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A water borehole is simply a well that allows you to make use of underground deposits of water called aquifers. Water boreholes are utilised by a wide range of users, usually in commercial and industrial capacities.
Before we can look at how an aquifer is formed we must first look at some of the different types of materials you find in the ground.
A permeable surface is one that allows water to pass through it, and an impermeable surface doesn’t allow water to pass through it. An example of a permeable surface would be soil or gravel and an example of an impermeable surface would be granite or slate.
Because rocks are hard you might be inclined to think that they are impermeable, but not all are. Some rocks have tightly bound particles that don’t allow water to move through them, whilst others have round loosely bound particles that allow water to pass through them. Permeable rocks are generally porous and are crumblier, one example being sandstone.
So why does the makeup of the ground matter? Well, when it rains, water seeps into the ground travelling through permeable materials deep into the earth, sometimes even thousands of meters deep.
When the water reaches an impermeable layer of material, the water can’t travel down any further and so starts to collect on top of the impermeable material. These water filled sections of soil sand and rock are what makes up an aquifer.
To access the aquifer a specialist drilling company will need to come and drill a vertical hole into the ground to the depth of the aquifer. A special casing will need to be inserted into the hole to keep debris from falling in and to stop it from collapsing.
Once the hole is drilled and everything is in place, the water pump is ready to be inserted. A submersible pump, fitted with a sediment screen, attached to a length of pipe is lowered into the borehole to reach below the water level. This serves to pump water out of the aquifer to the surface.
Having a viable borehole isn’t quite as simple as having water underground, there needs to be a great enough quantity for your needs. Whether or not there is enough water will depend on how much water is entering the aquifer, as well as the characteristics of the base impermeable layer.
Groundwater acts in the same way as surface water, in that gravity causes it to flow downwards. This means that water collects in the deepest point of the impermeable layer. The level of this water (the water table) is dictated by the amount of water feeding the aquifer.
Not only do you need to consider the amount of water available, you also need to consider the depth of the aquifer. In some places you may only need to drill 20 meters to reach water, however, in others you may need to drill 300 meters. The cost of drilling increases as the depth increases and so it can be economically unviable to pursue a water borehole.
So why does the makeup of the ground matter? Well, when it rains, water seeps into the ground travelling through permeable materials deep into the earth, sometimes even thousands of meters deep.
When the water reaches an impermeable layer of material, the water can’t travel down any further and so starts to collect on top of the impermeable material. These water filled sections of soil sand and rock are known as aquifers, which is what’s needed for a water borehole.
Typically, no. In many places, such as the UK, you are able to draw some water without applying for any sort of license. However, when drawing large quantities of water a permit is generally required.
The requirement for a permit is there to protect the environment. When drawing large quantities of water, consideration must be given to the effect on the local water table.
Drawing large quantities of water from aquifers can drop the water table, which in turn drops local river and lake levels. To ensure this doesn’t happen legislation requires thorough and precise testing of local water levels when drawing large quantities.