood the
streams are highly coloured, but the relatively large size of
the loch and its great depth have an important influence in
removing the peaty stain. Analysis shows that it is a very
pure water, exceedingly soft (hardness under 1°). Notwith-
standing this no case of lead-poisoning through using it has
ever been reported. A service reservoir 8 miles from
Glasgow holds eleven days' supply. The aqueduct was
expected to pass 50,000,000 of gallons per day, but the
effect of the roughness of the channel in retarding the flow
(friction) was much more than had been anticipated, and the
flow is only 42,000,000. The total cost of the works, in-
cluding llf miles of tunnelling, 10 J miles open cutting and
bridges, 13| miles cast-iron syphon pipes across valleys, and
piping within distribution area, has been close upon
£1,500,000. This also includes works carried out at other
lochs to provide 40,000,000 gallons of compensation water.
An extension of these works is now being carried out which,
it is estimated, will allow of 100,000,000 gallons of water
per day being drawn from the loch for the supply of the
city, at an additional cost of £1,150,000. The domestic
water-rate, which in 1856 was Is. 2d. per £1 of rental, has
been reduced to 6d. per £1.
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CHAPTEK IV
SUBSOIL WATER
The subsoil or stratum immediately underlying the surface
soil may be of a pervious or impervious character. If pervious
a considerable portion of the rain falling upon the soil will
pass down into it, if impervious only a relatively small
portion will percolate, the larger portion running off as sur-
Fio. 5.— a, Pervious subsoil ; a\ Portion saturated with water; a % Impervious
stratum ; c, Spring.
face water. Where such an impervious rock occurs covered
only with the spongy debris of vegetation, saturated with
water, we have bogs, marshes, and swamps. The district
will probably be malarial and the water of a dangerous
character. Where a pervious subsoil of sand, gravel, chalk,
limestone, sandstone, or other rock overlies an impervious
rock such as clay, granite, hard limestone, etc., a portion of
nearly every rainfall enters the subsoil, and being held up
by the impervious layer below tends to accumulate. The
water thus held in the interstices of the rocks lying imme-
diately beneath the soil is "subsoil" or "ground" water.
Where the pervious subsoil fills in a hollow in the more im-
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42 WATER SUPPLIES
pervious stratum, as in so-called pockets of gravel, the ground
may become waterlogged — that is, completely saturated
with water. If, however, at any one or more points the edge
of the containing basin is depressed, water will overflow, form-
ing a spring. Such overflow will only take place when the
water in the porous rock has its surface level raised above that
of the outlet. The portion below this will still remain stagnant.
Where the porous subsoil rests upon a flat or sloping imper-