How Does a Borehole Water Supply Work?

Posted on 02nd April 2019 at 9:18am


What is a borehole?

A borehole is a very narrow hole drilled down through the earth. For irrigation purposes the borehole is drilled to reach the water in an aquifer, it is a much more efficient way of reaching water than digging a well. An aquifer consists of porous rock that is filled with water. Before a borehole is drilled it is important for a survey to be done to ensure that the likelihood of finding water is worth the drilling costs.

In the UK, the advantage of drilling a borehole is that the water extracted by the landowner is free. It is also not subject to hosepipe bans like mains water. However, if more than 20m3 of water per day is to be extracted, the Environment Agency must be informed and a licence applied for. As a single aquifer might have many boreholes drawing from it, the Environment Agency restricts the amount of water that can be extracted to ensure there is sufficient for higher priority needs and that the environment isn’t unnecessarily damaged.

How does a borehole work?

The borehole taps into the underground water source and a pump is used to bring the water to the surface. Generally a borehole will be lined with a porous plastic liner to ensure that it has a very long life and that the sides do not collapse. Borehole pumps are very narrow to allow them to be dropped down the hole that has been drilled. However, when they need servicing they have to be brought back up to the surface, which is time consuming.

How to treat borehole water

Water from a borehole may need to be treated for chemical imbalances eg. high levels of iron and may also need to be filtered to remove sediment. How much filtration is required is dependent on the flows and how clean the water is. As the water had been filtered as descends through the rocks, it is often very clean, in which case a simple screen filter would be added after the pump. Simple screen filters are only a few pounds, for dirtier water, high capacity semi-automatic filters start at several hundred pounds.
How much does a borehole cost?
The cost of the borehole depends on a number of factors including the depth to be drilled and the ease of access for the drilling ring. A ballpark figure for a 60m deep borehole is between £7,000 and £10,000

Could you save money with a private borehole water supply?

How much money you will save depends on how much water you need to use.

A 1,000m2 garden will use 3-4,000 litres a day in summer. With mains water at around £1.50 per m3 this would translate in a daily savings of up to £6.00. If we water for 120 days of the year, this would give an annual saving of £720.

Extracting the maximum permitted amount per day would water around 5,500m2 of garden and save around £4,500 a year. At this point a borehole starts to look an economic option.

Borehole Regulations

The Environment Agency allows the extraction of up to 20m3 of water per day without an extraction licence. Above that amount, a licence must be applied for from the Environment Agency. This is a relatively complex process and will depend on how much water is available in the catchment area, balancing the environmental damage that over-extraction can cause against the benefits.

Records must be kept of how much water is used and these must be reported to the EA. Abstraction covers taking water from rivers, streams, canals or from underground sources via a well or borehole. As a general rule of thumb, if you catch the water before it hits the ground eg. from a roof structure, it is yours. Once it is on the ground then the abstraction regulations apply.

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