What is a rain water catchment system? The experience of CREPA

Faq sheet on rainwater catchment systems, prepared by CREPA, Burkina Faso

Introduction

Mastering the techniques of water recovery is of central importance to further the development in many countries. Many specialized institutions have developed technologies in order to meet the increased water demand of populations. Rain water catchment, even though it is being used since ancient times, still ranks among these technologies.

Facing the negative effects of parameters like demography pressure, the geological nature of rocks, the bad bacteriological and physico-chemical quality of ground water in some regions, temperature increase and decrease of precipitations, have raised interest in appropriate technology research. In choosing facility or the technique one will have to consider:

• the origin of the resource (ground water, surface water or rain water)
• the social, economic and cultural factors
• other environmental factors.

The Regional Centre for low cost water and sanitation (CREPA) was set up in 1988 as a collaborative centre of WHO (World Health Organization), in order to contribute to the achievement of the international decade for water and sanitation (1981-1990). CREPA intends to promote appropriate technologies in the water and sanitation sector. With its experience, CREPA has developed or adapted many technologies that are in use in many communities nowadays.

After a successful experimentation phase two types of rain water catchment systems have been promoted by CREPA.

This document describes two types of rain water catchment systems promoted by CREPA.

Rainwater harvesting

What is a rainwater catchment system ?

A rainwater catchment system is a rainwater collection and storage system, composed of several main parts:

• a collection area: it can be a roof or any area especially arranged for this purpose
• one or more gutters made of bamboo, a galvanized metal sheet or PVC. They collect rainwater from roofs and channel it into the storage tank,
• a tank: it receives water from gutters through a pipe and stores it during a period between two rainy seasons,
• a device for first rain diversion: thanks to this device, the first rains drain out the filth accumulated on the collection area (roofs) and are not collected in the tank. The type of diversion device promoted by CREPA is of T-shaped PVC fitted with a stopper at the lower end, made of the same material. When the stopper is open, water from the gutters flows down on to the ground. But if the stopper is closed, water rises and enters the tank through the pipe connected to the upper end of the T-shaped piece of PVC,
• a tap is used to get the water out of the tank,
• a drain pipe with a stopper is installed to let out the water after cleaning the tank.

In addition to these basic elements, a filter, made of wire mesh, is required to retain solids and all sorts of rubbish present in water before it enters the tank.

Rain water catchment systems are used to collect and store water during rainy seasons in order to provide drinking water to populations during dry seasons, but other uses are not excluded.

Water catchment systems promoted by CREPA

CREPA has been promoting two types of rain water catchment systems, namely:

• a system in laterite stone and ;
• a system in ferro-cement.

The difference between the two systems resides in the fact that the tank walls of the first are built up with stones whereas those of the latter are made up with iron chicken mesh, covered by mortar cement. The building material thus obtained is called “ferro-cement”. The kind of stone varies from one site to another, but the type mostly used in Burkina Faso is laterite. In Bamako for example, granite is cheap and has been used for tank construction.

Other materials have been used for tanks. One example which can be mentioned here is that the GTZ (German Cooperation Agency) conducted an experiment using plastic film for the tank. This material disintegrates fairly easily.

Quality of water stored in a tank

The quality of rain water stored in tanks meets the World Health Organization’s (WHO) drinking water standards. This is the result of a series of studies carried out by CREPA, EIER (Ecole Inter-Etats des Ingénieur de l’Equipement Rural: interstate school for rural engineering) and ETSHER (Ecole Inter-Etats des Techniciens Superieurs d’Hydraulique et d’Equipement Rural: interstate school for hydraulics and rural engineering) in Burkina Faso (3 - 4 - 5).

Keeping this quality requires, however, a rigorous maintenance of the facility. This maintenance starts with the collection of rain water and ends with the consumption of the water stored in the tank. Basically, the maintenance consists of:

• the diversion of first rains: rain water should be allowed in the tank only when the collection area (roof) is sufficiently clean. This procedure should be repeated, during the rainy season, when rains are interrupted for more than a week. The diversion device should be easy to handle
• before using the water stored in the tank, disinfection with chlorine is advisable in order to protect the water from any contamination
• at the beginning of the rainy season, the gutters of the catchment system should be cleaned. The inside of the tank should be cleaned with water and then disinfected with chlorine. The bottom of the tank should be kept wet (with a water layer of about 5 cm) to avoid cracks..

Water collected and stored under these conditions can be used as drinking water. For instance, in a school of 300 pupils, a tank of 20 m3 can provide drinking water for more than a month, if we consider a usage per capita of 2 to 3 l/c.d at school. This is a water supply alternative in an area where potable water is scarce.

Construction cost of a CREPA type of water catchment system

Cost of water catchment systems with a tank in stone in the year 2000 (a volume of 20m3) (7)

Cost of water catchment systems with a tank in ferro-cement in the year 2000 (a volume of 20m3) (7)

* 1 Euro = 655, 597 FCFA

The costs of the materials mentioned are those of the year 2000, in Burkina Faso, when the price of cement was 90 000 FCFA and the cost of sand and gravel amounted to 6000 to 7000 F CFA/m3. The costs are indicative and can vary from one country to another according to the building material costs and living expenses (7).

Advantages of rainwater catchment systems for drinking water

The use of the rainwater catchment systems for drinking water supply offers many advantages (9):

• They are practical: supply and consumption are on the same site;
• Easy to maintain: given that the use and the maintenance of catchment systems on the roofs are fully controlled by the users of the tank;
• Cheap during exploitation: almost no spare parts and no energy required;
• Better quality of water: the quality is far higher than that of non-improved traditional sources of water, provided that the water is collected under the required conditions;
• Low environmental negative impact: rainwater is a renewable resource and its exploitation does not cause any harm to the environment, nor to future sources of water;
• Permanent supply: collection of rainwater represents always an alternative solution for water supply where it rains;
• Simple to construct: the construction of the tank is simple and local masons can be trained for the construction, making it cost reductive;
• Flexible technology: the construction of the systems can be adapted to any need.

Disadvantages of the systems

Beside the numerous advantages, the system presents some disadvantages (9):

• Construction cost is relatively important
• Supply is limited by the capacity of the tank
• Disinfection is required at the beginning of the rainy season and at any time bacteriological contamination is observed.

Some examples of systems set up by CREPA

Since its experimentation phase, many systems have been realized by CREPA. Burkina Faso, the hosting country of the CREPA headquarter is the experimentation site of this phase.

In the villages of Roumtenga and Obri-yaoghin, located respectively at 15 and 30km to the north of Ouagadougou, the capital, were the first beneficiaries. Roumtenga village hosts a system with four tanks in ferro-cement, whereas Oubri-yaoghin has four tanks in laterite stone.

In Ouagadougou town, some houses in peri-urban areas (Sector 28, Patte d’oie) have also benefited from these types of rainwater catchment systems (3). But the limited space of the plots has not helped the promotion of this technology in houses. However, water supply systems in many schools in Burkina Faso and other countries in the sub-region are based on this technology.

References

[1] Ossete J.P. (1989). La collecte et le stockage des eaux de pluie sur les plateaux Batékés : analyse technique et économique - (Catchment and storage of rain water on Batékés plateau, a technical and economic analysis.)- Brazaville, Congo : Direction de l'Hydraulique; MME, 77 p. - 24 ref.

This report on collection and storage of rainwater on « Batékés » plateau, in Congo, Brazaville, gives information on technical and economic data of tanks and rainwater catchment systems. A comparative study of tanks in ferro-cement and the GTZ type of tanks has helped to conclude that the former is more expensive than the latter. However, lessons learnt from the study show that research needs to be directed towards the selection of rainwater collection and storage techniques. This research should be focused on the means to reduce the cost of construction.

[2] Sylla D. (1993). Initiation aux technologies appropriées d ' approvisionnement en eau potable et d ' assainissement dans les pays en voie de développement : cas du Burkina Faso : rapport de stage intégré long du 12 juillet au 04 décembre 1993 au CREPA à Ouagadougou, Burkina Faso - (Introduction to appropriate water supply and sanitation technologies in developing countries : a case in Burkina Faso ( training report)).- Ouagadougou, Burkina Faso : CREPA,.- 62 p. - 7 ref.

This report describes the activities of Mr Drissa Sylla during his training period in CREPA in Ouagadougou, Burkina Faso. The trainee has focused on three main centres of interest. The first concerns the initiation of a solid waste management pilot project in an area of Ouagadougou. The second focuses on the qualitative analyses of rainwater collected and stored in ferro-cement tanks from the roofs. Finally, the third concerns the construction of improved latrines.

[3] Dakoure D. (1990). Les impluviums : vérification de certains paramètres de conception des citernes, analyse de la qualité des eaux de pluie captées avant leur introduction dans les citernes, suivi de la qualité physico-chimique des eaux des citernes de Roumtenga et Patte-d ' Oie (rapport de stage) - (Rain water catchment systems: verification of tank design parameters, analysis of water quality prior to storage in tanks, monitoring of the physico-chemical quality of water in tanks in the village of Roumtenga and in Ouagadougou.)Ouagadougou, Burkina Faso : CREPA. 44 p. - 5 ref.

In the context of promotion and development of low cost technologies in the water and sanitation sector, several rainwater catchment systems have been tested in a school in a suburb of Ouagadougou and in about six houses throughout the town. Since their construction, parameters used for the design of the tanks have been studied, together with the physico-chemical quality of the water in the tanks. At the end of the study, it was concluded that the quality of the water collected and stored in the tanks is acceptable if we compare it to other systems like wells and boreholes.

[4] Cisse B. (1991). Déferrisation des eaux de forages et suivi des impluviums (rapport de stage) - ( The removal of iron from borehole water and the monitoring of rain water catchment systems (training report).) Ouagadougou, Burkina Faso : CREPA; EIER, 43 p. - 4 ref.

This report is the outcome of research carried out by CREPA in the area of water resources recovery and water treatment. The first part deals with the removal of iron from water which is a process of removing iron content from boreholes. The second part focuses on rainwater catchment systems. The quality of water stored in tanks was also studied. It is found that the run-off water coefficient, on roofs, is 62%. The quality of water meets the WHO standard for drinking water.

[5] Agbezudo K. (1990). Contribution à l ' étude de faisabilité technique des impluviums et à l ' étude comparée de l ' évolution de la qualité des eaux de pluie, des eaux de ville (ONEA-Ouaga) recueillies dans des citernes en ferro-ciment et des eaux de forage sur le site de Roumtenga

(Contribution to a technical feasibility study of rain water catchment systems and to a comparative study of rain water quality and piped water stored in ferro-cement tanks and boreholes in the village of Roumtenga .) - Ouagadougou, Burkina Faso : EIER, 55 p. - 17 ref. -

Faced with the problems encountered in the water supply of rural, peri-urban, and even urban populations, rainwater catchment systems with ferro-cement tanks represent an alternative solution. After studying the micro-biological and physico-chemical analysis of rainwater, piped water and water from boreholes, the author concludes that the collection of rainwater is a technique that deserves to be encouraged. However, particular attention needs to be given to the quality of water stored in tanks in order to respond efficiently to the populations’ needs both quantitatively and qualitatively.

[6] CREPA/Centre Régional pour l’Eau Potable et L'Assainissement à faible coût/OUAGADOUGOU/BF. (1996). Fiches techniques des ouvrages d ' approvisionnement en eau potable et d ' assainissement (AEPA) - (Specification sheets on water supply and sanitation facilities.) Ouagadougou, Burkina Faso : CREPA, 84 p. - ill., tabl.

CREPA intends to create and promote appropriate water technologies adapted to socio-economic and cultural conditions of the country members within the water group. CREPA has successfully realized facilities like ventilated pit latrines, rainwater catchment systems, hand washing devices, and many other technologies all over Burkina Faso. This hand book is a compilation of specification sheets on technologies that convey adequate and precise information on facilitating construction and promotion of those technologies that have proved to be successful.

[7] CREPA/Centre Régional pour l’Eau Potable et L'Assainissement à faible coût OUAGADOUGOU/BF. (1997). Construction de citerne de captage des eaux de pluie (Impluvium): manuel de formation des ouvriers maçons - (Construction of rain water catchment systems : a mason’s training brochure.) Ouagadougou, Burkina Faso: CREPA, 37 p. - ill., 1 tabl.

This is a technical brochure CREPA is offering to technicians, practitioners, masons, Non-Governmental Organizations of African regions, faced with water supply related problems. It is a guide for the construction of tanks in stone. It also gives detailed information on the required building materials, design data of the collection area, etc.

[8] Alimentation en eau potable : captage de l ' eau - ( Water supply : water catchment ) OIEau/CREPA [web site] :

http://www.oieau.fr/ReFEA/module3.html#pluie, http://www.oieau.fr/ReFEA/fiches/CapteEauPluie/citerne_generalite.PDF, http://www.oieau.fr/ReFEA/fiches/CapteEauPluie/1impluviums.PDF

This site gives general information and details on construction techniques of rainwater catchment systems. The information is in French. You will find sections on: questions and anwers, knowledge tests, references and other low cost technologies.

[9] CREPA/ Centre Régional pour l’Eau Potable et L'Assainissement à faible coût/OUAGADOUGOU/BF. (1990). Séminaire national de sensibilisation et de formation des formateurs dans les technologies d ' approvisionnement en eau potable et d ' assainissement à faible coût - (National awareness raising and training seminar for trainers on low cost water supply and sanitation technologies .)Nouaktchott, Mauritania : CREPA, 35 p.

The document is a report of a national workshop organized in Nouakchott from 5th to 8th March 1990 on raising awareness for appropriate technologies in the low cost water and sanitation sector, by CREPA.

Contact persons

• Cheick Tidiane TANDIA, General Director of CREPA, 03 BP 7112 Ouagadougou, Burkina Faso 03 Tél.: 00 226 36 62 10 or 36 62 11 Fax : 00 226 36 62 08
• Cyrille Amégnran, Engineer, 03 BP 7112 Ouagadougou, Burkina Faso 03 Tél.: 00 226 36 62 10 or 36 62 11 Fax : 00 226 36 62 08

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Date written: 12 Mar 2004

Date revised: 7 Jun 2004

Author: Cheick Tidiane TANDIA, General Director

Organisation: Centre Régional pour l'Eau Potable et l'Assainissement à faible coût (CREPA), Burkina Faso

Reviewed by: Trea Christoffers, Programme Officer, IRC

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