E16 - How to build and maintain a water tank or a
reservoir.
Dosages to use for the concrete
Table of contents
- 1) What is involved ?
- 2) Who use this means and since when ?
- 3) Why ?
- 4) Who is primarily concerned ? Places or contexts in which this method seems most (...)
- 5) What type of reservoir / water tank should be built ? What material should be used (...)
- 6) Special difficulties and precautions doses to use for the concrete
- 7) Main advantages and drawbacks
- 8) Cost
- 9) Observations and recommendations
- 10) Achievement examples
- 11) Where to obtain further information
1)
What is involved?
Present the various options open to
the use in terms of construction and servicing water tanks or reservoirs for
storing water.
2)
Who use this means and since when?
Water tanks have been seen in arid
regions or in places susceptible to a siege since Antiquity. These water tanks
could be for domestic or community use and were very frequently underground or
even arranged in natural cavities.
3)
Why?
Arid land today accounts for over
40% of the land mass and is inhabited by 2.3 billion people, which corresponds
to about one third of the world population. The impact of poverty is most
strongly felt in the arid regions.
In such a context, water tanks capable of storing a large amount of water (and mainly rainwater) help to fight water shortages and therefore reduce the impact of poverty on the populations.
In such a context, water tanks capable of storing a large amount of water (and mainly rainwater) help to fight water shortages and therefore reduce the impact of poverty on the populations.
4)
Who is primarily concerned? Places or contexts in which this method seems
most appropriate
Reservoirs and water tanks can be
used in a variety of situations.
Firstly, in areas far from water
systems but with fairly high rainfall, they can be used to recover rainwater
and manage the resource. Nevertheless, reservoirs can be used in all dry
regions where available water stocks are essential (to deal with a breakdown in
supplies, a potentially contaminated source, etc.).
In addition, water tanks can be used
in a rural environment where there is normally space to install large
storage volumes as well as in town where the large surface area of roofs is an
excellent method of recovering water. Smaller or even underground models
are necessary in town for obvious reasons of size.
Rainwater recovery tanks can prove
useful even in areas that do not have a drought problem as they can save on
mains water. The water thus recovered can easily be used for lavatories,
washing or irrigation which reduces the financial impact of water consumption
and therefore reduces poverty.
Please refer to sheet E4
Rainwater recovery.
Lastly, the water tanks and
reservoirs can also be used simply to store the water taken from any type of
source (well, river, etc.). Nearby reserves can therefore be built up
and the water can be stored in anticipation of the dry season during which the
water courses will dry up.
5)
What type of reservoir / water tank should be built?
What
material should be used?
a)
What should be the size of the reservoir?
Small reservoirs are ideal when water is abundant
(nearby water course, high rainfall, etc.) as they fill quickly but can also be
emptied and cleaned easily. For example, in north-eastern Thailand (rainfall
about 1500 mm/year), 2 m3 jars are used which yields about 40 m3 a year and
thus covers the annual drinking water requirements for one family.
Conversely, large reservoirs
are advisable when there is a shortage of water for long periods. This is the
case, for example, when there is less rainfall or it is spread over a shorter
period. Thus, in the Saloum Islands in Senegal (rainfall 380-800 mm/year), the
rainwater is stored up to six months in 15 m3 reservoirs and 30 m3 underground
water tanks are found in Ganzu Province in China (rainfall 300-400 mm/year).
The following formula can generally
be applied to calculate the ideal volume for a reservoir : Reservoir
volume = t . n . q + eT where t represents the length of the dry season, n
the number of people using the water stored in the reservoir, q the daily
consumption per person and eT the loss through evaporation during the dry
season.
b)
What is the ideal reservoir?
Lined reservoirs: no doubt the most rudimentary
method available, lined reservoirs involve digging a hole in the ground then
covering it with a waterproof liner to store water in it or collect the
rainwater. This is the most widespread storage method as it is
especially simple and inexpensive to install (about €35 for 6 m3 for example in
Uganda) and can satisfy a family’s water requirement for four days. It is
nevertheless a very rudimentary system which should be protected, mainly to
ensure water quality.
Rainwater recovered in an amphora
Thai jars and amphora : earthenware jars or amphora
contain little and are well suited to not very arid regions. Their cost is
reasonable (about €12 in some countries, more elsewhere, for example €160 for
350 litres in a store in France). They are used to store rainwater where
rainfall is high (more than 1,000 mm/year) for use as drinking water. They can
also be used as nearby reserves where the drinking water source is far away
from dwellings. When such reserves are placed near the latrines, for example,
people are encouraged to wash their hands after using the lavatories which can
help considerably to improve
hygiene and health. A tap or long-handled ladle should be provided to avoid contaminating the water when removing it from the amphora.
N.B. The reader is invited to read sheet .... on storing water for family use for more information on the good practices to be adopted in this scenario.
hygiene and health. A tap or long-handled ladle should be provided to avoid contaminating the water when removing it from the amphora.
N.B. The reader is invited to read sheet .... on storing water for family use for more information on the good practices to be adopted in this scenario.
"Pumpkin" jars : this is a variation on the
Thai jars used in Sri Lanka. These reservoirs are made of ferro-cement and
normally have 5 m3 storage capacity. They cost slightly more - about €145. In
climates with high rainfall (about 2000 mm/year) they can supply a minimum of
20 litres of water per day for fifty days, which corresponds to the needs of a
family of five approximately.
Concrete slab water tanks : this is a relatively simple
technique but requires good technical control for optimum construction. In
normal rainfall conditions (300 to 800 mm/year), a tank can be filled with 14
m3 and the stored water is far better quality than the other resources available
in arid periods (unhealthy surface water or saline water tables). Family
involvement in constructing this type of water tank makes people more
responsible for their servicing, which is relatively simple - cleaning the
inside walls once a year and repainting the outside walls. A 14 m3 tank costs
around €200.
Building a stone reservoir
Stone, masonry or wooden water tank : this technique has the
advantage of using local materials which tends to reduce manufacturing costs.
The technique also has the advantage of keeping the water cool when the outside
temperature is high. This is a not insignificant criterion to urge the
population to consume the water from the reservoir (assumed healthy) rather
than from an unimproved source.
Ferro-cement reservoir
Ferro-cement reservoirs :
This very widespread technique is used especially in Senegal where 10 to 15 m3 reservoirs can stock sufficient water to satisfy the needs of one family in drinking water (3 L per person per day) during the eight months of the dry season. Construction is solid and servicing is very simple and inexpensive. The construction costs are however fairly high - about €900 for the entire system.
This very widespread technique is used especially in Senegal where 10 to 15 m3 reservoirs can stock sufficient water to satisfy the needs of one family in drinking water (3 L per person per day) during the eight months of the dry season. Construction is solid and servicing is very simple and inexpensive. The construction costs are however fairly high - about €900 for the entire system.
6)
Special difficulties and precautions doses to use for the concrete
The reservoir water must not be
contaminated by algae, impurities, dead leaves, twigs or dead animals and
insects. The reservoir must therefore have a hermetically-sealed, opaque lid fitted
with an inspection chamber or manhole for the large reservoirs. Use the
doses indicated at the end of the sheet for concrete reservoirs as for any
engineered structure of this type.
7)
Main advantages and drawbacks
The main advantage of this technique
is that reserves can be used during the dry season and the needs of local
populations can be provided.
In addition, storing water near
dwellings helps to alleviate the work of women who are usually in charge of
fetching the water from distant sources.
The drawback is that the water
collected can be or become more or less spoiled and is therefore not fit for
consumption if adequate purification or disinfecting measures are not taken.
See on this topic Sheet E 17 Simple water treatment methods for use in the
home.
8)
Cost
The costs can vary tremendously
depending on the type of reservoir chosen, but a broad price range of €15 to
€1,000 can be considered. A wide variety of financing solutions can be
envisaged in several cases ; on this topic, please refer to the ARENE IDF
document mentioned in 11).
9)
Observations and recommendations
The reader is invited to consult the
additional sheets E15 Methods for properly transporting and storing drinking
water at home, E 17 Simple water treatment methods for use in the home, E 18
Treatment by chlorination and E 4 Rainwater recovery.
It is advisable to clean the water
tank once a year or once every three years as a minimum. For practical reasons,
the access hatch should be made of a robust, but lightweight material (metal,
for example) : do not use concrete hatches that are very difficult to
raise. A metal ladder must also be provided inside tanks, and possibly a sealed
light, for volumes greater than 10 m3 to facilitate servicing.
Wait for the dry period in the year
to service the tank so that the water level inside it is at its lowest, then
empty it and clean the walls with a stiff brush.
10)
Achievement examples
Rainwater recovery tanks in schools
Photo Caritass
Photo Caritass
Numerous examples figure in the very
well-documented brochure from Arene Ile de France and PS Eau mentioned at the
start of the next chapter and produced following a workshop and seminar
involving several NGOs including Caritas. The construction of
ferro-cement water reservoirs for drinking water during the dry season in
Senegal where the water table water has too much fluorine and chlorides (€900
for 10 m3) is described on pages 109 to 112.
:http://www.areneidf.org/medias/publ...
Caritas Burundi has built several reservoirs and rainwater recovery systems in the country’s schools.
In north-eastern Brazil, CCFD has been involved with 750 local organisations in financing a construction programme for one million rainwater recovery tanks for five million people (€360 per 16 m3 tank built of concrete slabs).
:http://www.areneidf.org/medias/publ...
Caritas Burundi has built several reservoirs and rainwater recovery systems in the country’s schools.
In north-eastern Brazil, CCFD has been involved with 750 local organisations in financing a construction programme for one million rainwater recovery tanks for five million people (€360 per 16 m3 tank built of concrete slabs).
11)
Where to obtain further information
- ARENE IDF (Regional
Environment and New Energies Agency) : illustrated brochure presenting
numerous examples of technical achievements worldwide, mainly for rainwater
recovery. The annexes include especially a series of sheets summarising the
costs, effectiveness, permanence, etc. of miscellaneous techniques of storage
and they are highly recommended.
Available on :http://www.areneidf.org/medias/publ...
Available on :http://www.areneidf.org/medias/publ...
Eautarcie site, fairly detailed document on constructing rainwater systems and more specifically water tanks (shape, dimensions, materials, concrete quality, servicing, upstream equipment, etc. available at : http://www.eautarcie.com/Eautarcie/...
- For information on more specific topics, please consult the following sites or examples :
- Concrete example of a private individual constructing a concrete water tank :
Available at : http://home.base.be/vt661357/acceui...
- Concrete example of a private individual constructing a wooden water tank :
Available at : http://www.econologie.com/forums/fa...
- Eutarcie : Internet page dealing with the quality of water stored in the reservoir (mainly rainwater) and explaining the possible reasons for yellowish water, bad smells and how to avoid these problems.
Available at : http://www.eautarcie.com/03g.html.
- Dosages to use for the concrete or mortar (to avoid major disappointments)
: http://www.ideesmaison.com/Construc...
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