Building Serv. Eng. Res. Technol. 27,2 (2006) pp. 75 /83
Modern engineering interventions to reduce the transmission of diseases caused by inadequate domestic water supplies and sanitation in developing countries DD Mara, PhD DSc(Eng) FICE FIBiol FCIWEM School of Civil Engineering, University of Leeds, Leeds, UK
Inadequate water supplies and inadequate sanitation are responsible for a large proportion of disease transmission in rural and periurban areas in developing countries. Engineering interventions for water supply and sanitation improvements in rural areas are well understood, but not to the same extent in periurban areas. Greater innovation is required to provide poor and very poor periurban households with adequate and affordable water supplies and sanitation. Periurban water supplies can be developed on the large scale required through standpipe co-operatives and yard-tap supplies in conjunction with a sensible tariff structure. Periurban sanitation is only likely to be feasible with the largescale adoption of simplified (condominial) sewerage in conjunction with innovative sanitation service delivery mechanisms.
1 Introduction At the end of 2003 some 1.2 billion people lacked an adequate water supply and 2.6 billion were without adequate sanitation.1 Almost all these people live in developing countries and the effects of inadequate water supplies and sanitation on their health is huge: in 2000 they were responsible for 4% of all deaths in the world and for 5.7% of the global burden of disease.2 The diseases related to inadequate water supplies, inadequate sanitation, and inadequate personal and domestic hygiene (collectively termed water- and excreta-related diseases) are listed in Table 1.3 Diarrhoeal disease, regarded in industrialized countries as more of a nuisance than a serious disease, kills over a million children under the age of five in developing countries, and Address for correspondence: DD Mara, School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK. E-mail:
[email protected] # The Chartered Institution of Building Services Engineers 2006
its incidence in both industrialized and developing countries is very high, especially in children under the age of five (Table 2).4 Associated with chronic infections of many of these diseases are common cancers, such as colorectal, penile and bile duct cancers and Burkitt’s lymphoma.5 The global economic costs are correspondingly huge: in 1979 (the latest year for which data are available) it was estimated that 360 400 billion working days were lost in developing countries as a result of water- and excreta-related diseases; valuing each day lost at US$0.50 gives a cost of US$180 200 billions, equal to 50% of the GNP of all developing countries in that year, so that the actual output of developing countries was around one third below their potential output.6 The United Nations designated the 1980s as the ‘International Drinking Water Supply and Sanitation Decade’ and the 1990s as ‘Safe Water 2000’, and the current target in the Millennium Development Goals is to halve /
/
/
10.1191/0143624406bt148oa
Non-latent No intermediate host High infectivity Medium to high persistence Unable to multiply Latent Very persistent Unable to multiply No intermediate host Very high infectivity Latent Persistent Able to multiply Very high infectivity Cow or pig intermediate host
B. Non-faeco-oral water-washed diseases
C. Geohelminthiases
D. Taeniases
Improve water quantity, availability, and reliability (water washed disease control); improve water quality (waterborne disease control); hygiene education
Control strategies
Beef and pork tapeworm infections
Ascariasis; trichuriasis; hookworm infection
As C above, plus proper cooking of meat and improved meat inspection
Sanitation; effective treatment of excreta or waste-water prior to reuse; hygiene education
Skin infections (scabies, leprosy, yaws) Improve water quantity, availability and Eye infections (trachoma, conjunctivitis, reliability; hygiene education including that caused by Encephalitozoon hellem) Louse-borne fevers
Viral: Non-latent (except Ascaris) No intermediate host Hepatitis A, E and F Infectivity: medium to low Poliomyelitis (bacteria), high (others) Rotaviral diarrhoea Persistence: medium to high Adenoviral diarrhoea (bacteria) low to medium (others, Noroviral diarrhoea Bacterial: except Ascaris: very high) Able (bacteria) and unable Campylobacteriosis (others) to multiply outside host Cholera Helicobacter pylori infection Pathogenic Escherichia coli infection Salmonellosis Typhoid and paratyphoid Yersiniosis Protozoan: Amoebiasis Cryptosporidiosis Cyclospora cayetanensis diarrhoea Enterocytozoon bienusi diarrhoea Giardiasis Isopora belli diarrhoea Helminthic: Ascariasis Enterobiasis Hymenolepiasis
A. Faeco /oral waterborne and water-washed diseases
Examples
Environmental transmission features
Category
Table 1 Unitary environmental classification of water- and excreta-related diseases3
76 Reducing disease transmission
Decrease passage through breeding sites; destroy breeding sites; larvicide application; biological control; use of mosquito netting and impregnated bed nets Improve storm-water drainage; public education
Rodent control; hygiene education; decreased contact with contaminated water; public education
Water-related: Malaria Dengue Rift Valley fever Japanese encephalitis Yellow fever African sleeping sickness Onchocerciasis Excreta-related: Fly-borne and cockroach-borne excreted infectionsa Bancroftian filariasis Rodent-borne excreted infectionsa Leptospirosis Tularaemia
F. Insect-vector diseases
G. Rodent-vector diseases
Excreted infections comprise all diseases in Categories A, C and D and the helminthic diseases in Category E.
a
Decrease contact with contaminated water; improve domestic plumbing; public education Decrease contact with contaminated waters; sanitation; treatment of excreta or wastewater prior to reuse; public education Drying of flood-damaged homes; public education
Bacterial: Leptospirosis Tularaemia Legionellosis Helminthic: Schistosomiasis Clonorchiasis Fasciolopsiasis Guinea worm infection Fungal: Pulmonary haemorrhage due to Stachybotrys atra infection
Latent Persistent Able to multiply High infectivity Intermediate aquatic host(s)
E. Water-based diseases
Control strategies
Examples
Environmental transmission features
Category
Table 1 (Continued)
DD Mara 77
78 Reducing disease transmission Table 2 Diarrhoeal disease (DD) incidence per person per year in 2000 by region and age5 Region
DD incidence All ages
DD incidence 0 /4 years
DD incidence 5 /80/ years
Industrialized countries Developing countries World average
0.2 0.8 /1.3 0.7
0.2 /1.7 2.4 /5.2 3.7
0.1 /0.2 0.4 /0.6 0.4
the number of people with inadequate water supplies and sanitation in 1990 (the base year) by the end of 2015.7 The World Health Organization and UNICEF have a goal of ‘water and sanitation for all’ (which was also the goal of the 1980s and 1990s) by the end of 2025.8 This last goal means that around 300 000 people will need to receive adequate water supplies and around 500 000 ( 50% in rural areas 50% in so-called urban, but actually periurban, areas) will need to receive adequate sanitation every day during 2001 2025. The water goal should be achievable ( 370 000 people were served per day in the 1980s), but the sanitation goal requires a vast effort (only 200 000 people were served per day in the 1980s and 1990s). Despite the magnitude of the effort required to achieve the sanitation goal, and despite many sector professionals privately admitting that it is essentially impossible to achieve it by the end of 2015 (even by the end of 2025), the world should nevertheless aspire to its achievement. If it does not, it will then have to contend with a global population of 9 billions in 2050, with almost all growth occurring in urban (ie, periurban) areas of developing countries,9 and the number of people to be served to meet a sanitation target by the end of 2050 will be even greater and more daunting from both a technological perspective and an economic one. /
logically complex* less so with water than with sanitation, but even getting people to wash their hands regularly is difficult, so hygiene education is a vital part of rural water supply and sanitation programmes. The webpages of WaterAid (a UK charity for water supply and sanitation in poor communities in Africa and Asia) should be consulted for further details.10 /
/
/
/
/
/
2 Rural areas Water supplies and sanitation systems for rural areas are technically simple (for example, handpumps and improved latrines), but socio-
3 Periurban areas In high-density low-income periurban areas, where most of the global population growth in the next few decades will occur and where morbidity and mortality are higher than in rural areas, the principal engineering challenge is to develop and implement affordable solutions for improved water supplies and sanitation. Hygiene education is also very important, but sociological aspects are more straightforward than in rural areas as periurban residents are forced, by the high population densities of their neighbourhoods, to face the daily reality of the effects of inadequate sanitation* ill health and highly visible human excreta. /
3.1 Water supplies The challenge here is to extend the urban reticulation system from middle- and highincome areas to periurban areas and design a tariff structure that is affordable by poor and very poor households. One three-part solution is to: a) provide free standpipes (public taps) in very poor areas; b) develop a network of ‘standpipe co-operatives’ in poor areas (one standpipe for a group of 5 25 households); /
DD Mara and (c) provide ‘yard tap’ supplies (one tap per household) in poor areas that are able to pay for them. None of these supplies would be metered. Standpipe co-operatives pay a monthly tariff equal to the number of households in the co-operative multiplied by a small proportion (eg, 1%) of the local minimum wage. The co-operative as a whole is responsible for the monthly payments; it collects money from each of its members and pays the total amount to the water supply authority. Yard tap supplies are paid for by each household individually; the tariff is a higher proportion of the local minimum wage (eg, 5%); this is the charging system used throughout Brazil, for example. Provided non-poor households (which use most of the water, often to the extent that there is insufficient left for poor and very poor households) pay a financially realistic tariff for their water consumption (such as an increasing linear tariff), the financial viability of the water supply authority is ensured.11 3.2 Sanitation There are several options for affordable sanitation: on-site systems such as improved latrines or pour-flush toilets12,13 off-site simplified sewerage,14 and ecological sanitation which can be either on-site or off-site.15 The choice between these options depends on population densities, costs and, in the case of ecological sanitation, on whether the householders are willing and able to reuse (either individually or communally) their household excreta and grey water. Cost is the most important criterion. Data from South Africa (Table 3)16 indicate that residents of highdensity periurban areas would opt for simplified sewerage, a low-cost system developed in northeast Brazil in the early 1980s where it was found to be around 20% of the cost of conventional sewerage, with monthly charges of US$ 1.50 per household.14 Simplified sewerage (also known as condominial sewerage) is designed using the same /
79
Table 3 Construction costs of sanitation technologies in South Africa16 Sanitation technology
Construction costa
Single-pit VIP latrine Single-pit PF toilet Ecological sanitation toilet Simplified sewerage Conventional sewerage
600 /3000 2000 /3000 3000 /4000 2500 /3000 7000 /8500
a ZAR, 2002 (exchange rates: ZAR 1000/US$ 87/EUR 100).
basic hydraulic design procedure as used for conventional sewerage but without any of the extremely conservative factors of safety that have accrued with the latter over the last 150 years or so. For example, the wastewater flow peak factor is 1.8 (rather than 3); a wide range of proportional depth is used (0.25d/D 50.8, where d is the depth of flow and D the sewer diameter); the minimum peak flow is taken as 1.5 l/s per household (approximately the flow induced by a single toilet flush); and a minimum tractive tension of 1 kN/m2 is used as the self-cleansing criterion (rather than a minimum velocity of flow of 0.6 m/s). The minimum sewer diameter is 100 mm, for which the value of the minimum gradient is calculated as 1 in 214 (a value of 1 in 200 is generally used). The minimum gradient is based on the peak flow at the start of the project, and the sewer diameter on its value at the end of the project (in Brazil the ratio of final to initial peak flows is often 5, so this design basis is important in ensuring the sewer has sufficient hydraulic capacity throughout its design life). The primary sewers are laid within the housing block (Figure 1), rather than in the street, and this is responsible for much of the cost savings. Simple junction boxes and inspection chambers are used in place of manholes (Figure 2), and this is also a major contributor to cost reduction. In Natal, the capital of the northeastern state of Rio Grande do Norte, the capital cost per household was US$ 325 in the mid-1980s (compared with around US$ 1500 /
/
/
/
80 Reducing disease transmission
Figure 1 Typical in-block layouts for simplified sewerage (left, existing unplanned areas; right, new housing estates)
for conventional sewerage). Simplified sewerage was found to be cheaper in Natal than onsite sanitation systems (such as pour-flush
toilets) at population densities above the quite low density of 160 people per ha.14 Sewers designed in this way have been operating without major problems in Brazil for over 20 years.17 Simplified sewerage has been so successful in periurban areas that CAESB, the water and sewerage company for Brası´lia and the Federal District, now uses it in high-income areas of the city, as well as in low-income areas (Figures 3 and 4). Current costs for simplified sewerage in Brası´lia are US$ 40 60 per person (ie, US$ 200 300 per household for a typical Brazilian household size of five).18 Operation and maintenance procedures vary between the state water and sewerage companies in Brazil: some subcontract O&M to local engineering companies who place a technician engineer and 2 3 labourers in each neighbourhood served by the system; others (for example, CAESB) undertake it themselves (Figure 5). Simplified sewerage is now used in several other countries (eg, Bolivia,19 India,20 Pakistan21 and Sri Lanka22). It has been particularly successful in India, where it is generally known as ‘slum networking’.23 There is /
/
/
/
Figure 2 Simple junction boxes (here made from larger diameter concrete sewers; brick boxes are a common alternative)
DD Mara
Figure 3 Installation of simplified sewerage in Lago Sul, a high-income district in Brası´lia
usually some initial opposition from conservative engineers familiar only with conventional sewerage, who find it difficult to believe that a 100-mm diameter sewer laid at a gra-
81
Figure 5 A water-jet pump (mounted in a commercial van) used to clear blockages in small-diameter sewers in Brası´lia
dient of 1 in 200 can operate without rapidly becoming blocked, but this opposition generally disappears when a demonstration project is built. Local sewerage design codes and building regulations may need to be amended to ‘legalize’ simplified sewerage (this was done in Brazil,14 for example). 3.3 Sanitation for all in periurban areas? Is the Millennium Development Goal for sanitation feasible in periurban areas? It requires 250 000 people to receive improved sanitation per day during 2001 2015. Simplified sewerage is likely to be the only sanitation option that has any chance of providing improved sanitation to this huge number of people, if only because it is a sewerage technology and thus can be more readily accepted by sewerage engineers working in either public or private sector organizations* they are certainly very reluctant to have anything to do with on-site sanitation technologies. If global society, national governments and local councils are really serious about meeting the sanitation goal and thus, and more importantly, achieving a real improvement in periurban health (and thus to urban health), major changes are needed. Not only has simplified sewerage to be adopted on a truly Herculean scale (periurban areas are /
/
/
Figure 4 Prefabricated plastic sewer junction box used in Brası´lia and other Brazilian cities
82 Reducing disease transmission the modern Augean stables), but there has to be a fundamental shift in policy to enable innovative service delivery mechanisms (including, for example, land tenure reform, public private partnerships in which periurban communities are actively involved, sensible tariff structures, and so on).24 /
4 Conclusions 1) Inadequate water supplies and inadequate sanitation in rural and periurban areas in developing countries are responsible for a large proportion of global disease. 2) Innovative water supply delivery systems are required in periurban areas, such as standpipe co-operatives, with sensible tariff structures so that poor and very poor households are able to have an adequate and affordable water supply. 3) Simplified sewerage has to be adopted on a very large scale to provide the periurban poor with improved sanitation. Innovative sanitation service delivery mechanisms are also necessary.
References 1 UNICEF, WHO. Meeting the water and sanitation MDG target: a mid-term assessment of progress. Geneva: World Health Organization, 2004. 2 Pru¨ss A, Kay D, Fewtrell L, Bartram J. Estimating the burden of disease from water, sanitation, and hygiene at a global level. Environmental Health Perspectives 2002; 110: 537 /42. 3 Mara DD, Feachem RGF. Water- and excreta-related diseases: unitary environmental classification. J. Env. Eng., Proceedings of the American Society of Civil Engineers 1999; 125: 334 /39. 4 Mara DD, Clapham D. Water-related carcinomas: environmental classification. J. Env. Eng., Proceedings of the American Society of Civil Engineers 1997; 123: 416/22.
5 Mathers CD, Stein C, Ma Fat D, Rao C, Inoue M, Tomijima N, Bernard C, Lopez AD, Murray CJL. Global burden of disease 2000: Version 2, Methods and results. Geneva: World Health Organization, 2002. 6 Pearce DW, Warford JJ. World without end: economics, environment, and sustainable development . Oxford University Press, 1993. 7 UN Task Force on Water and Sanitation. Health, dignity, and development: what will it take? Earthscan Publications, 2005. 8 WHO, UNICEF. Global water supply and sanitation assessment 2000 report. Geneva: World Health Organization, 2000. 9 World Bank. Responsible growth for the new millennium: integrating society, ecology, and the economy. Washington DC: The World Bank, 2004. 10 www.wateraid.org.uk. 11 Mara DD. Rational water tariffs for poor and non-poor consumers in developing countries. Paper presented at the IWA International Conference on Water Economics, Statistics and Finance, Rethymno, Crete, 8/10 July 2000. 12 Mara DD. The design of ventilated improved pit latrines (TAG Technical Note No. 13). Washington, DC: The World Bank, 1985. 13 Mara DD. The design of pour-flush latrines (TAG Technical Note No. 15). Washington, DC: The World Bank, 1985. 14 Mara DD, Sleigh PA. Tayler K. PC-based simplified sewer design . Leeds: School of Civil Engineering, University of Leeds, 2001. 15 Winblad U, Simpson-He´bert M. Ecological sanitation , 2nd ed. Stockholm: Stockholm Environment Institute, 2004. 16 Department of Water Affairs and Forestry. Sanitation for a healthy nation: sanitation technology options. DWAF, Pretoria, 2002. 17 Sarmento, VBA. Low-cost Sanitation improvements in poor communities: conditions for physical sustainability. PhD thesis. Leeds: University of Leeds, 2001. 18 McCann B. The sanity of ecosan. Water21 28/29 April 2005. 19 Water and Sanitation Program. El Alto Condominial sewerage pilot project impact assessment: a summary. WSP Andean Region, Lima, 2001. 20 Water and Sanitation Program. Ahmedabad parivartan. WSP South Asia, New Delhi, 1997.
DD Mara 21 Sinnatamby GS, McGarry MG, Mara DD. Sewerage: shallow systems offer hope to slums. World Water 1985; 9: 39/41. 22 Corea EJH. Appropriate disposal of sewage in urban and suburban Sri Lanka . PhD thesis. Leeds: University of Leeds, 2001. 23 Parikh H, Surkar D, Zanders MO. Sustainable infrastructure development for slums and
83
villages. In Proceedings of the 28th WEDC Conference ‘Sustainable environmental sanitation and water services’ in Reed B, editor, WEDC, University of Loughborough, 2003. 24 Hasan A, Patel S, Satterhwaite D. How to meet the Millennium Development Goals (MDGs) in urban areas. Environment & Urbanization 2005; 17: 3 /19.
