The current approach to management of microbial risks
in distribution systems places a high reliance on the results
of testing indicator bacteria. There is evidence of the
fundamental weaknesses of sole reliance on such approaches
as the number of samples taken represent a minute proportion
of the water supplied and studies have demonstrated
that this approach results in limited protection of consumer
health (Payment, 1991)

Charles Niwagaba (3417113)

Guy Howard (4117807)

Kalanithy Vairavamoorthy (7217075)

Sam Godfrey (7181705)

Sarah Tibatemwa (7221500)

English

Loughborough University Institutional Repository

GODFREY, HOWARD, NIWAGABA, TIBATEMWA and VAIRAVAMOORTHY9328th WEDC Conference Kolkata (Calcutta), India, 2002Improving risk assessment and management in urban water suppliesS. Godfrey, G. Howard, C. Niwagaba, S. Tibatemwa and K. Vairavamoorthy, WEDCSUSTAINABLE ENVIRONMENTAL SANITATION AND WATER SERVICESTHE CURRENT APPROACH to management of microbial risksin distribution systems places a high reliance on the resultsof testing indicator bacteria. There is evidence of thefundamental weaknesses of sole reliance on such approachesas the number of samples taken represent a minute propor-tion of the water supplied and studies have demonstratedthat this approach results in limited protection of consumerhealth (Payment, 1991).The most effective way to ensure safety of drinking wateris through adoption of quality assurance schemes thatensure that water supplies are designed, operated andmaintained properly to avoid contamination from occur-ring. A good example of such an approach is HazardAnalysis and Critical Control Points, which has been usedin the food industry (NACMACF, 1992). Shortly aftercodification of HACCP for the food industry, Havelaar(1994) proposed its application in the water industry andthese principles have been being increasingly applied towater supply safety in developed countries (Davison et al,2002).WHO, through the revision of its Guidelines for Drink-ing-Water Quality, has recently developed a risk manage-ment tool called Water Safety Plans (WSPs) built on HACCPprinciples and there is guidance currently available in draftform (Davison et al, 2002). This approach builds on manyof the traditional risk management tools used in the waterindustry, such as the multiple barrier principle and sanitaryinspection, which were the original basis for water qualitycontrol developed in the early 20th Century (Helmer et al,1999).The purpose of WSPs is to minimise risks throughidentification and management of vulnerable points withina water supply which allow hazards (both microbial andchemical) to cause contamination. The vulnerability of thesystem is defined by its potential susceptibility to knownhazards. The combination of hazard and vulnerability canbe described as a hazardous event (NHMRC, 2002). Con-trol measures must be identified that reduce the risk ofhazardous events occurring and where there are particularpoints in a water supply where control is essential, these aretermed control points. For both control measures andcontrol points, simple means of monitoring linked directlyto process control are required and thus focus on aspectssuch as chlorine residual, turbidity and sanitary inspection.Analysis of the microbial quality is retained, but as a meansof validating and verifying performance and not as aroutine tool for monitoring process compliance.Ensuring water safetyDavison et al (2002) indicate that the delivery of safedrinking water comprises five key steps as shown below:1. Water quality targets based on health concerns set onthe basis of tolerable risk;2. System assessment to determine whether the watersupply can deliver water of a quality that meets theabove targets;3. Monitoring of the steps in the supply chain which are ofparticular importance in securing water safety;4. Management plans to be taken during normal andincident conditions; including documentation and com-munication;5. A system of independent surveillance that verifies thatthe above are operating properly.The management plans developed by a water supplierbased on a thorough system assessment and using appro-priate monitoring, combined with less frequent verificationconstitute a WSP. Typically the health sector will play animportant role in steps 1 and 5, and for the latter guidanceis available for both rural and urban areas (WHO, 1997;Howard, 2002).This paper will review current field experience in devel-oping a WSP for the supply in Kampala, Uganda by aresearch team led by WEDC. This supply produces anddistributes 120,000m3 per day though 866 kilometres ofpipeline and is an example of a private-public partnershipwith all infrastructure owned by the parastatal NationalWater and Sewerage Corporation (NWSC), who also oper-ate the treatment works. The distribution system is oper-ated by a private contractor (OSUL) who have operationalresponsibility for control of the water supply and itsquality, overseen by the Water Quality Control Depart-ment (WQCD) of NWSC.Risk management steps in UgandaThe key to the implementation of WSPs is through gaininga thorough understanding of the water supply system. Todevelop this understanding, a number of stages are requiredas described below.Assembling a risk management teamTo guide the process of implementing a WSP, a RiskManagement team was assembled to work with the re-searchers from WEDC. This was a multidisciplinary team94GODFREY, HOWARD, NIWAGABA, TIBATEMWA and VAIRAVAMOORTHYcomprising of managers, engineers, water quality controlprofessionals and technicians from NWSC, OSUL and thePublic Health and Environmental Engineering laboratoryof Makerere University. The team is co-ordinated by theChief Chemist of the WQCD.Preliminary system assessmentThe next stage was to carry out a preliminary assessment ofthe system using available data on the supply and theaccumulated knowledge of the risk management team todefine the vulnerability of the system and to identify controlmeasures. One output of this preliminary assessment is aflow diagram of the system to increase the understanding ofthe system by the risk management team. Figure 1 outlinesa flow diagram indicating the primary processes of theKampala system.During this process the lay out of the primary, secondaryand tertiary pipelines were identified and marked on a map,with the location of major water system infrastructure suchas service reservoirs and primary valves identified. Thisstage also included an assessment of whether the treatmentworks was capable of providing water to ensure that waterentering the system is of adequate quality.An evaluation of the potential vulnerability of the systemto external hazards was undertaken using the flow diagramto identify components in the system likely to be at greatestrisk of failure. This involved assessing aspects such as pipematerial, pipe age, pipe length and condition and locationof service reservoirs.The hazards in the environment were also mapped ontothe system using the GIS platform to provide an overall riskmatrix including vulnerability and hazard. A risk map wasdeveloped to identify areas of particular concern. Overlainon the system risk map was an estimation of user vulner-ability (a measure of socio-economic status and serviceFigure 1. Flow diagram of Kampala systemSurface water use Abstraction of surface water TreatmentStorage Reservoir Distribution Consumerlevel) which provides an indication of the relative impor-tance of different parts of the supply.From a review of the risk map, a number of specificcontrol measures were defined that would limit contamina-tion and these covered actions at service reservoirs, valveboxes and in the tertiary infrastructure. Some of thesecontrol measures were defined as control points, as theywere specific points within the system where contamina-tion will have particular adverse effects. For instance,contamination at a principal valve will lead to much morewidespread contamination of the system than a valve in thetertiary infrastructure.Field assessmentThe initial system assessment was “ground truthed” througha field assessment. The assessment is designed to identifyinspection points with in the distribution system that willact as a surrogate for information obtained during theinitial system analysis. Inspection points were identifiedbased on the criteria outlined in table 1:Points that fulfilled the above criteria were then locatedand the position provided on maps to assist inspectors inlocating the inspection points during the system assess-ment. A total of 175 inspection points were identified in theKampala system including service reservoirs, major valvesand a randomly selected number of connections to house-holds or public taps to assess the state of tertiary infrastruc-ture. Each inspection point was located using a GPS toensure they could be accurately transferred onto the riskmap. At each inspection point a sanitary inspection wasundertaken using a standardised questionnaire developedfrom previous experience in Uganda and Ghana and areview with local staff of the characteristics of each inspec-tion point type. In addition, analysis of free chlorineTable 1. Selection criteria for inspection points1. Scale of adverse health impacts 2. Location in relation to major primary to secondary mains connection 3. Age/Material/Length of pipe 4. High pressure or low pressure 5. Evidence of leakage from existing data 6. Record of microbial contamination from existing data 7. Proximity to hazard based on surrounding population density (as a surrogate of faecal loading)  8. Proximity to sewers, road crossings, channels and location in low-lying areas 9. Proximity to vulnerable area 10. Evidence of perpetually low residual chlorine 11. Intermittence of supply GODFREY, HOWARD, NIWAGABA, TIBATEMWA and VAIRAVAMOORTHY95residual, turbidity, pH and temperature were undertakenon-site.Results from each of these points were then plotted as anoverlay to the GIS platform with each single point repre-senting an individual form of infrastructure such as aservice reservoir, valve box, air valve or tank. The data werealso analysed to review the frequency of reporting ofdifferent risk factors, as way of identifying appropriatelimits for control measure performance.Water safety planFollowing the ground truthing, a detailed water safety planwas developed for the Kampala system and an extract ofthese is shown in table 3 below. Within the WSP, for eachcontrol point in the WSP, an estimate is made of the risk asa function of the likelihood of occurrence and the degree ofimpact. In this example the health impact is selected froma range of options shown in table 2 below. The estimationof population affected depends on the hazard and thenumbers of people that would be affected.Within the distribution system generic control measures,performance limits and monitoring can be defined for valveboxes and tertiary infrastructure. Control points wereprioritised in terms of their frequency of monitoring basedon the potential impact of failure combined with an overallrisk score based on pipe age, diameter, length, hazard score,population served and socio-economic status. Primaryvalves require weekly visits and less important valvescovered by a rolling programme of inspection. The distri-bution control measures are also to  be visited on a rollingprogramme using stratified sampling of block maps.System validationThe next stage, which should be initiated in August 2002,will be to validate the WSP using a range of microbes in linewith current thinking regarding the relationship betweenindex organisms and pathogens in drinking water (Ashboltet al, 2001). These will include E.coli, faecal streptococci,aeromonas, bacteriophage and Clostria perfringens. Initialwork on validating the risk management plan showed littlecontamination and suggests that the WSP is reliable.Work is ongoing to define appropriate water qualitytargets using quantitative risk assessment approaches andthis will be used to define both target concentrations ofindex organisms and the frequency with which verificationis required. Additional work is also ongoing to developingress and propagation models for the water supply toTable 2. Impact categoriesCategory Impact Catastrophic Mortality in large population Major Mortality in small population Moderate Morbidity in large population Minor Morbidity in small population Insignificant No detectable adverse effect gain a better understanding of the system to refine the WSPand to promote more effective risk assessment.ConclusionWSPs are a management tool designed to reduce risks ofcontaminated water in domestic supplies, placing an em-phasis on system process control and effective managementactions. The project in Kampala has shown that theseapproaches can be developed for utility supplies in develop-ing countries and offer a mechanism for more cost-effectiveapproaches to water quality management.ReferencesAshbolt N J, Grabow W and Snozzi M, 2001, Indicators ofmicrobial water quality, In Fewtrell L and Bartram J(eds.), Water quality: Guidelines, standards and health –assessment of risk and risk management for water-related infectious disease, IWA Publishing, UK, pp 289-315.Davison A, Howard G, Stevens M, Callan P, Kirby R, DeereD and Bartram J, 2002, Water safety plans (draft forconsultation), World Health Organisation (WHO), Ge-neva, Switzerland.Havelaar A H, 1994, Application of HACCP to DrinkingWater Supply, Food Control 5: 145-152.Helmer R, Bartram J and Galal-Gorchev H, 1999, Regula-tion of drinking-water standards, Water Supply, 17(3/4):1-6.Howard G, 2002, Water Supply Surveillance - a referencemanual, WEDC, Loughborough University, UK.NACMCF, 1992, Hazard analysis and critical controlpoint system, National Advisory Committee on Micro-biological Criteria for Foods (NACMCF).WashingtonD.C.NHMRC, 2001, Drinking Water Guidelines, Artaman,NSW, Australia.Payment P, Richardson L, Siemiatycki J, Dewar R, EdwardesM and Franco E, 1991, A Randomised trial to evaluatethe risk of gastrointestinal disease use to consumption ofdrinking water meeting current microbiological stand-ards, American Journal of Public Health, 81(6): 703-708.WHO, 1997, Guidelines for drinking-water quality, Vol-ume 3: Surveillance and control of community watersupplies 2nd edition, WHO, Geneva, Switzerland.SAM GODFREY, Research Associate/Assistant ProgrammeManager, WEDC, Loughborough University, Loughborough,Leicestershire.GUY HOWARD, Programme Manager, WEDC.CHARLES NIWAGABA,SARAH TIBATEMWA,KALA VAIRAVAMOORTHY.96GODFREY, HOWARD, NIWAGABA, TIBATEMWA and VAIRAVAMOORTHYCritical limits Monitoring Hazard event  Cause Risk Control measure Target Action What When  Who Corrective action Verification Microbial contamination of service reservoir Birds faeces enter through vents because covers dislodged Likely/ Catastrophic Covers of vents remain in place  Vents covered  50% of vent support struts are damaged Sanitary inspection Weekly Operations staff Repair and replace damaged vents. E.coli  Faecal streptococci. Bacteriophages Sanitary inspection Microbial contamination of service reservoir Birds faeces enter through open inspection hatches Likely/ Catastrophic Inspection covers remain in place  Inspection covers locked in place Inspection covers not in place or unlocked Sanitary inspection Chlorine residual Daily Operating staff Replace inspection cover and check chlorine consumption E.coli  Faecal streptococci. Bacteriophages Sanitary inspection Ingress of contaminated water into service reservoir Shallow water ingress through holes in reservoir; inundation by surface water of reservoir roof Moderate/ Major Structural integrity and drainage Tank structure sound with no cracks; drainage channels in good condition Drainage channels blocked; visible signs of cracks develop in tank structure Sanitary inspection Monthly  Operations staff Clear drainage channels. Take tanks off-line for repairs. Flush tank and distribution before re-commissioning E.coli  Faecal streptococci. Bacteriophage Sanitary inspection   Ingress pathways develop due to root damage Water ingress is facilitated by damage by trees planted on reservoir roof or grass roots from large tussocks Likely/ Catastrophic Structural integrity of roof; control tree growth No trees on reservoir roof and no cracks in roof Signs of tree growth or  crack development Sanitary inspection Annually Operating staff Keep grass on reservoir well maintained and close cropped E.coli  Faecal streptococci. Bacteriophage Sanitary inspection   Ingress of contamination at inlet valve Inundation of inlet valve of surface water and  Moderate/ Major Good drainage in valve box; covers on valve box;  valve packing in good condition Valve boxes covered and do not have standing water or organic material in base; packing does not leak Cover out of place, signs of water or material build-up; packing shows visible signs of damage Sanitary inspection; washout drain tests Monthly  Operating staff Clean valve box and replace cover; clear washout drain; replace packing E.coli  Faecal streptococci. Bacteriophage Sanitary inspection   Annex 1. Water safety plan extract for Gun Hill service reservoir

Improving risk assessment and management in urban water supplies

Godfrey, Sam

Howard, Guy

Niwagaba, Charles

Tibatemwa, Sarah

Vairavamoorthy, K

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Improving risk assessment and management in urban water supplies

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