TECHNICAL PAPER # 68
By William Ashe
P. Alen Pashkevich
Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 * Fax:
Understanding Water Wells
Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
technologies of intrest to people in developing countries.
The papers are intended to be used as guidelines to help
people chooe technologies that are suitable to their
They are not intended to provide construction or
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteer technical experts on a
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Patrice Matthews
handling typesetting and layout, and Margaret Crouch as
The author of the paper William Ashe, is the Director of
Ashe has experience in drip irrigation,
wind mills and jet pumps. He has travelled in Haiti,
Republic and Kenya.
The six reviewers who are all VITA Volunteers were, Douglas
Denatale who is employed by Whitman & Howard, Inc. and
in geology, Joseph Gitta, self-employed in Beekeeping,
William Lorah, a civil engineer with Wright Water Engineers,
Robert Moran, a consultant in geology, P. Alan Pashkevich an
engineer in Georgia Tech Research Institute, and Don C.
an engineer for the city of Portland.
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries.
offers information and assistance aimed at helping
and groups to select and implement technologies appropriate
VITA maintains an international Inquiry Service,
a specialized documentation center, and a computerized
roster of volunteer technical consultants; manages long-term
field projects; and published a variety of technical manuals
UNDERSTANDING WATER WELLS
VITA Volunteer William A. Ashe
Safe drinking water is a basic human need.
Yet, according to the
World Bank, water-borne diseases are the leading cause of
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
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
people have made wells of many types, shapes, and sizes,
variety of tools.
Such wells are usually not the best and often
prove dangerous during construction or after continued
used to supply drinking water for humans are often
sealed at the surface and thus allow contaminated surface
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
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
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
for them and whether hand-dug wells or drilled wells are
their means. Drilled
wells can be deeper, safer, and more durable
than hand-dug wells but their construction is more expensive
in many rural areas, the equipment or funds for drilling may
be available. Fortunately, simple machinery has been
that can be used if money or expertise is not too scarce.
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
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.
When it rains, some of the water soaks into the ground and
trapped in porous soils.
Other water flows into and through
layers of loose or porous rock.
This is ground water.
saturated layers of rock and soil that can yield a supply of
water sufficient for wells or springs are called
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
How Wells Work
A water well is a hole that is dug, driven, or drilled
the earth, into the aquifier, to remove ground water for
use. The sides of
the hole can be left without support, but are
often supported by brick, stone, concrete, steel pipe, or
materials. Water is
removed from the well by a variety of
methods, of which the simplest is lowering and raising a
or other container.
A variety of pumps can also be used; these
may be hand operated or powered by petrol, electricity,
Most hand-dug wells are less than 30 meters deep, but deeper
wells have been successfully constructed under special
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.
the well will fill to the
level if the water table.
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.
sand it is slower.
There are basically three sections to a well:
The sanitary seal at the top,
the well casing or well support in the
the well intake or well screen at the
The top section must be finished so that it stands higher
the ground and is sealed on the outside from surface water
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
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
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).
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.
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
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
expected f rom the new well.
Samples of water f rom existing wells
can be sent to a laboratory to determine the mineral and
Contamination from surface sources must be avoided in
the proposed well site.
For example, avoid latrines, animal
stalls or barns, creeks, cemeteries, agricultural fields
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
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
HEALTH AND SAFETY DURING CONSTRUCTION
During well construction, precautions must be taken to clean
tools that have been used in other projects because they may
source of contamination.
The well should be covered after each
day's work to protect it from falling debris. Sanitary
should be provided for the construction workers, who should
warned against using the area near the well for this
Defecating or urinating in the well during or after
should be strictly prohibited.
Many risks are associated with a hand dug well, especially
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
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
under these conditions can cause fatigue and fainting.
sometimes becomes displaced by other gases or it may become
Petrol-engine exhaust and natural explosive gases from
within the earth are particularly deadly. Hence, a
system is a must when working below 10 meters.
Pipes or hoses to
carry fresh air from the surface to the diggers must be
hand operated fan or bellows can be the responsibility of
person at the surface who ensures that the ventilation
operating continuously while the diggers are working in a
deeper than 10 meters.
A further hazard arises when continuing to remove the soil
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
as the soil is brought out with the water that
is removed, a doughnut-shaped cavern will form around the
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-liter
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.
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
Whether hand or machine methods are used, digging is easiest
areas of loam, sand, or gravel and where small stones are
(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
TYPES OF WELLS AND SOIL CONDITIONS
GENERAL GUIDE OF SIZES AND CONDITIONS
FOR EACH TYPE OF DRILLING SYSTEM
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Open wells typically have diameters of 1 to 3
meters though wells larger than 4 meters in diameter are
dug. The wells may
be 10 meters deep or less, without a
supporting wall and surface supports or frame.
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
digging is completed, the temporary forms are removed and
wall is then reinforced with steel, plastic, bricks, rocks
cement casing. (Wood
or nondurable materials should be used only
for the temporary forms and not for permanent well
method is faster and less expensive than the second type,
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
the vertical walls as the well is dug so that when the water
table is reached, the reinforcement casing materials of the
and second sections are already in place.
The last portion of
the well to be completed (the water-bearing section) is dug
cased as deeply into the aquifer as possible.
of the aquifer can be achieved if water is pumped from the
during construction (Figure E).
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.
constructed by completely digging the
first section followed by digging the
second section a meter at a time.
each meter of depth cement is poured
to finish the casing before digging is
sequence is repeated
until the aquifer in reached.
water-bearing section of the well is
then completed by lowering surface-constructed
casing sections to the
bottom and allowing then to sink into
"Dig Complete and Finish Complete" is
a method used with wells that are
usually no deeper than 20 meters.
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
finished by lowering the casing (made at the surface) into
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
well. Concrete is
poured, and the forms are moved up about a
meter at a time until the well casing is complete.
of form is used at the surface, where its casing can be
without the restricted working conditions within the
well. After the
casing has cured, the forms are removed.
rods are installed and locating rings can be formed
easily by the molds.
A major disadvantage of this and the
Dig-and-Finish types is the need for a heavy framework with
strong rope and pulley assembly to safely lower the heavy
casing into the well.
To drill a well 5 to 20 meters deep in soft soils, an auger
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
hand pumps are then installed at the surface.
A percussion device can be used to drill a well 20 to 60
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
surface and cleaned each step of the way (Figure G).
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.
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
Wells can also be driven into the earth with drive points
specially designed hammers or tripod driving tools (Figure
Larger wells (10 to 50 cm in diameter) can be
drilled quite efficiently with a truck-mounted machines
efficiently using an auger, or a percussion, rotary, or air
Steel or plastic casings are lowered when the drilling is
Several kinds of earth augers (Figure J) are used in well
Each is suitable for a particular soil condition.
method involves using an engine driven pump and water power
"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
drilled and loosened soil to come up to the surf ace with
pumped water to the surface.
The pipes slowly sink into the
ground. The success of this method depends on soil
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
(Figure K). Atmospheric
pressure can force water up pipes to a
theoretical maximum of 10 meters. At greater depths,
of a suction pump is
not possible. Down-hole pumps
can be used
at any depth.
The machinery or "action" (including the piston,
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
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
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
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
Power for Pumps
If hand pumps are not used, windmills may be a good choice
lifting water from shallow or deep water wells in rural
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
Modern technology has produced solar cells that convert
directly into electricity. one of the most important
for solar cells, in rural areas all over the world, is water
companies are competing to produce solar cells
cheaply, at a cost affordable in the United States and
VII. CARE OF THE
WELL AFTER COMPLETION
Water in untapped aquifers is sealed from microorganisms and
therefore uncontaminated. Once well digging begins, the
is exposed to then and other particles in the air.
reason, after the well has been constructed, the water in it
be returned to a safe condition.
First, the completed well should be thoroughly disinfected
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 liters of chlorine
bleach into 40 liters 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
few minutes. (3)
Allow the well to stand idle overnight:
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
in advance. If
possible, a sample of water from the well (after
disinfection) should be sent to a laboratory to test its
as drinking water.
OF CHEMICALS REQUIRED FOR A
CHLORINE SOLUTION CAPABLE OF
WELLS AFTER THEIR CONSTRUCTION(*)
Bleaching Powder High
(25-354) (g) Calcium
Hypochlorite (5% Sodium
(*) This produces a chlorine concentration of approximately
This water should not be drunk by people or
The community should be informed on how to keep the water
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
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
repair and maintenance workers should enter the well.
well is put back into service after a repair, it should be
disinfected using the same method as when the well was first
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
diseases that can be acquired by simply walking through
No bucket or ropes with surface dirt should be allowed to
the well. Ropes and
buckets used to draw water from the well can
transfer contamination from hands to rope and then to the
water. In this way,
any person later drawing water from the well
can take home enough microorganisms to make the family ill
they drink it.
The need for a safe drinking water supply as expressed by
people of the community should be analyzed by workers who
responsible for deciding whether to construct the well.
projects require good leadership, planning, and execution,
but community initiative, planning, ownership, and support
essential from the start to ensure that the well is built
users want it, that the users understand how it will be paid
that the well does not adversely affect the social structure
the community, that it is used, that the well and pump are
and that water is clean when drawn and kept under sanitary
conditions by its users.
The first consideration should be for good water
considerations include cost and maintenance of the
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?
project is for several wells in a community, a number of
must be carefully resolved to arrive at the proper
the local requirements for water
the kind of wells
the workers and their pay
the type of equipment to use
the costs and materials required for
the availability of the materials
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AMOUNTS OF CHEMICALS NEEDED TO
DISINFECT A KNOWN QUANTITY OF
WATER FOR DRINKING(*)
Water Bleaching Powder
High Strength Liquid Bleach
([m.sup.3]) (25-35%) (g)
Calcium Hypochlorite (5%
(g) Hypochlorite) (ml)
(*) Approximate dose = 0.7 mg of applied chlorine per litre
permits and advance approvals by local
financing of continued
The local availability of construction materials and water
devices should be a major factor in the selection of the
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
will apply to the new well project.
Someone must be assigned to
keep records so that details of the project can be
records can often be used to resolve disputes or
ADVANTAGES AND DISADVANTAGES
VARIOUS TYPES OF WELLS AND PUMPS
to dig deep into
Easy to do
Dangerous to construct
Easy to maintain
deep in Cost more to drill
Safety in drilling Site
must be accessible
Easy to seal Needs
Good for hand pumps
Requires skilled people
Usually safer water
Slow speed Small
Simple equipment to
Usually an import item
More costly to
More skilled to repair
Needs high speed
Large equipment to
Not adaptable to
Brush, Richard E. "Wells Construction." Peace
Collection Exchange, 806 Connecticut Avenue NW, Washington,
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
St. Paul, Minnesota, 1986.
Gibson, Ulric P. and Singer, Rexford D. Small Wells Manual.
Agency for International Development, Washington, DC 20523
Koegel, R.G. Self-Help Wells.Food and Agriculture
of the United Nations, Rome, Italy, 1977.
Peace Corps Volunteers.Construction and Maintenance of Water
for International Technical Assistance Inc.,
Schenectady, New York, 1969.
Village Technology Handbook.Volunteers in Technical Assistance,
1815 North Lynn Street, Suite 200, Arlington, Virginia
Watt, S.B. and Wood, W.E. Hand Dug Wells and Their
Intermediate Technology Publications, London, England, 1979.
Apron - A slightly sloped concrete pad that surrounds the
and helps prevent contaminated surface water from finding
back into the well.
Aquifier - A water-bearing layer (stratum) of permeable
sand, or gravel.
Bit - The cutting piece at the bottom end of the tool string
loosens the soil or rock to deepen the hole.
Bottom Section - That part of-the well that extends beneath
Casing - The vertical support inside the well.
plastic, or steel pipe. Sometimes called caissons, lining.
Curb - A part of the well lining that extends out from the
and prevents it from sliding down.
Cutting Ring - A sharp-edged ring used on the bottom of a
that is being sunk into place to make sinking easier.
Drop Pipe - That section of pipe in a deep well pump
that extends between the pump cylinder from flowing back
Foot Valve - A valve at the bottom of the suction pipe that
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
Ground water accumulates in quantity in
aquifiers, from which it can be drawn out of the ground
Hydrologic Cycle - Continual natural cycle through which
moves from oceans to clouds to ground and ultimately back to
Intake Section - That part of the bottom section through
water enters the well.
Level (adjective) - Perfectly horizontal.
Level (noun) - A device used to establish a perfectly
Middle Section - That part of the well between the ground
and the water table.
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