Technical Notes

SDISTechnical Note # 4Materials:Bottles vs. BagsBACKGROUND INFORMATION SUMMARYREFERENCESPlastic bottles made from PET are suitable containers for SODIS application. Higher treatment efficienciescan be achieved with plastic bags due to their larger area exposed to sunlight and smaller water depth.However, handling of plastic bottles is easier and more convenient to the users.The SODIS treatment method bases on the synergeticeffect of both water temperature and UV-A radiation(wavelength: 320-400 nm). Radiation with longerwavelength (> 400 nm) does not eliminate the bacteriaefficiently enough and UV-B (280-320 nm) is onlytransmitted through special Pyrex glass and does reachthe ground level at low intensity only. PET(Polyethyleneterephtalate) shows a good UV-A transmittanceand therefore readily available PET-bottles areused for the SODIS-treatment.On the technical side, PET-bottles are not the mostefficient containers as they show a small area forsunlight exposure and have a water depth of 6-10 cm.As a consequence, the exposed area/water volumeratio is quite low which means that water is not heatenup to maximum possible temperatures and the UV-Aradiation intensitiy on the lower side of the bottle isreduced.As an alternative, bags made out of a transparent and ablack PET-sheet have been produced (SODIS-bags)with a larger area for sunlight exposure and water depthof less than 6 cm. This increases the exposed area/water volume ratio and therefore enhances the inactivationprocess.Water Temperature [°C]605550454035302520151010.0011.0012.0013.00Time14.0015.00SODIS News No. 1, February 1997, internal reportSODIS News No. 3, August 1998, internal reportAcra, A., Jurdi, M., Mu'allem, H., Karahagopian, Y., Raffoul, Z.,(1989). Water Disinfection by Solar Radiation - Assessmentand Application. Technical Study 66e. IDRC, 1989, ISBN 0-88936-555-5. [P5]16.00July-August bagJuly-August bottleMay-June bagMay-June bottleFebruary-March bagFebruary-March bottleWter temperature curves in bottles and bags. The averagetemperature difference is about 2-3 °C.Advantages of SODIS bags☺ Faster heating up and to higher temperaturescompared to the bottle☺ More efficient inactivation of bacterias and virusesthan with SODIS bottlesDisadvantages of SODIS bags☹☹☹☹☹☹The water out of SODIS plastic bags smells plasticDifficult to handle (filling and taking the water)The SODIS plastic bag is not durable (3-6 monthsonly)A container is necessary to consume the waterSODIS bags are not readily availablePlastic is a problem for the environmentAdvantages of SODIS bottles☺ It is practical as it can be used directly at the table,no need for other container.☺ Easy to handle (filling, carrying, taking the water)☺ It is more prestigious☺ The bottle is more durable. Even after severalmonths, the bottle is still in good conditionThe bottle is easy available at low cost☺Disadvantages of SODIS bottles☹☹Plastic is a problem for the environmentSeveral bottles are needed to treat the water forthe whole family.Inactivation curves of SODIS bags and bottlesFaecal Coliforms [/100ml]10000010000100010010102040BagWaterTemperature60Bottle80UV-A Dosis [Wh/m2]1006050403020100Water Temperature [°C]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 5Climatic Conditions:Solar RadiationBACKGROUND INFORMATION SUMMARYSolar radiation reaching earth is composed of UV-B, UV-A, visible and infrared light. High radiationintensities are generally available in most developing countries, especially in those around the equator. UV-A is the most important spectrum for SODIS.Solar radiation spectrumThe sun continuously radiates enormous amounts ofsolar energy at wavelengths that cover the ultraviolet,Invisible RangeFarUV-BNearUV-AvioletblueVisible Rangegreen5 315 400 425 490 575 585 650 700 14'000wavelength (nm)visible, and infrared bands. Not all of the solar radiationreceived at the periphery of the atmosphere reaches thesurfaces of the earth. This is because the earth atmosphereplays an important role in selectively controllingthe passage towards the earth’s surface of the variouscomponents of solar radiation. Radiations with shortwavelengths are selectively scattered much moreextensively than those with longer wavelengths byatmospheric gases or particles that are smaller indimension than the wavelength of a particular radiation.Most of the radiation with a range of wavelengths from200 to 300 nm is absorbed by the ozone (O 3) layer inthe upper atmosphere.Global Solar Energy DistributionSolar radiation is unevenly distributed and varies inintensity from one geographic location to anotherdepending upon the latitutde, season, and time of day.The most favourable region for SODIS lies betweenlatitudes 15°N and 35°N and embraces the regions thatare naturally endowed with the most favourable conditionsfor solar energy applications. These semi-aridregions are characterized by having the greatestamount of solar radiation, more than 90% of whichcomes as direct radiation because of the limited cloudyelloworangeredInvisible RangeInfrared1 2 3 4 5 6 7kWh/m2 (total radiation)coverage and rainfall (less than 250 mm per year andusually more than 3000 hours of sunshine per year).The second most favourable region lies between theequator and latitude 15°N. Because humidity is highand cloud cover is frequent, the proportion of scatteredradiation is quite high. There is a total of about 2500hours of sunshine per year.It is important to note that the majority of developingcountries fall within the more favourable regionsbetween latitudes 35°N and 35°S. For this reason theycan count on solar radiation as a steadfast source ofenergy that can be readily exploited cheaply by bothrural and urban households for a multitude of purposes,including solar disinfection of drinking water.UV-A is important for SODISThe inactivation rate of micro-organisms increases withdecreasing wavelength: Visible light → UV-A → UV-B →UV-C (260 nm). The maximum DNA absorbtion correspondsto the wavelength of UV-C. Comparing UV-Aradiation and with visible light for example, more thanthe double amount of light is needed when using visiblelight only for the inactivation of microorganisms.REFERENCESAcra, A., Raffoul, Z., Karahagopian, Y., (1984). Solar Disinfectionof Drinking Water and Oral Rehydration Solutions.Guidelines for Household Application in DevelopingCountries. Published for UNICEF by Illustrated PublicationsS.A.L, Beirut, Lebanon, 1984. [P4]Wegelin, M. et al. (1994). Solar water disinfection: scope of theprocess and analysis of radiation experiments. J WaterSRT-Aqua, 1994, 43, No. 3, 154-169. [P1]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 6Climatic Conditions:Seasonal Effects and Weather ChangesBACKGROUND INFORMATION SUMMARYSolar radiation intensity varies over time and geographical location. During completely overcasted daysthe UV-A radiation intensity is reduced to one third of that recorded during a cloudless day.Solar radiation received at ground level has beenhemisphere. In Beirut for example (Latitude: 56°N), ameasured at meteorological stations for many years in horizontal surface (Figure 1), the intensity reaches amost western countries. This has not been the case in peak level of some 18 W/m 2 in June and decreases tothe developing world, where the potential and need for its lowest level close to 5 W/m 2 in December. Thethe development of sunlight as an alternative source of difference between these two levels (13 W/m 2 ) isenergy are even greater.appreciable and important.Seasonal variationDaily variation (weather changes)Solar UV-A intensity shows both seasonal (because of Figure 2 below shows the variation in received solarchanges in the earth’s angle of tilt) and daily variation. UV-A radiation intensity throughout the day under clearThis variation is depens on the latitude and is mainly and cloudy weather conditions in Beirut (April andresponsible for the climate in that region. Regions near October 1985). With increasing cloudiness, lessthe aequator encounter lower variance of light intensity radiation energy is available. The reduction is dependingduring the year than those in the northern or southern on the wavelength as shown in Figure 3.Figure 1: Mean weekly values (solid line) and moving averages (broken line) for solar UVA-A radiation intensity (horizontal surface)18100%Intensity [W/m2]1614121086Cloudy Sky (April)Clear Sky (October)Available Energy [%]90%80%70%60%50%40%30%UV-AVisible Light420%210%09:00 10:00 11:00 12:00 13:00 14:00TimeFigure 2: Variation of UV-A intensity during daytime underdifferent weather conditions0%completelyovercastverycloudy50%overcastLevel of CloudinessslightlyovercastFigure 3: Losses of available solar energy at differentweather conditionscloudlessskyREFERENCESAcra, A., Jurdi, M., Mu'allem, H., Karahagopian, Y., Raffoul, Z.(1989). Water Disinfection by Solar Radiation - Assessmentand Application. Technical Study 66e. IDRC, 1989. ISBN 0-88936-555-5 [P5]Sommer, B., et al. (1997). SODIS-an emerging water treatmentprocess. J Water SRT-Aqua, 1997, 46, No. 3, 127-137.[P2]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 7Water Quality:Turbidity and Water DepthBACKGROUND INFORMATION SUMMARYRadiation intensity is reduced by increasing turbidity and water depth. Raw water of low turbidity (< 30NTU) should be used for SODIS. Similarly, the water depth should be small and not exceed 10 cm in orderto allow sufficient radiation of the water.Water TurbidityTurbidity is used as a parameter to characterise theoptical properties of liquids containing absorbers andscatterers; i.e. suspended particles. As shown inFigure1, high turbidity substantially reduces the lightpenetration in water and therefore reduces the disinfectionefficiency of the SODIS treatment process. Toensure safe water disinfection, the raw water shouldhave a low turbidity (less than 30 NTU=NephelometricTurbidity Units).Remaining UV-A Radiation [%]10090tap water,80turbidity < 1NTU70605040prefiltered water,turbidity 26NTU30 raw water,20 turbidity 40NTU1000 10 20 30 40Water Depth [cm]Water depthUV-radiation is reduced by increasing water depth. At awater depth of 10 cm and moderate turbidity level of26 NTU, UV-A radiation is reduced to 50%. The blacklower surface of SODIS bags and bottles induces atemperature gradient which causes the water tocirculate within the container thereby improving theinactivation efficiency. In any case, containers used forSODIS should be as flat as possible, with a water depthless than 10 cm.Water Turbidity TestTo decide whether the water needs filtering, place thefilled bottle on the SODIS Logo (see Figure below) ontop of a table in the shade (to avoid light interference)and look through the bottle from top to bottom. If youcan read the letters through the water, water turbidity isless than 30 NTU. If you can still see the sun rays of theLogo, turbidity is less than 20 NTU.If water turbidity is higher than 30 NTU, coarse andsettleable solids can be separated by storing the rawSDISSODIS Logo for Turbidity Test. If one can read the letters, theturbidity is less than 30 NTU. If one can see the sun rays ofthe Logo, turbidity is less than 20 NTU.water for one day, and turbidity can be reducedpossibly by flocculation / sedimentation (using alumsulphate or crushed Moringa oleifera seeds) or byfiltration.REFERENCESWegelin, M. et al. (1994). Solar water disinfection: scope of theprocess and analysis of radiation experiments. J WaterSRT-Aqua, 1994, 43, No. 3, 154-169. [P1]SODIS News No. 3, August 1998Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 10SODIS Efficiency:Influence of TurbidityBACKGROUND INFORMATION SUMMARYTurbid water protects the microorganisms from being irradiated. The microorganisms will therefore only beexposed to thermal effects. Hence, the raw water used for SODIS application should be as clear as possibleand not exceed a turbidity of 30 NTU.Turbidity effectsSuspended particles in water cause radiation scatteringby deflection from their surfaces in all directions.Turbidity is used as a parameter to characterise theoptical properties of liquids containing absorbers andscatterers.In short, turbidity• reduces solar radiation intensity(Figure 1)• protects microorganisms from being irradiated(being either under floating solids or in settleablesolids)• reduces the efficiency of the SODIS process(Figure 2)Influence of temperatureUV-A radiation intensity is more reduced in turbid thanin clear water, therefore reducing the SODIS-efficiency.However, the water temperature almost reaches thesame level as in non-turbid water. The microorganismsare therefore inactivated by the temperature rather thanby UV-A radiation. Table 1 shows some test results withbottles and bags at different levels of turbidity. With veryhigh turbidity, not all pathogens could be eliminated inthe bottle, because of the influence of the water depth(8 cm with bottle compared to 4 cm with bag).Nevertheless turbidity has only a moderate effect on theefficiency of SODIS, the raw water used should be asclear as possible and not exceed a turbidity of 30 NTU.Figure 1: Reduction of UV-A radiation as a function of waterdepth and turbidityRemaining UV-A Radiation [%]10090tap water,80turbidity < 1NTU70605040prefiltered water,turbidity 26NTU30 raw water,20 turbidity 40NTU1000 10 20 30 40Water Depth [cm]Figure 2: Inactivation of Faecal coliforms in 15 minutes underdifferent test conditionsAverage Reduction [%] in 15Minutes in Quartz Test Tubes454035302520151050Dark Control30 °CInactivation Faecal Coliforms in 15 MinutesTemp. only50 °CIrradiation only30 °CTest ConditionsTurb. >29 NTU50 °CTurb.

S DIS Technical Note # 11SODIS Efficiency:Covered Sky ConditionsBACKGROUND INFORMATION SUMMARYSuboptimal climatic conditions - as it is the case for covered sky - might require to expose the SODISbottles during two consecutive days. Sunlight exposure induces lethal effects to the microorganisms andhence, revival or regrowth has not been recorded.Suboptimal conditions in the fieldIn the field, optimal conditions can often not be found,i.e. covered sky instead of full sunshine (see alsoTechnical Notes 6). To encounter these problems, it isimportant to know that the die-off of microorganismsand pathogens is caused by several factors:• Light• Temperature• Nutrition• Humidity• TimePathogens cannot grow outside the human body, apartfrom some exceptions like salmonella.Prolonged SODIS operationWith covered sky, exposure for two consecutive days isneeded to reach the required radiation dose and toensure complete inactivation of the pathogens (seeFigure 1 as an example).Regrowth of microorganismsBacterial suspensions exposed to artificial UV-Cradiation are inactivated within a few seconds only.However, it is observed that bacterial regrowth occurswhich reaches the original cell density within a 1-weekperiod (Figure 2). In comparison, suspensions exposedto normal sunlight and for a longer period of time(several hours) did not result in a revival or regrowth ofE. coli even after prolonged storage periods of over twoweeks.However, the SODIS bottle exposed to sunlight is also abioreactor in which harmless bacteria mixtures canmultiply (Figure 2) as they would also do in the environment.Killing the pathogenic microorganisms is thetarget of SODIS and not the production of a sterilewater.Figure 2: Regrowth of E. coli and bacterial mixtures duringincreasing storage time of the irradiated supensions.Figure 1: Prolonged SODIS operation (3 days) of ● coliphagef2 and the animal viruses ❏ EMCV and ❍ rotavirus.log virus titer98765432nighttimenighttime100 10 20 30 40 50 60Time (hr)● E. coli irradiated using the undoped lamp and 320 nm cutofffilter❍ E. coli irradiated with sunlight❏ bacterial mixtures irradiated with sunlightREFERENCESWegelin, M. et al. (1994). Solar water disinfection: scope of theprocess and analysis of radiation experiments. J WaterSRT-Aqua, 1994, 43, No. 3, 154-169. [P1]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 12SODIS Efficiency:Laboratory versus Field ConditionsBACKGROUND INFORMATION SUMMARYThe SODIS water treatment method is simple and easy to apply. Nevertheless, people will have to beintroduced carefully to the process and trained. to handle it adequately.Laboratory tests and practical useThe conditions in practical SODIS application differ fromthe ones in laboratory and field test experiments. Theprocess is not applied under strictly controlled conditions,the material and methods used are often notoptimal and the handling of the treated water freqentlyinadequate.Furthermore, the inital Faecal coliform concentrationused in the experiments was often much higher(> 10’000/100 ml up to more than one million/100 ml)than commonly encountered in polluted rivers andponds (some 100 or 1000/100ml).Handling and trainingThe SODIS water-treatment method is simple to apply.Nevertheless, people will have to be introduced carefullyand get guidance about day-to-day application if theyare to benefit fully.There are different ways exposing the bottles of water tothe sun. The users are oftenis not aware that the placeused to expose the water to the sun should have fullexposure for about 4-5 hours.In the rural Melikan, 40% of the villagers have started toplace their containers on chairs or concrete floorswhich, compared to exposure on black rocks, corrugatedzinc or tile roofs, are not ideal conditions: Thedisinfection efficiency is lower, and only 50% of theexposed water samples were free of Faecal coliforms.After people received training and suitable, corrugatedzinc sheets, the number of inadequate applications wasreduced to 3%.The YDD (Yayasan Dian Desa) staff as SODIS projectteam treated in parallel to the users the same raw waterand achieved far better results. This experience illustratesthe importance of proper and continuous trainingof the users.Progress of SODIS handling in Indonesia. The bars show theremaining Faecal coliforms in the treated water. By training,the users became as successful in treating water as the YDDteam.Mistakes made☹ It is observed that some bottles are exposed tosunshine in the morning. But after two hours thearea is shaded by trees or the house.☹ It is also observed that many people like to puttheir bottles on a chair. At a certain point, the backpart of the chair shades the bottles.☹ Some users expose the bottle with the wrong sideto the sun, with the black part on top.No. of Faecal Coliforms [/100 ml]10000100010010Coliforms Before ProcessingColiforms After Processing, by LocalsColiforms After Processing by YDD1Jan Feb March April May June August SeptREFERENCESAristanti, Ch., Wegelin, M. (1998). Solar Water Disinfection.Water Treatment With Solar Energy. Internal Report. [R14]SODIS News, No. 1 February 1997. [R11]Wegelin, M., Sommer, B. (1998). Solar Water Disinfection(SODIS) - destined for worldwide use?. Waterlines, 1998,16, No. 3, 30-32. [P3]Yayasan Dian Desa (1997). Solar Disinfection System - FieldStudy. Final Report. [FInd3]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 13SODIS Use:Application ProcedureBACKGROUND INFORMATION SUMMARYSODIS works with the synergetic effect of water temperature and UV-radiation. The prescription given heremainly have the effect that sunlight and temperature are optimized. High water temperature is reached byusing black surfaces or black paint and not too large volumes of water per exposure area. Radiation doseis depending on the choice of the material for the container, location and orientation of the container,water depth, turbidity and exposure time.ContainersAdditional Prescriptions• Collect plastic bottles of 1-2 litre volume (preferablyPET bottles) generally available as soft drinkbottles• Use clean water free of settleable solids and of alow turbidity (max. turbidity > 30 NTU, see TechnicalNote #10, Influence of Turbidity, for more• Measure the light transmittance of the materialwith a photospectormeter (important is a goodtransmittance of the UV-A light, 320 - 400 nmspectrum)details). Separate coarse and settleable solids bystoring the raw water for one day and reduceturbidity possibly by flocculation / sedimentationusing alum sulphate or crushed Moringa oleifera• Check the water tightness of the bottles inclusiveseeds or by filtration.condition of the screw cap• Use aerated water. Standing water with a low• Clean the bottles thoroughly in- and outsidedissolved oxygen concentration should be aerated• Paint the bottles half-side black when black paintis availableby shaking the containers or swirling the waterwith a stick before filling the containers.• Observe a minimum exposure time to sunlight ofExposing Procedureone hour once the water temperature has reached• Fill the bottles completely with raw water50 °C. At high ambient temperatures and intensive• Screw the plug tightlysun radiation one might be able to use the containers• Expose the bottles in the morning hours to sunlighttwo times a day.on a place which is irradiated the full day• Expose the water for five hours during a sunny day• Place the bottles in horizontal position on a firmblackened support, preferably on a corrugated ironsheet/roof or on a tile roofin case the water temperature has not reached therequired 50 °C. Should the sky be covered withclouds expose the water for two consecutive days• Collect the bottles in the late afternoon and bringbefore consuming it.them to a safe place for cooling• Collect rain water from a clean area (e.g. from a• Consume the treated water directly from the bottleusing a clean glass or a cup, store it possiblyovernight for additional coolingcorrugated or tile roof) during rainy days to coveryour drinking water demand.REFERENCESWegelin, M., Sommer, B. (1998). Solar Water Disinfection(SODIS) - destined for worldwide use? Waterlines, 1998,16, No. 3, 30-32. [P3]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 14SODIS Use:Guidelines to Increase EfficiencyBACKGROUND INFORMATION SUMMARYTreatment efficiency can be increased by a sound application of SODIS. One important method is toenhance water heating through the use of half-blackened bottles and black zinc sheets as support of thebottlesIn the field, the process is not applied under strictlycontrolled conditions, the material and methods usedare often not optimal, the raw water pollution is generallymuch lower and the handling of the treated waterfrequently inadequate.Optimizing water heatingThe treatment efficiency can be increased by applyingsimple methods as listed below. Our method is to usehalf-blackened plastic bottles which achieve approx.5°C higher water temperature as compared tounpainted bottles (see Figure 1). Another method is toplace the plastic bottles on a black zinc sheet instead oflaying them on a floor. This arrangement will alsoincrease the temperature by approx. 5°C (see Figure 2).Both methods have the effect that the microorganismsare longer exposed to a period of increased temperatureby a faster heating up of the water. This willenhance the inactivation effects.Factors that reduce the efficiency• Turbid water• Bottles with low UV-A transmittance• Low air temperature• Cloudy sky• Bottle placed upright instead of horizontalMethods to enhance the efficency• Use raw water with low turbidity• Use half-side black painted plastic bottles• Place container to a place which is exposed to thesun the full day• Place the container on a corrugated zinc sheet• Expose containers for two consecutive days oncloudy days• Replace old and scratched bottlesWater Temperature (°C)10:0010:1510:3010:4511:0011:1511:3011:4512:0012:1512:3012:4513:0013:1513:3013:4514:0014:1514:3014:4515:00Figure 1. Comparison of water temperature in half-blackenedSODIS bottles and clear bottles (cement floor, no black zincsheet, no wind protection).Water Temperature (°C)555045403530255550454035302511.00painted bottleunpainted bottleTimerangepaintedbottlerangeunpaintedbottle11.1511.3011.4512.0012.1512.3012.4513.0013.1513.3013.4514.0014.1514.3014.4515.00Weather Condition(% cloudiness)TimePainted BottleUnpainted Bottle100%90%80%70%60%50%40%30%20%10%0%Weather Condition(% cloudiness)Figure 2. Water temperature in painted and unpainted SODISbottles placed on a black zinc sheet. The bars illustrate thecloudiness.REFERENCESSODIS News No. 3, August 1998. [R13]Yayasan Dian Desa (1997). Solar Disinfection System - FieldStudy. Final Report. [FInd3]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 15SODIS Use:AcceptanceBACKGROUND INFORMATION SUMMARYHigh acceptance of SODIS is recorded as the useres appreciate the sustainable and simple water treatmentmethod. Nevertheless, careful introduction of the process best through community participation isrequired to achieve good respond.Introducing new equipment and facilitiesPeople’s health will not improve just because they havenew equipment or facilities - they have to use them.Minor improvements to existing water supply practicesare more likely to be accepted than major and suddenchanges. SODIS will only be used and applied if thetarget population is convinced of its advantages overthe traditional ways of treating and handling drinkingwater. Consumers need to be fully aware of the bacteriologicaltransmission routes of water-borne diseasesand how to reduce or avoid them. Finally, private userswill only invest in water treatment if they believe they willbenefit directly - as health benefits are often indirect,they may be perceived only in the long-term.Field ExperienceThe objective of the SODIS demonstration projects,conducted by local institutions in seven differentcountries, was to study the socio-cultural acceptanceand affordability of this treatment option. The recentlycarried out survey revealed that an average of 84 % ofthe users will certainly continue to use SODIS afterconclusion of the project, and about 13 % consider(maybe) using it in the future. Only 3 % refuse to useSODIS as their health is allegedly not affected by thepresent water quality. The figures obtained from twocountries differ from the overall survey results inasmuchas the percentage of “maybes” was comparatively highin Burkina Faso (30 %) and China (45%). Involvement ofthe users in the projects was hardly observed in thesetwo countries. In China, around half of the peopleinterviewed said they still drink untreated water eventhough they are aware that the quality is poor.Reasons stated by those who accept andcontinue practising SODIS• Easy and practical• It provides good and clean drinking water• Less working time and burden for daily activities(no boiling means no starting fire, no fuel, nowashing up the kettle)• No pathogens anymore, less sickness, lessdiarrhea, no stomachaches• It saves costs (firewood, fuel)• It saves time• Status• Improves villagers quality of lifeTable 1: Results of the SODIS acceptance evaluationReasons given by those who don’t continueusing SODIS• Not trust in the results that bacteria can be killedjust by exposure to sunshine• Too long, not patience• Water taste and smell plastic (especially thoseusing plastic bags)• Lack of materialsI will continue to use SODISCountry certainly maybe probably definitelynot notColombia 90 8 0 2Bolivia 93 0 0 7Burkina Faso 70 30 0 0Togo 93 0 0 7Indonesia 90 5 3 2Thailand 97 0 0 3China 55 45 0 0average 84 12.6 0.4 3REFERENCESAristanti, Ch., Wegelin, M. (1998). Solar Water Disinfection.Water Treatment With Solar Energy.. Internal Report. [R14]Environmental Concern (EC) Khon Kaen (1997). SODISDemonstration Projects. Khon Kaen, Thailand. Finalevaluation. [FTha3]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 16SODIS Use:CostsBACKGROUND INFORMATION SUMMARYSODIS is a low-cost technology. The required annual capital costs amount to a approx. 2-5 $ per household,the operation consts are practically zero. Saving due to reduced energy and medical care expendituresare expected benefits.Willingness to paySavingsThe factors influencing willingness to pay are rather Health benefits are difficult to quantify. Higher productivitythrough improved health and reduced costs requiredcomplex and manifold. However, willingness to pay for aservice or commodity is essentially demand-driven. The for medical treatment are the expected benefits.ability to pay is dependent on the level of income and Reduced energy costs are a second benefit.costs of the provided service or commodity. Acces togood quality water, especially in terms of bacteriological In Melikan (Indoniesia) for example, about 50% of thequality, is often not a felt need, particuarly not under firewood consumption is used for water treatment“normal” pulic health conditions when several diarrhoeal (boiling). In average, each household spends more thanincidences per year are regarded as normal. Hence, Rp. 600 every day for the necessary firewood, whereaswillingness to pay for water quality improvement may the price for a SODIS bottle (that can be used for a longgenerally be low.time) amounts to only Rp. 500. Although water ispurchased from a well owned by the government orEconomic considerationsfrom a private company, the water still has to be boiledThe costs are divided into investment (cost of bottles) for domestic purpose.and operating & maintenance costs. The latter ones areneglectable, since solar energy is free of charge. Thecosts for PET bottles vary from country to country andusually amount less to than 0.5 US$/bottle:China 0.14 US$Thailand 0.3 US$Colombia 0.4-0.6 US$Indonesia 0.07 US$ (Rp. 500)The annual costs for a household of 5 persons wouldamount 3 US$ only. (2 bottles per person at a price of0.3 $ per bottle). The full costs for the bottles should bebeared by the user of SODIS in order to achieve a realeconomic sustainability.Project CostsSODIS has to be introduced and disseminated by localinstitutions (NGO, government). These costs cannot bepaid by the private users, but by public funds (grant ofdonors, governmental services).REFERENCESYayasan Dian Desa (1997). Solar Disinfection System - FieldStudy. Final Report. [FInd3]SODIS News No. 2, August 1997. [R12]Ueberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch

S DIS Technical Note # 17SODIS Use:SODIS Bags and Temperature SensorsBACKGROUND INFORMATION SUMMARYSANDEC developed different prototype material which has been field tested in the SODIS demonstrationprojects. SODIS plastic bags were used to attract the interest of the people on the new water treatmentmethod. Temperature sensors have been distributed to record whether the threshold water temperature of50 °C has been attained or not.Use of SODIS BagsUse of Temperature Sensor• Fill half of the bags with raw waterThe SODIS Temperature Sensor (TS) is an aid for the• Drive the air out of the bags and close themuser. It does not influence the SODIS process but is an• Place the bags in the morning hours on a spotreceiving full sunlight throughout the dayindicator for the expected efficiency. When the temperatureof 50°C is reached, the paraffine inside the TS• Place the bags in horizontal position on a firmblackened suport, preferably on a corrugated ironsheet/roof or tile roofmelts and drops to the bottom. At this temperature,SODIS needs just one hour to inactivate the pathogens.The following day, the TS can be reused by pulling the• Collect the bags in the late afternoon and storethem in a safe place for coolingscrew to the opposite side of the paraffine and placingthe TS inside the bag or bottle again (see Figure below).• Consume the treated water directly from the bagusing a clean glass or cup, store it possiblyovernight for additional coolingWhen 50°C are not reached, the paraffine doesn’t melt.If that’s the case, the SODIS bag or bottle must beexposed for at least five hours to ensure inactivation. Onvery cloudy days and/or low temperature, an exposurefor two consecutive days should be considered (seealso Technical Note #11, Covered Sky Conditions).5 l2 - 3 l123Use of the Temperature Sensor. After the paraffine hasmelted down, the screw is pulled up, making the sensorready for use again.45REFERENCESUeberlandstr. 133, CH-8600 Duebendorf / Switzerland http://www.sodis.chPhone +41-1-823 50 19 Fax: +41-1-823 53 99 http://www.sandec.ch