Water can be obtained from the following sources:
(i) Stored Rain Water. Where no other source of water is available for the homestead, tanks are filled during rain from roofs of buildings or specially constructed concrete catchment areas. From these sources the water is taken to where it is required by gravity or pumping. The stored rain water is liable to contamination and the supply is also liable to fail in prolonged dry periods, so that it can only be regarded as an unsatisfactory source of supply. Stored rain water would not be sufficient in quantity for the stock and general farm purposes, but it might be enough for the homestead. A large underground concrete tank with a roof is the best form of storage for rain water as the water is kept clean and cool.
(ii) Surface Run-off. In regions where no other suitable source exists, water for stock is obtained by building a dam across a pulley or depression, thus impounding water that runs off during heavy rain to form a lake or pond. The dams are usually built of earth, a bulldozer being used in their construction. The stock may have direct access to the pond, but it is far better to build a fence around it to keep the stock out and pipe the water to troughs. This prevents fouling the surroundings of the pond and contamination of water, which might lead to the spreading of stock diseases. As this form of supply is liable to contamination it should not be used for human consumption.
(iii) Stock Water Races. In Canterbury and some other parts of New Zealand, water is taken across country from the rivers through water races, and delivered to the farms for consumption by stock. Although this is usually a reliable supply, it is liable to become contaminated, and may possibly spread stock diseases. It is certainly unfit for human consumption unless purified.
(iv) Stream and River Water. Water may be pumped or conveyed by gravity from streams or rivers and used for stock watering and the homestead, although pollution may render it unfit for the latter purpose unless it is purified. It may be necessary to dam a stream to provide a reservoir which gives storage and allows settlement of the water. Before damming or taking water from a stream, it is necessary to consult the authority that controls the stream, and comply with its requirements. The rights of other users must be respected.
(v) Springs. Water sometimes rises naturally to the surface of the ground to form a spring, and if the flow is adequate the water may be stored and delivered where required on the farm or homestead. Spring water, if it can be collected and stored without contamination, is often sufficiently pure for human consumption, but great care should be taken to make certain that it is satisfactory before using it.
(vi) Driven or Drilled Pipe Wells. In some districts pipes can be driven into the ground until a source of water is reached. This may be an artesian well, where a water-bearing stratum is tapped in which the water is under sufficient pressure to rise to the surface of the ground through the pipe. Alternatively, it may be necessary to pump the water from the well. The well pipes or “casings” are at least 2 in. in diameter and often more. Large wells or wells in rock may be drilled by a percussion or rotary process, the casing being driven down behind the drill.
In some districts the depth at which water can be obtained is known by experience, and well-sinkers can estimate it fairly accurately, but in districts where few if any wells have been sunk it is impossible to be certain whether or not water will be obtained. Geologists may be able to advise on the probable depth of water-bearing layers, but no reliance should be placed on so-called water diviners. Water divining has been tested scientifically on many occasions, both in New Zealand and overseas, and has been proved quite unreliable for finding water. Water from driven pipe wells is usually pure enough for human consumption, but should be tested before being used.
(vii) Open Wells. Many years ago it was common to dig wells several feet in diameter to a depth at which a satisfactory supply of water was obtained. The wells were dug by hand and lined with wood, brick, concrete, or stone, for the top 10 ft. or so to prevent ingress of surface water, and further if necessary to prevent caving in.
The water may be pumped from these wells, but few open wells have been constructed in recent years, as they are very liable to contamination and are difficult and expensive to dig. They have been largely superseded by driven pipe wells, but they have the advantage of containing a large volume of water, thus permitting more rapid pumping. Modern mechanised methods of sinking and lining open wells may make them popular again for stock water or irrigation.
Whatever the source of water, if it is for human consumption, every precaution should be taken to prevent it from becoming contaminated either at the source or in conveyance or storage. For example, supplies from springs should be protected by fencing the area against access by stock or persons, and by diverting surface run-off from higher ground by the construction of a diversion ditch. Open wells should be sited well away from septic tanks and properly lined to prevent ingress of surface water. Underground storage tanks should be covered with a sound roof and should be constructed so that surface water or underground water cannot enter.
Water supply from roofs
The amount of runoff from a roof may be calculated from the following relationship
YR = R x Ax 0.9
Where YR = Annual yield from roof (litre)
R = Annual rainfall (millimetre)
A = Area of roof (square metre)
If the average annual rainfall is 600 millimetres and the roof area is 250 square metres, then
YR = 600 x 250 x 0.9
=135,000 L
Evaporation directly from the roof surface at the start of rain , will reduce the potential yield, as will splash and overtopping of the collection plumbing. The factor of 0.9 assumes that approximately 90% of rain falling on the roof can be channeled into a storage tank.
Rainfall replenishment on a regular basis make it possible for more water to be used over the year than actual tank capacity. Therefore, it is advantageous to calculate inputs and outputs on a monthly basis. Total storage capacity should be able to cover periods of low rainfall identified from local rainfall records.
The adequacy of a particular sized tank for household need is determined from a monthly assessment of the expected use compared to expected runoff from the roof. Assume the tank is full at the start of September. Calculate the difference between use and inflow for each month and the amount of water in the tank at the end of the month. Carry this figure over to the start of the next month, but remember that excess water will be lost as overflow. Complete for one whole year and assess whether that sized tank is likely to be suitable.
Although monthly average rainfalls are published for Victoria, the actual rainfall for each month can vary widely from year to year. Too much reliance on the published average figures is therefore not advisable when assessing annual inflows.
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