The increase in the erratic nature of water supply in most urban centres has led to the need to augment the little water that is available. In Zimbabwe the main sources are wells, boreholes and bulk water suppliers. All have their short falls and as water specialists we feel it is our role to advise the public on the best practices.
Though reasonably priced, these are shallow in depth and in most cases are limited in the amount of water they can supply reliably. In many cases they are a cause of water borne diseases due to poor enclosure and in extreme cases exposure to leaks and spillage of sewer pipes. Best practice is to cover the well to prevent the entry of foreign materials.
BULK WATER SUPPLIERS
This is another source of water which allows areas with limited supply to have potable water delivered in tanks. Bulk water has fixed rates in the range of $50 – $70 for 5000 litres. For areas were the commodity is not available this may be the reasonable source but in the long run the cost of the service is very high. At the moment there isn’t a formal regulatory system, which may compromise the health of consumers. Due care needs to be taken. Suppliers must be reputable companies with vehicles and bowsers that do not compromise the quality of the water.
The issue of boreholes raises a number of questions which we hope we can answer e.g. borehole siting, drilling, capacity testing and installation. To begin with, always work with companies that will leave you a technical report with full details of your borehole such as Thermal Industrial.
This process basically involves assessing the area in order to ascertain the best location to drill your borehole. This will consider the characteristics such as the rock, is it an aquifer aquitard or an aquiclud which will determine the capacity of the rock to hold water as well as to transmit it, which in turn will determine the discharge capacity. A number of devices can be used ascertain these underground conditions. This information is necessary for the driller to know the depth to drill. Please note, there is no set depth for a particular area although water is usually found before 40 metres. An area 50 metres apart from an existing borehole can have totally different conditions.
After siting, the drilling process can begin. There is need for valid siting because a dry hole still needs to be paid for by a client/property owner. A dry hole is not necessarily dry, water be further below the level reached which is usually no more than 40 metres. This challenge can be avoided if a competent siting report has detailed the expected water depth. Usually extra fees are payable after 40 metres, an accurate siting report helps the client budget for that cost. Casing is also another area to consider. This is mainly done to prevent the soil in the hole from collapsing. In most instances full casing is desirable. Pipes fitted must be counted. the size of the pipes which can either be 4 or 6 metre length must also be notes.
This is the determination of the rate of discharge of the hole. This specification is unique to a particular borehole and area. This information is necessary for the accurate determination of the size of pump to be installed. A 12 or 24 hour test can be done and this will determine the actual amount of water available. The size of the pump recommended to be 60% of the determined capacity.
A number of issues need to be considered with respect to installation. Submersible pumps are very sensitive to dry conditions and also the issue of current being received from the power source. One needs to be aware of the duty which is the discharge at a particular elevation difference. If the pump dries the borehole and runs dry this may cause the pump to burn out. There are devices like phase angle relays which can counter this problem. Although that is so, proper sizing of the pump is essential to prevent this. There is also need to have a secure set up ideally using poly pipes which can be easily pulled out. Galvanised pipes require more labour and are hence more secure but more expensive to install. The size of the outlet on the pump should be the basis for the pipework to be used. There is no need for a small outlet discharging into a big size pump as it only increases costs.
The reduction in cost of the plastic tanks has made them readily available. Though that is the case, the major concern is moving the water from the tank/storage unit to the house. In some cases a booster pump can be used or raising the pump may be appropriate. The elevation needs to be noted as this is essential in the pressure required to move the water and it allows water to flow in the pipes and out on the tap, shower etc.
When choosing the booster pump, note the head (elevation) that it can give as well as the maximum discharge it can do so as not to buy a pump that will not give a lower capacity. The increased number of suppliers of these pumps on the market calls for the buyer to pay closer attention. Ideally these specifications should be detailed by a specialist.
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