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Bore Wells

Bores or wells for supplying water from the ground

Bores and wells are used all over the world to pump water from the ground.

What is a bore, how does it workand how deep should it be.

How do we install one and what sort of pumps can be used.

Where does your water come from?

bore well

It is amazing how many people have no idea where their water comes from.

Most of us know better than to drink local water or clean our teeth in it but we still wash our dishes and ourselves in it without knowing where it comes from.

Some of us are fortunate enough to have a government reticulated water supply which is treated and supposed to be fairly safe.

Unfortunately, due to the many leaks in the pipes of the distribution network, we have to assume there can be contamination from the surrounding groundwater. In crowded neighbourhoods will probably be close to septic tanks along the way.

Many people across the world get their household water from a well or, far more likely these days, a bore.

What is a bore well?

A bore is a hole, usually 4 or 6 dim, drilled into the ground. A pump is placed at the bottom to pump water up to your house. It is, in effect, a small diameter well but there are fundamental differences that make a bore more attractive than a well. The kids can’t fall down it for a start.

But first I used the word ‘4 dim’ which actually means 4 inches diameter. Plumbing pipework in many parts of the world is often still measured in inches. Inches are useful, if you don’t have a ruler an inch is the width of a man’s thumb.

Wells are usually dug by hand. I recently came across a well being dug by a team of welldiggers. 1 metre in diameter the diggers got down 15 metres when the air got so foul that the digger at the bottom was passing out and the well digging had to stop. The well, still dry, was abandoned.

Bores are drilled by a boring machine and can go much deeper than wells without being affected by noxious fumes.

The good thing about bores is that you can make them very deep which gives two advantages:

  1. You can make sure you reach well into the water table below so you will still have water even during very dry spells.
  2. Water is filtered as it seeps down through the ground, the greater the depth the cleaner the water (generally speaking but not always)

Bores vary considerably in depth depending on the geology of the area but a typical bore can be anything from 20 to 50 metres deep. In some areas such as in limestone areas bores may go much deeper and 130 metres is not unusual. How deep depends on where you are and the type of land you are in. For most of us the ground is alluvial deposits so we drill our bore through clays and soils. Where the ground is limestone which is full of fissures and cavities, the water flows away easily and so the surface of the groundwater is deep within the rock. To get water you have to drill down to below the watertable, the level of the permanent water in the ground.

Bores provide filtered water

Bores and wells work in the same basic way. We put a tube into the ground to achieve two aims: firstly to give us access to water that lies deep within the earth, secondly to collect clean water that has been filtered by flowing down through the earth. The first aim is obvious, the second depends on sealing the sides of the tube so that water has to flow down through the earth before it can enter through the bottom of the tube.

Installing a bore

First we must choose the site fro a bore to be well away from any ground pollution such as septic tanks or pig sties. We will need an electrical supply for the pump which will need to be placed close to the bore. We also need to think about the plumbing to your house and a storage tank if you are going to use one.

To install a bore we drill a hole and we slide a pipe or a sleeve down the hole to seal it. This sleeve must not go right to the bottom of the bore, it has to have enough bare earth at the bottom to allow the water to seep into the hole as fast as you are going to pump it out. In a 50 metre deep bore we might put in a 45 metre long sleeve giving us a healthy 5 metres of open hole at the bottom to collect water.

How to find water

But first we must find some water and this can be a bit of a hit and miss affair. You can do it the old fashioned way by calling in a water diviner who wanders around delicately holding a twig until he ‘feels’ the twitch of the water. These days you can be far more scientific and have a hydrogeological survey done, expensive but far more reliable and, if water is key to your business success, then perhaps the cost is well justified. Drilling bores can be expensive particularly through rock, doing a proper survey beforehand makes sense.

But then there are of course those mysterious things ‘aquifers’, water bearing rock, the holy grail of the water diviner. If you hit an aquifer you can usually find a good source of water but aquifers may have a downside. An aquifer may have fairly freely flowing water in an underground stream and is more likely to be polluted than water that has been filtered by seeping slowly down through the earth. Years ago I came across a man who had a bore which, at 50 metres, was fairly deep for a ricefield area. We tested his water and found serious lead contamination. In an area like this the lead was most likely coming from some man made pollution, perhaps a garage with old car batteries somewhere upstream. He had happened to hit an underground stream. The solution was to drill the bore a bit deeper or even shallower to avoid the problem water source.

Pumps for Bore wells

Alright so we have found the right place, drilled a hole and put in a sleeve, all we have to do now is get the water out but we have a problem. A normal water pump is probably good for moving water up to say 10 metres (it varies depending on the pump). Also water pumps are far better at pushing water up a pipe from the bottom rather than pulling water from the top. How do we get water up from the bottom of a 50 metres deep hole?

Standard Water Pumps

For most wells and bores that are less than 5 metres deep a low cost standard water pump will do. The pump can be placed at ground level and a delivery pipe comes from the water up to the pump which sucks rather than pushes the water up the pipe. There is, however, a problem. If, when the pump stops running, the water runs back down the delivery pipe air can get into the pipe and the pump and, because air is not a solid mass (non compressible) in the way that water is, the pump will not be able to suck water. To start the pump we will need to 'prime' the pump and the delivery pipe by filling them with water. To stop the water running back down the pipe when the pump stops running we need to install a non return valve on the bottom of the delivery pipe to make sure it stays full of water.

Jet Pumps

If we have a bore or well deeper than 5 metres and less than say 20 metres a standard pump will not do, it will not be strong enough to suck the water, however a modfied version of a standard pump can be used that is capable of pumping from greater depths, probably down to around 20 metres. These are known as jet pumps. A jet pump works by forcing water down a second pipe that goes back down the well and joins into the delivery pipe down in the well. It creates a circulation of water up the delivery pipe back down the secondary pipe and bck up the delivery pipe again. This circulating water helps to push water coming up the delivery pipe. Jet pumps are also low cost and are mounted at ground level. If we have to pump water from more than 20 metres in depth we have to go to a far more specialised pump.

Submersible Pumps

Special types of water pumps have been developed for use in bores over say 20 metres deep where normal pumps simply aren’t up to the job. These pumps go at the bottom of the bore and push the water out. But just a minute, a bore is usually only 4 or 6 dims wide and the bore is full of water at the bottom.

These pumps specially designed pumps known as submersible pumps and are long cylindrical devices. At the bottom of the pump is a water proofed electric motor which drives a whole series of small circular water pumps all stacked up one on top of the other and combined in a stainless steel housing. These pumps have to be powerful and, as any diver will tell you, every 10 metres of water depth the pressure increases by 14.7 pounds per square inch. To lift water 50 metres you need a pump that can pump water at 74 pounds per square inch, to put that into perspective the air pressure in your car tyre is only around 30 pounds per square inch. A bore 130 metres deep will typically need a pump capable of pumping water at 190 pounds per square inch (6 times the pressure in your car tyre) and will need a whopping 5.5 kilowatts of electrical power. Good quality submersible pumps for an average depth bore (30 to 50 metres) are expensive.

The submersible pump will also need a pipe to carry the water to the surface and a waterproof power cable to carry electricity to the pump.

Copyright © Phil Wilson March 2013
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