Understanding Water Wells
By VITA Volunteer: William A. Ashe
BACKGROUND
Safe drinking water is a basic human need. Yet, according to the World Bank, water-borne diseases are the leading cause of infant mortality worldwide. These diseases are among the most serious found in the developing world. There is no single community project for development of long-term social and economic well-being, health, and comfort of a small community that is more important than a safe drinking-water supply.
Wells provide access to ground water, which is almost always safer and cleaner than surface water from lakes and rivers. Digging a well appears simple, and inexperienced and unskilled people have made wells of many types, shapes, and sizes, with a variety of tools. Such wells are usually not the best and often prove dangerous during construction or after continued use.
Those used to supply drinking water for humans are often improperly sealed at the surface and thus allow contaminated surface water to drain back into the well. Contaminated water makes people sick. Since the microorganisms (bacteria and viruses) that cause the diseases are too small to be seen, some people find it hard to believe that they are present. They often do not trace the source of their sickness to contaminated water.
This paper tells how to dig a well that provides safe drinking water for human consumption. Wells for animals and irrigation can be constructed to a much lower standard.
The paper intends to help people decide what type of well is best for them and whether hand-dug wells or drilled wells are within their means. Drilled wells can be deeper, safer, and more durable than hand-dug wells but their construction is more expensive and in many rural areas, the equipment or funds for drilling may not be available. Fortunately, simple machinery has been developed that can be used if money or expertise is not too scarce. Although this brings drilled wells within reach of some communities, they remain too costly for others. In these cases, hand-dug wells provide an alternative for producing safe drinking water.
Many good "how-to" books are available that describe in detail the construction of different types of water wells. A few are listed in the Bibliography.
PRINCIPLES
Ground Water
When it rains, some of the water soaks into the ground and is trapped in porous soils. Other water flows into and through layers of loose or porous rock. This is ground water. Water saturated layers of rock and soil that can yield a supply of water sufficient for wells or springs are called aquifers. The level of the top of the saturated layers is called the water table (Figure A). The water table may be fairly close to the surface or deep below ground. During rainy weather the water table may be higher than normal and during dry seasons it may be lower.
How Wells Work
A water well is a hole that is dug, driven, or drilled through the earth, into the aquifier, to remove ground water for human use. The sides of the hole can be left without support, but are often supported by brick, stone, concrete, steel pipe, or other materials. Water is removed from the well by a variety of methods, of which the simplest is lowering and raising a bucket or other container. A variety of pumps can also be used; these may be hand operated or powered by petrol, electricity, wind, or other means.
Most hand-dug wells are less than 30 meters deep, but deeper wells have been successfully constructed under special conditions (Figure B). Machine-drilled wells have been drilled several hundred meters deep.
When a hole, or well, is drilled or dug into an aquifer, a pool develops at the bottom of the hole. If undisturbed, the well will fill to the level if the water table. When the well is finished and in use by drawing water out, new water flows in to refill the well; this process is called recovery. The rate of recovery depends on the coarseness of the soil and the amount of gravel in the aquifer. In sand and gravel aquifers, recovery is very fast. In fine-grained sand it is slower.
There are basically three sections to a well:
o The sanitary seal at the top
o the well casing or well support in the middle, an
o the well intake or well screen at the bottom.
The top section must be finished so that it stands higher than the ground and is sealed on the outside from surface water that would otherwise drain into the well. Clay or concrete can be used to seal the well for a distance of at least five meters away from the casing. The middle section should be straight and well supported with a strong wall or casing to keep the surrounding soil from caving in.
The lowest, or water-bearing, section should extend as deeply into the aquifer as possible.
The well screen or well intake of the lowest section must allow the water to flow into the well but not admit fine soil particles (Figure C). For the water to enter the well, it is important that the well casing have many small holes. If only the bottom of the casing is open to the aquifer, only a small amount of water can be pumped. If the casing in the aquifer has many small holes (slots in steel or plastic pipe, or drilled holes in concrete) more water will be available to the well and the water is likely to be cleaner. This is true because the presence of many holes will lower the entrance velocity of the water, which thus will carry fewer particles.
Some wells are made without a casing. In sandy soil, prefabricated concrete rings, stones, or bricks can stabilize the walls. But often a concrete well casing must be made in place. Concrete for well casings should be made from a mixture of one part cement, two to three parts sand, and four to five parts gravel. To make the more porous concrete for the water bearing portion of the casing, use one part cement, one part sand, and four parts gravel. Mix in the normal way with about five gallons of water per 50 kg bag of cement.
WHERE AND WHEN TO DIG THE WELL
Avoid areas of poor water quality. Checking local maps and the closest water wells to the proposed new site can give valuable information on the quality of water that can be expected f rom the new well. Samples of water f rom existing wells can be sent to a labouratory to determine the mineral and bacterial content.
Contamination from surface sources must be avoided in selecting the proposed well site. For example, avoid latrines, animal stalls or barns, creeks, cemeteries, agricultural fields (pollution from pesticides, herbicides, etc.), and roads (fuels and coolants). The well should be constructed 50 to 100 meters from the nearest potential source of surface contamination.
The water level in a well often changes from season to season and from year to year. In dry seasons the water level will often be low. wells that have penetrated the aquifer deeply are less likely to go dry. For this reason it is best to dig the well during the dry season. Some wells penetrate more than one aquifer and are therefore more dependable for a permanent supply of water. Moreover, water from deeper aquifers is less likely to be contaminated.
HEALTH AND SAFETY DURING CONSTRUCTION
Health Measures
During well construction, precautions must be taken to clean any tools that have been used in other projects because they may be a source of contamination. The well should be covered after each day's work to protect it from falling debris. Sanitary toilets should be provided for the construction workers, who should be warned against using the area near the well for this purpose. Defecating or urinating in the well during or after construction should be strictly prohibited.
Safety Measures
Many risks are associated with a hand dug well, especially if the open type is decided upon. Understanding these risks and strictly obeying simple safety procedures will minimize the chance of an accident. The biggest risk is a massive cave-in that traps the diggers.
Other dangers arise from objects falling from the surface on top of the diggers and misunderstood instructions from the diggers below to the workers above. Without necessary vertical supports and casing rings that stand above ground level, a worker may accidentally fall into the well. The rope and pulley assembly used to lower objects into the well can fail or the bucket can be allowed to descend too rapidly. Heavy tools may cause blows to the foot or hand.
Conditions inside a well are often hot and humid, and hard labour under these conditions can cause fatigue and fainting. Fresh air sometimes becomes displaced by other gases or it may become very scarce. Petrol-engine exhaust and natural explosive gases from within the earth are particularly deadly.
Hence, a ventilation system is a must when working below 10 meters. Pipes or hoses to carry fresh air from the surface to the diggers must be used. A hand operated fan or bellows can be the responsibility of one person at the surface who ensures that the ventilation system is operating continuously while the diggers are working in a well deeper than 10 meters.
A further hazard arises when continuing to remove the soil after the water table is reached. To dig the well deeper, the water must be removed as it flows in from the surrounding aquifer, either by pumping or with buckets. The inflow carries soil with it, thus undermining the part of the well hole below the water table. Eventually, as the soil is brought out with the water that is removed, a doughnut-shaped cavern will form around the well hole. This greatly increases the danger of cave-in.
To minimize the danger, build a caisson having the same diameter as the well hole and lower it to the bottom (Figure D). It can be made of 200-litre oil drums by cutting down one side and splicing together as many as are needed to reach the needed diameter. If metal drums are not available, wood or bamboo slats overlaid with plastic sheet will do.
In this way, the migration of silt and sand into the hole will be prevented or greatly reduced, while the water is being removed to permit further digging. The caisson should be loose enough to settle down as the hole is deepened. If necessary, a second caisson can be built and placed on top of the first one.
V. WELL-DIGGINGMETHODS
Whether hand or machine methods are used, digging is easiest in areas of loam, sand, or gravel and where small stones are present (Table 1). Digging a well is very difficult in highly compacted soils, fissured (cracked) rock, and rocky terrain. It is important to select the equipment most appropriate for the soil type and terrain.
TABLE I
TYPES OF WELLS AND SOIL CONDITIONS
GENERAL GUIDE OF SIZES AND CONDITIONS FOR EACH TYPE OF DRILLING SYSTEM
| HAND DUG | HAND DRILLED | PERCUSSION | AUGER | ROTARY | AIR HAMMER | |
| Diameters | 1-20m | 10-20cm | 15-50cm | 15-50m | 15-50m | 15-50m |
| Depths | 2-40m | 10-50m | 20-500m | 20-500m | 20-500m | 20-500m |
| SOIL TYPES FOR DRILLING | ||||||
| Top Soil | yes | yes | yes | yes | yes | yes |
| Sandy loam | yes | yes | yes | yes | yes | yes |
| Clay | yes | yes | yes | yes | yes | yes |
| Silt | yes | yes | yes | yes | yes | yes |
| Sand | yes | yes | yes | yes | yes | yes |
| Sand stone | slora | no | yes | no | yes | yes |
| Lime stone | yes | no | yes | no | yes | yes |
| Gravel | yes | yes | yes | yes | yes | yes |
| Cobble stones | yes | no | no | no | no | no |
| Boulders | ? | no | no | no | no | yes |
| Dense rock | no | no | no | no | no | yes |
Hand-Dug Wells
Unsupported wells. Open wells typically have diameters of 1 to 3 meters though wells larger than 4 meters in diameter are sometimes dug. The wells may be 10 meters deep or less, without a supporting wall and surface supports or frame. Supported wells. Hand-dug wells are generally built by one of two methods.
In the first method, temporary forms are used to prevent the walls of the well from caving in as digging goes on. After digging is completed, the temporary forms are removed and the wall is then reinforced with steel, plastic, bricks, rocks or cement casing. (Wood or nondurable materials should be used only for the temporary forms and not for permanent well casing).
This method is faster and less expensive than the second type, but is more likely to cave in. It is appropriate if the well is relatively shallow and large in diameter and the soil is very compact. The second type of hand-dug well is constructed by reinforcing the vertical walls as the well is dug so that when the water table is reached, the reinforcement casing materials of the first and second sections are already in place.
The last portion of the well to be completed (the water-bearing section) is dug and cased as deeply into the aquifer as possible. Deep penetration of the aquifer can be achieved if water is pumped from the well during construction (Figure E).
Concrete-Cased Wells
Wells can also be classified according to the methods for making and installing the concrete casing sections. "Dig and Finish" wells vary in diameter from one to three meters. They are constructed by completely digging the first section followed by digging the second section a meter at a time.
At each meter of depth cement is poured to finish the casing before digging is resumed. This sequence is repeated until the aquifer in reached. The water-bearing section of the well is then completed by lowering surface-constructed casing sections to the bottom and allowing then to sink into the aquifer.
"Dig Complete and Finish Complete" is a method used with wells that are usually no deeper than 20 meters. The soil must be firm and temporarily supported to reduce the risk of cave-in. This kind of well is dug without interruption until the aquifer is reached and then is finished by lowering the casing (made at the surface) into the well from the top.
A third method is "Pour and Form." In this method forms made of metal or strong plywood are placed at the bottom of the completed well. Concrete is poured, and the forms are moved up about a meter at a time until the well casing is complete. Another type of form is used at the surface, where its casing can be constructed without the restricted working conditions within the well.
After the casing has cured, the forms are removed. Reinforcement rods are installed and locating rings can be formed easily by the moulds. A major disadvantage of this and the Dig-and-Finish types is the need for a heavy framework with a strong rope and pulley assembly to safely lower the heavy concrete casing into the well.
Hand-Drilled Wells
To drill a well 5 to 20 meters deep in soft soils, an auger is rotated at the surface by one or several workers using handles attached to it. The auger should be withdrawn from the hole at every meter or so and cleaned at the surface. When drilling is completed, a plastic or steel casing should be lowered to the bottom. Usually, hand pumps are then installed at the surface.
A percussion device can be used to drill a well 20 to 60 meters deep through more compact soils. A tripod or framework is supported vertically with a rope and pulley (Figure F).
The rope is attached to the drilling tool and in a bouncing motion should be repeatedly pulled and dropped. This will penetrate the earth deeper and deeper as the weight of drilling tool causes loosening of the soils. Sometimes tools are constructed to trap the earth inside, much like an auger, and are brought to the surface and cleaned each step of the way (Figure G). Other tools are designed to loosen the soils, with a long narrow bailing bucket to lower into the well. Water is poured into the well to form mud. The soil can then be removed with the bucket.
Machine-Drilled Wells
Small Machines. Small well drilling machines with engines are available to bore a hole in the earth. These machines are efficient, of moderate cost, and require only a few days to sink a well. Water is pumped down through the center of the drill pipe to lubricate the bit in the bottom of the well. As the drill rotates, it cuts the soil, which is flushed back to the surface with the returning water. The water-mid slurry is then be pumped back down the drill stem. When the drill pipe penetrates all of the aquifer, the well is completed as described below (Figure H).
Wells can also be driven into the earth with drive points using specially designed hammers or tripod driving tools (Figure I).
Large machines. Larger wells (10 to 50 cm in diameter) can be drilled quite efficiently with a truck-mounted machines quite efficiently using an auger, or a percussion, rotary, or air hammer. Steel or plastic casings are lowered when the drilling is complete.
Several kinds of earth augers (Figure J) are used in well drilling.
Each is suitable for a particular soil condition. Another method involves using an engine driven pump and water power to "jet" the well into the earth. In this method, water is forced down an inner pipe and through a cutting bit. The water returns to the surface through a larger pipe. Both pipes are moved back and forth to allow the cutting edge at the bottom to force the drilled and loosened soil to come up to the surf ace with the pumped water to the surface. The pipes slowly sink into the ground. The success of this method depends on soil conditions. Rocks or pebbles usually stop the process.
VI. WELL PUMPS
Suction and Down-Hole Pumps
An important decision is whether the water can be pumped by suction or whether a "down-hole" pump must be used. Suction pumps can be used in shallow" wells--those where the water tables less than 8 meters below the surface. A well with a water lifting requirement greater than 8 meters is considered a "deep" well (Figure K). Atmospheric pressure can force water up pipes to a theoretical maximum of 10 meters. At greater depths, operation of a suction pump is not possible. Down-hole pumps can be used at any depth.
The machinery or "action" (including the piston, diaphragm, and so on) of a suction pump is at the surface. The action of down-hole pumps is below the water table.
Positive-Displacement and Centrifugal Pumps
The two commonly used types of waterwell pumps for the wells described here are positive displacement (or piston) and centrifugal. Each has its limitations and advantages.
Centrifugal pumps run at higher speeds than can be obtained with hand operation. They are usually powered by petrol or diesel engines, or by electric motors. Positive displacement pumps are used for hand-pumped wells. Their cylinders can be mounted at the surface and the water can be dispensed from the well through a single pipe. In deep wells, the cylinders can be installed at the bottom of the well, from where they push the water to the surface.
They can be hand driven, powered by a submersible motor at the bottom, or driven by a shaft linked to an electric motor at the surface. Singlestage centrifugal pumps can be used at the surface to draw the water from shallow wells, but in deep wells, several stages of centrifugal pumping may be needed.
A jet pump (Figure L) is another type of centrifugal pump used at the surface for pumping water from deep wells. It circulates water down one pipe through a high-pressure nozzle and returns it to the surface through a second pipe when a small portion is drawn off for use. This system is efficient only at depths less than 15 meters.
Power for Pumps
If hand pumps are not used, windmills may be a good choice for lifting water from shallow or deep water wells in rural communities, where conventional power supplies or fuel costs are very expensive (Figure M). The initial cost of windmills is high, but they are dependable machines and last many years. When a single well is to be used as a community project, a windmill can be an excellent investment.
Modern technology has produced solar cells that convert sunlight directly into electricity. one of the most important applications for solar cells, in rural areas all over the world, is water pumping. Large companies are competing to produce solar cells cheaply, at a cost affordable in the United States and developing nations.
VII. CARE OF THE WELL AFTER COMPLETION
Water in untapped aquifers is sealed from microorganisms and is therefore uncontaminated. Once well digging begins, the aquifer is exposed to then and other particles in the air. For this reason, after the well has been constructed, the water in it must be returned to a safe condition.
First, the completed well should be thoroughly disinfected with chlorine before anyone drinks the water. Ordinary liquid household bleach (containing 5.2 percent chlorine) is commonly used. The procedure is as follows: (1) Mix two litres of chlorine bleach into 40 litres of clean water (see Table 2). (2) Pour it into the well.
If a hand pump has been installed at the surface, pump the water through it and directly back into the well for a few minutes. (3) Allow the well to stand idle overnight: or at least eight hours. (4) Pump the treated water from the well until no chemical odor is noticeable.
Verify your procedure with a local doctor or health care worker in advance. If possible, a sample of water from the well (after disinfection) should be sent to a labouratory to test its safety as drinking water.
TABLE II
AMOUNTS OF CHEMICALS REQUIRED FOR A STRONG CHLORINE SOLUTION CAPABLE OF DISINFECTING WELLS AFTER THEIR CONSTRUCTION(*)
| Water ([m.sup.3]) |
Bleaching Powder (25-354) (g) |
High Strength Calcium Hypochlorite (70%) (g) | Liquid Bleach (5% Sodium Hypochlorite) (ml) |
| 0.1 | 10 | 4.3 | 60 |
| 0.12 | 12 | 5.2 | 72 |
| 0.15 | 15 | 6.5 | 90 |
| 0.2 | 20 | 8.6 | 120 |
| 0.25 | 25 | I 11 | 150 |
| 0.3 | 30 | 13 | 180 |
| 0.4 | 40 | 17 | 240 |
| 0.5 | 50 | 22 | 300 |
| 0.6 | 60 | 26 | 360 |
| 0.7 | 70 | 30 | 420 |
| 0.8 | 80 | 34 | 480 |
| 1 | 100 | 43 | 600 |
| 1.2 | 120 | 52 | 720 |
| 1.5 | 150 | 65 | 900 |
| 2 | 200 | 86 | 1 200 |
| 2.5 | 250 | 110 | 1 500 |
| 3 | 300 | 130 | 1 800 |
| 4 | 400 | 170 | 2 400 |
| 5 | 500 | 220 | 3 000 |
| 6 | 600 | 260 | 3 600 |
| 7 | 700 | 300 | 4 200 |
| 8 | 800 | 340 | 4 800 |
| 10 | 1 000 | 430 | 6 000 |
| 12 | 1 200 | 520 | 7 200 |
| 15 | 1 500 | 650 | 9 000 |
| 20 | 2 000 | 860 | 12 000 |
| 30 | 3 000 | 1 300 | 18 000 |
| 40 | 4 000 | 1 700 | 24 000 |
| 50 | 5 000 | 2 200 | 30 000 |
| 60 | 6 000 | 2 600 | |
| 70 | 7 000 | 3 000 | |
| 80 | 8 000 | 3 400 | |
| 100 | 10 000 | 4 300 | |
| 120 | 12 000 | 5 200 | |
| 150 | 15 000 | 6 500 | |
| 200 | 20 000 | 8 600 | |
| 250 | 25 000 | 11 000 | |
| 300 | 30 000 | 13 000 | |
| 400 | 40 000 | 17 000 | |
| 500 | 50 000 | 22 000 |
(*) This produces a chlorine concentration of approximately 30 mg/l (ppm). This water should not be drunk by people or animals.
The community should be informed on how to keep the water safe to drink. Users should be trained in simple health procedures and general rules for proper water use. Boiling or chlorinating (Table 3) the water at home is often needed, in addition to basic well sanitation.
Washing or cooking should not be permitted in the immediate area of the well. Animals should be restricted from the immediate area of the well and kept at a safe distance. Only repair and maintenance workers should enter the well. Before the well is put back into service after a repair, it should be disinfected using the same method as when the well was first put into service.
No pools or stagnant water should be allowed to collect around the well surface. These pools can be breeding areas for insects as well as for microorganisms, and can spread diseases that can be acquired by simply walking through them.
No bucket or ropes with surface dirt should be allowed to enter the well. Ropes and buckets used to draw water from the well can transfer contamination from hands to rope and then to the well water. In this way, any person later drawing water from the well can take home enough microorganisms to make the family ill when they drink it.
VII. MANAGEMENT CONSIDERATIONS
The need for a safe drinking water supply as expressed by the people of the community should be analyzed by workers who are responsible for deciding whether to construct the well.
Successful projects require good leadership, planning, and execution, but community initiative, planning, ownership, and support are essential from the start to ensure that the well is built where users want it, that the users understand how it will be paid for, that the well does not adversely affect the social structure of the community, that it is used, that the well and pump are maintained, and that water is clean when drawn and kept under sanitary conditions by its users.
The first consideration should be for good water quality. Other considerations include cost and maintenance of the system. What is the total amount of money needed? Where will the construction money come from? Who will be responsible for repairing and maintaining the well and the pump through the years? If the project is for several wells in a community, a number of issues must be carefully resolved to arrive at the proper decision. For example:
o the local requirements for water
o the kind of wells
o the workers and their pay
o the type of equipment to use
o the costs and materials required for construction
o the availability of the materials
TABLE III
AMOUNTS OF CHEMICALS NEEDED TO DISINFECT A KNOWN QUANTITY OF WATER FOR DRINKING(*)
| Water ([m.sup.3]) |
Bleaching Powder (25-35%) (g) |
High Strength Calcium Hypochlorite (70%) (g) | Liquid Bleach (5% Sodium Hypochlorite) (ml) |
| 1 | 2.3 | 1 | 14 |
| 1.2 | 3 | 1.2 | 17 |
| 1.5 | 3.5 | 1.5 | 21 |
| 2 | 5 | 2 | 28 |
| 2.5 | 6 | 2.5 | 35 |
| 3 | 7 | 3 | 42 |
| 4 | 9 | 4 | 56 |
| 5 | 12 | 5 | 70 |
| 6 | 14 | 6 | 84 |
| 7 | 16 | 7 | 98 |
| 8 | 19 | 8 | 110 |
| 10 | 23 | 10 | 140 |
| 12 | 28 | 12 | 170 |
| 15 | 35 | 15 | 210 |
| 20 | 50 | 20 | 280 |
| 30 | 70 | 30 | 420 |
| 40 | 90 | 40 | 560 |
| 50 | 120 | 50 | 700 |
| 60 | 140 | 60 | 840 |
| 70 | 160 | 70 | 980 |
| 80 | 190 | 80 | 1 100 |
| 100 | 230 | 100 | 1 400 |
| 120 | 280 | 120 | 1 700 |
| 150 | 350 | 150 | 2 100 |
| 200 | 470 | 200 | 2 800 |
| 250 | 580 | 250 | 3 500 |
| 300 | 700 | 300 | 4 200 |
| 400 | 940 | 400 | 5 600 |
| 500 | 1 170 | 500 | 7 000 |
(*) Approximate dose = 0.7 mg of applied chlorine per litre of water.
o permits and advance approvals by local authorities
o financing of continued operation/repairs/maintenance
The local availability of construction materials and water lifting devices should be a major factor in the selection of the type of well to be considered (Table 4). Imported items will raise the cost considerably. Sometimes hand pumps or machine operated pumps will be part of the project. Their selection and maintenance will require people with more advanced skills.
Local authorities must be consulted on laws and regulations that will apply to the new well project. Someone must be assigned to keep records so that details of the project can be reviewed. The records can often be used to resolve disputes or misunderstandings.
TABLE IV
ADVANTAGES AND DISADVANTAGES OF VARIOUS TYPES OF WELLS AND PUMPS
| WELL TYPE | ADVANTAGES | DISADVANTAGES |
| Hand Dug | Inexpensive Easy to do Easy to maintain | Unable to dig deep into water-bearing areas. Dangerous to construct. Contaminates easily |
| Machine Dug | Gets deep in Water-bearing areas Safety in drilling Easy to seal Good for hand pumps Usually safer water | Cost more to drill. Site must be accessible Needs expensive casing Requires skilled people |
| Cylinder Pumps | Slow speed Low Cost Easily repaired Locally available Simple equipment to install | Small volumes pumped |
| Centrifugal Pumps | Efficient Quiet operation | High cost Usually an import item More costly to maintain More skilled to repair Needs high speed driver Large equipment to install Not adaptable to windmills |
BIBLIOGRAPHY
Brush, Richard E. "Wells Construction." Peace Corps Information Collection Exchange, 806 Connecticut Avenue NW, Washington, D.C. 20525. Action Pamphlet 4200.35, 1979.
Davis, S.N. and DeWiest, R.J.M.Hydrogeology. John Wiley and Sons, New York, New York, 1966.
DHV Consulting Engineers.Shallow Wells.P.O. Box 85, Amerfsoort, The Netherlands, 1979
Driscoll, F.G. Groundwater and Wells, ed.2, Johnson Division, St. Paul, Minnesota, 1986.
Gibson, Ulric P. and Singer, Rexford D. Small Wells Manual. Agency for International Development, Washington, DC 20523 USA, 1969.
Koegel, R.G. Self-Help Wells.Food and Agriculture Organization of the United Nations, Rome, Italy, 1977.
Peace Corps Volunteers.Construction and Maintenance of Water Wells. Volunteers for International Technical Assistance Inc., Schenectady, New York, 1969.
Village Technology Handbook.Volunteers in Technical Assistance, 1815 North Lynn Street, Suite 200, Arlington, Virginia 22209-8438 USA. 1988.
Watt, S.B. and Wood, W.E. Hand Dug Wells and Their Construction. Intermediate Technology Publications, London, England, 1979.
GLOSSARY
Apron - A slightly sloped concrete pad that surrounds the well and helps prevent contaminated surface water from finding its way back into the well.
Aquifier - A water-bearing layer (stratum) of permeable rock, sand, or gravel.
Bit - The cutting piece at the bottom end of the tool string that loosens the soil or rock to deepen the hole.
Bottom Section - That part of-the well that extends beneath the water table.
Casing - The vertical support inside the well. Cement cylinders, plastic, or steel pipe. Sometimes called caissons, lining.
Curb - A part of the well lining that extends out from the place and prevents it from sliding down.
Cutting Ring - A sharp-edged ring used on the bottom of a lining that is being sunk into place to make sinking easier.
Drop Pipe - That section of pipe in a deep well pump assembly that extends between the pump cylinder from flowing back into the well.
Foot Valve - A valve at the bottom of the suction pipe that prevents the water pulled up into it by the cylinder from flowing back into the well.
Ground Water - Water contained in the part of the gorund that is completely saturated. Ground water accumulates in quantity in aquifiers, from which it can be drawn out of the ground through wells.
Hydrologic Cycle - Continual natural cycle through which water moves from oceans to clouds to ground and ultimately back to the oceans.Intake Section - That part of the bottom section through which water enters the well.
Level (adjective) - Perfectly horizontal.
Level (noun) - A device used to establish a perfectly horizontal line.
Middle Section - That part of the well between the ground surface and the water table.
