Many people are inclined to think that waste of this kind is not a bad thing, as it must help to keep the drains flushed. Field points out that this is quite a mistake. A small dribble of water from a leaky pipe or a leaky tap, though it will waste a great deal of water in the course of 24 hours, is perfectly useless for flushing the drains. What is wanted for this is the sudden discharge of a large quantity of water. The dribble of water from leaky pipes and taps does no good in any way, but simply wastes what might be usefully employed, and in many cases causes a supply to run short which would otherwise be ample for all legitimate uses. Another point that it is difficult to realise is the large quantity of water which will run to waste through what is apparently a very small leak. The quantity leaking looks so small in comparison with the quantity running when a tap is open, that one is inclined to think it perfectly insignificant, forgetting that the leakage goes on continuously night and day, whereas the tap is only open for a few minutes. In country houses, where it is often difficult to obtain a sufficient supply of water, it is particularly important to bear in mind the serious influence that leaky pipes and taps have on the consumption, and never to allow such leakage to go on for any length of time.
While useless waste should be prevented, it is most important that the legitimate use of water should be encouraged in every way. As Dr. Richardson has well pointed out, absolute cleanliness, properly understood, is the beginning and the end of sanitary design, and thorough cleanliness, of course, can never be obtained without an ample water supply. Not only should there be sufficient water for baths, lavatories, and washing of all kinds, but there should be a liberal allowance for flushing water-closets and all other sanitary appliances. Taking these sanitary considerations into account, as well as giving due weight to the observations which have been made by engineers and others on the quantity of water actually used in houses under different circumstances, it may be assumed that, if waste is efficiently prevented, a supply of 20-25 gallons per head per diem is sufficient in ordinary cases for houses with baths and water-closets. If horses are kept, a separate allowance should be made for them, and for stable purposes (a useful approximate rule being to reckon a horse as a man); and if water is used for watering gardens or ornamental purposes, this must also be reckoned separately. If earth-closets are adopted instead of water-closets, less water will be required, and 15-20 gallons per head per diem will be sufficient. In cottages with earth or other dry closets, the quantity of water required will be still less: 10 gallons per head will be an ample supply, and even 5-6 gallons may do in cases where it is absolutely necessary to limit the quantity used.
Sources of Supply.—Water for country houses is, in the vast majority of cases, derived from springs or wells. Rain-water collected from roofs is very frequently used as an auxiliary, and occasionally as the main supply. There are instances in which the supply is taken from streams or rivers, and even some in which water running off the surface of the ground is collected in “impounding reservoirs” (a mode often adopted for the water supply of towns); but these cases are exceptional, and attention will here be confined to springs, wells, and roof-water.
The real source of all fresh water supply is rain. Springs and wells form no exception to this rule, though in their case the connection with the rainfall is not so clear at first sight as it is in the case of streams and open watercourses, because the passages by which the rain reaches springs or wells are not visible, and heavy rainfalls often have no apparent effect on their yield. In various parts of the country occur curious intermittent springs (locally called “bournes”), which burst out in some years and not in others, and the connection between which and the rainfall is still more obscure. Rain-water, before it issues from the ground as springs, accumulates in the porous strata beneath, and forms, as it were, large underground reservoirs; it is from these reservoirs that wells, sunk into the porous strata, derive their supply.
The amount of rain varies enormously in different parts of the world, some districts being either absolutely rainless, or having only a very few inches of rain in the year, whereas others have some hundreds of inches in the year. Even in England itself there is considerable variation. The average rainfall for the whole country is about 30 inches a year, but the amount in different parts of the country varies from about 20 inches to nearly 200 inches a year. The eastern side of England, as Field remarks, has much less rain than the western side, and, roughly speaking, if a line be drawn from Portsmouth to Newcastle-on-Tyne, it will divide the country into a dry portion and a wet portion. The portion of the country on the east of this imaginary line will (with the exception of the south coast, which is wetter) have only 25 inches of rain or less, and the portion on the west of the line will have from 30 to 50 inches, with much larger amount in the Cumberland and Welsh mountains, and at Dartmoor.
The rainfall of the wettest year is about double that of the driest year. This gives a very useful rule for roughly ascertaining the extreme rainfalls, which are really more useful for the purpose of water supply than the rainfall for an average year. The fall in the driest year may be assumed to be one-third less than the average, and for the wettest one-third more. Thus, with an average rainfall of 30 inches, the fall of the driest year would be 20 inches, and that of the wettest year 40 inches.
A portion only of the total rain which falls is available for water supply, as there is always more or less loss. In the case of rain falling on roofs, the loss is comparatively small, but in the case of rain falling on the surface of the earth the loss is considerable. The latter is disposed of in three different ways: part of it runs directly into open watercourses and streams, part is taken up by vegetation or lost by evaporation, and part percolates through the surface ground and accumulates in the water-bearing strata which feed the springs and wells.
From observations made on the amount of percolation in different cases, it has been found that the amount of percolation does not depend so much on the amount of rain as on the conditions under which it falls. By far the greater portion of the percolation takes place in winter and comparatively little in summer, the reason being that in winter the ground is wet, evaporation is small, and vegetation is inactive, so that a large proportion of the rain sinks into the ground; whereas in summer the reverse is the case, so that most of the rain is taken up before it can percolate. So great is the difference between summer and winter as regards percolation, that one may generally leave the summer rainfall altogether out of consideration, and assume that, in this country, it depends on the amount of rain which falls during the six months from October to March, whether the underground store of water will be fully replenished or not.
The height of the accumulated underground water is indicated by the level at which water stands in wells: and it is found that this height varies considerably, the variations usually following a regular course: the water is generally lowest in October and November, it then rises till it reaches its highest point in February or March, and after this it falls slowly till the following autumn.
A condition to be studied in selecting a spring as a source of water supply is its “seasonal” variation. As Field points out, a spring which will give an ample quantity of water in the winter may give an insufficient quantity in the autumn, so that the measurement of a spring in winter should never be depended on for determining whether it will do as a source of water supply. The only safe way is to wait till the autumn yield has been ascertained; even then an allowance must be made for the previous winter, if it has been a very wet one, the yield of the spring becoming abnormally high.