How Does A Submersible Borehole Pumping System Work - Borehole Basics in Zimbabwe

Before understanding how a Borehole Water System in Zimbabwe works, it is best to understand where the water comes from.

Groundwater is the water found beneath the Earth’s surface which is renewed via precipitation when rainwater or water from other forms of precipitation moves downward to fill up the cracks or spaces in soil and rocks. Groundwater makes up almost all the water on Earth except ocean water and frozen water, accounting for around 95% of all freshwater.

Lakes, rivers, and other surface water make up 3% of all freshwater. The renewal of groundwater depends on various environmental conditions. Groundwater naturally undergoes filtration, but it can get contaminated when it encounters the earth’s surface. Thus, groundwater needs to be protected from pollutants Zimbabwe National Water Authority (ZINWA).

Understanding Aquifers: Water exists underground in what are known as aquifers. Aquifers consist of layers of rock and soil that allow water to flow through their small pores. Groundwater can move from one aquifer to another. In general, groundwater follows permeable pathways within individual aquifers from point of recharge to point of discharge.

When a Borehole is dug, drilled, or bored, the sole purpose is to reach far enough into the aquifer so that water can be accessed and pumped out. Because the location of aquifers and the amount of water in them are rough estimates at best, it is difficult to be certain exactly where and how deep a Borehole needs to be dug. That is why you need to work with Borehole Experts in Zimbabwe on Borehole Siting.

In order for groundwater to be accessed from the surface, the surface of the earth needs to be dug deep enough so that it reaches the aquifer. The hole that is created is known as a Borehole.

1. The Submersible Pump: The Submersible Borehole Pump is the heart of the system. It is what pumps water upward and into the household or designated water system. The two most popular types of pumps used today are jet pumps and submersible pumps. Both pumps rely on centrifugal force in order to force water upward. Spinning rotors, known as impellers, create a vacuum that forces the water upward through the Borehole Casing and into the distribution system. The type of pump required for a Borehole System would depend on the depth of the borehole and the amount of water required for the household.

Jet pumps or Surface Pumps are placed above ground and lift water from the ground through a suction pipe which creates a vacuum with an impeller that drives water through a small nozzle. Because jet pumps use water to pump water, they first need to be primed with flowing water.

Shallow Borehole jet pumps are used for Boreholes that goes down to a depth of 8 metres while deep boreholes jet pumps typically go down 45 metres. Deeper Boreholes would require a submersible pump.

Submersible pumps have a much wider range in-depth and can be used in boreholes as shallow as 8 metres and as deep as 150 metres. As the name implies, submersible pumps are submerged deep in the borehole just under the water level. Most of its energy is dedicated to pushing water upward rather than sucking water from above as in the case with jet pumps.

Submersible pumps are cylindrical in shape, housing the pump motor and a series of impellers that drives water up the pump into the drop pipe. Because of their efficiency, durability, and versatility in borehole depth, most modern borehole systems use submersible pumps over any other pump

2. Pressure Tank: Pressure tanks are used to maintain water pressure throughout the distribution system and to store a reserve water supply so as to relieve the pump of continuous usage. The sizes range from around 40 gallons (180 litres) for domestic use to 21, 000 gallons (8000 litres) or more for industrial use. In conventional pressure tanks, pressure is created by pumping water into the tank until the air in the tank is compressed to typically 40, 50, or 60 psi (pounds per square inch). An air compressor ensures that the air pressure is maintained. When the valve is opened via a tap, the air pressure in the tank forces water out of the tank and into the pipes for distribution.
How Does A Submersible Borehole Pumping System Work - Borehole Basics in Zimbabwe
How Does A Submersible Borehole Pumping System Work - Borehole Basics in Zimbabwe
3. Pressure Switch and Control Box: Borehole pumps, especially submersible pumps, are not meant for around-the-clock usage. Continuous usage would cause unnecessary wear on the pumping mechanism and would rack additional electricity costs. The pressure switch and the control box work in conjunction with the pressure tank to measure the water pressure in the Borehole system so that the pump is only used when the water pressure drops below a certain level.

Typical Borehole systems have a water pressure range of 40-60 psi. When the water pressure drops below 40 psi, the pressure switch turns the pump on, bringing the water pressure back up within range. When the water pressure is at an adequate level, the pressure switch turns the pump back off.

4. Borehole Casing: Borehole casing is made from Polyvinyl Chloride (PVC), is a tube-shaped structure placed in the borehole to maintain the Borehole opening spanning from the target groundwater to the land surface. The casing prevents dirt from contaminating the water and keeps excess water out of the boreholes. It also keeps out contaminants from less desirable groundwater. Borehole Casing comes in various pressure classes. The choice of pressure class to use on your Borehole will depend on the geologic formation.

5. Borehole Cover and Manhole Cover: Borehole caps are placed on top borehole casing to keep out debris, insects, and small animals. They are usually made of steel, aluminium or plastic, and they include a vented screen to equalize the pressure difference between the inside and outside of the Borehole when water is pumped from the Borehole. To prevent overflows from contaminating the borehole, the cap should extend past flood level.
How Does A Borehole Pumping Work - Borehole Basics in Zimbabwe
How Does A Borehole Pumping Work - Borehole Basics in Zimbabwe
While the initial setup of a Borehole Water System can be time-consuming, costly, and will require much inquiry on the homeowner's part, the long-term benefits of Borehole Ownership are undeniable. Private Borehole Ownership saves the cost of monthly water bills, allows for independent control of one's water supply and provides healthy, mineralized water for consumption.

A Submersible pump, whether it be a jet pump that sits above ground or a submersible pump that resides 200 ft below the surface, is the heart of the borehole system and a worthwhile investment for any homesteader.
How Does A Submersible Borehole Pumping System Work - Borehole Basics in Zimbabwe
How Does A Submersible Borehole Pumping System Work - Borehole Basics in Zimbabwe
Thank you for taking the time to read our article on answering the question: 
How Does A Borehole Pumping Work? We would love to hear your feedback. If you have found this article to be useful and are interested in learning more simply give us a call on +263 77 389 897 and we will advise you on the Borehole Submersible Pump that best suits your Installation requirements and Budget.

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Five Facts About Borehole Drilling That You Need To Take Note Of:

1. Know Your Borehole Casings:The Preferred Borehole Casing In Zimbabwe Is Class 9 and 10 (Pressure Classes.)This is because Class 9 and Class 10 Casings are more collapse resistant. The strength of a Casing is often described as collapse resistance.

2. Borehole Drilling Depth: The exact depth, of where the water is located, cannot be established by the drilling contractor nor the Water Surveyor (Borehole Siter).

3. The Is No 100% Guarantee On Water: It is important to note that it is never a 100% guarantee that any hole will yield water, the amount and water quality can also not be guaranteed by the drilling contractor and water surveyor.

4. Borehole Siting or Water Surveying Is Important: Making use of a hydrologist or traditional water diviner will increase your chances of having a successful borehole that will yield a sufficient amount of water.

5. Know The Risks: The risk of the borehole drilling lies with the property owner. The client will still be liable for the drilling costs irrespective of a borehole yielding water or not.

The Cost or Prices For Borehole Drilling in Zimbabwe:

1. Siting: $100.00USD
2. Drilling and Casing: (40 Metres) $1300.00USD - (Using Class 6)
3. AC Electrical Installation: $1000.00USD
4. Solar Pump Installation: $1400.00USD
5. Extra Metres After 40 Metres: USD $45.00USD per metre.
6. 5000 Litre Tank and 4 metre Tank Stand: $1000.00USD
7. Stuck Pump Fishing Out: $180.00USD
8. Capacity Testing: $250.00USD

- Casing with Class 9 Casing incurs an additional $200.00USD.
- Double Casing: $20.00USD per metre.

Note this is the average price borehole companies charge for their services in Zimbabwe, but this figure is subject to changes if conditions are different depending on the construction site.

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