Frequently Asked Questions about Sodium Hypochlorite (SH)

Sodium hypochlorite is highly reactive and volatile. At normal pH (6-8), sodium hypochlorite can degrade substantially within 2-3 weeks. This shelf life is not ... Skipdirectlytositecontent Skipdirectlytopageoptions SkipdirectlytoA-Zlink GlobalWater,Sanitation,&Hygiene(WASH) SectionNavigation CDCHome Facebook Twitter LinkedIn Syndicate FrequentlyAskedQuestions(FAQs)aboutSodiumHypochloriteSolution(SH) Minus RelatedPages FAQaboutSodiumHypochloriteSolution(SH) 1.Issodiumhypochlorite(SH)thebestdisinfectanttouse? Investigationshaveshownsodiumhypochloritetobeaneffectivedisinfectanthavingbroadapplications.Althoughanumberofotherdisinfectants(calciumhypochlorite,ozone,UV,solardisinfection)andtreatmentprocesses(filters,slowsandfiltration)havebeeninvestigated,sodiumhypochloriteappearstoofferthebestmixoflowcost,easeofuse,safety,andeffectivenessinareaswherethereisenoughwatertodrinkandwaterisnotexcessivelyturbid.ThesecharacteristicsarethereasonswhymostwatertreatmentsystemsintheUSandEuropehavebeenusingchlorinefordisinfectingdrinkingwaterfornearly100years.Theotherdisinfectionmethodsnotedabovealsoeffectivelydisinfectwaterandareusefulinanumberofsettings. 2.Whataboutusingcalciumhypochlorite(HTH)orchlorinetabletsinstead? Chlorinetabletsand/orHTH(alsonamedcalciumhypochlorite)arewidelyavailableinsomeareas.AnumberofpotentialusersoftheSWSknowthatthesetabletsareusedtodisinfectwater.Unfortunately,wehavealsofoundthatmanypeoplehavedifferentlevelsofknowledgeregardingappropriatedosinginstructions,whichisaconcernbecausethetabletsvarysignificantlyinstrength.InHaiti,asmallsaranwrapbagofapproximately100HTHpelletsiswidelyavailableandinexpensive.However,thepelletsvaryinsize,thequalityofthepelletsisunknown,and,dependingonimpuritiesinthemanufacturingprocess,theycandegradequickly.Inothercountries,veryhighstrengthtabletsmaybesoldwhich,whenaddedtowaterfordisinfection,leaveastrong,unpleasanttaste.ItisimportantforuserstoknowthequalityandstrengthofHTHand/orchlorinetabletsandunderstandtheappropriatedosingstrategybeforeattemptingtousethemfordrinkingwatertreatment;inmostinstances,however,thisisimpossibleforuserstodo.Forthesereasons,hypochloritesolutionislikelytobeabetteroption. 3.WhatcharacteristicsarerequiredforSH? First,itisimportantthattheconcentrationoftheSHsolutionproducediscorrect(usually0.5to1.0%).Aconcentrationthatistoolowrequirestoohighavolumetoadequatelytreatenoughwatertobepractical.Aconcentrationthatistoohighisdifficulttoaccuratelydose,raisingtheriskoftoohighadose(whichisunpalatable),ortoolowadose(whichmightnoteffectivelydisinfectthewater).Second,itisimportantthatthepHlevelofthesolutionbeatleast11.Thisincreasestheshelflifeofthesolution. 4.HowdowedeterminetheappropriateSHdose? Thehypochloritedosewilldependonthecharacteristicsofthelocalwater.Usuallyanamountintherangeof5to10millilitersaddedto20litersofwaterissufficienttoinactivatethedisease-causingorganisms,butnotleaveanunpleasanttaste.Oncethesizeofthecapforyourprojecthasbeendetermined,somesimpleexperimentscanbeusedtodeterminetheappropriatedose.Toconducttheexperiments,youwillneedlocallyavailableSH,sourcewaterinyourarea,andakitthatmeasurestheamountoffreeandcombinedchlorine.Pleasecontacthealthywater@cdc.gov formoreinformationonhowtocompletethistesting. 5.HowdoyouensureadequateshelflifeofSH? Sodiumhypochloriteishighlyreactiveandvolatile.AtnormalpH(6-8),sodiumhypochloritecandegradesubstantiallywithin2-3weeks.ThisshelflifeisnotadequateforuseintheSWS,whichrequiresthatthehypochloriteremainatahighenoughconcentrationtoinactivatedisease-causingorganisms.ByraisingthepHofthehypochloritesolution,youstabilizethesolution.ThepHcanberaisedbytheadditionofsodiumhydroxide,whichiswidelyavailable.Inordertodeterminetheamountofsodiumhydroxidetoaddtoyoursodiumhypochloritesolution,youwillneedtocompletetrial-and-errortesting.Addaknownvolumeofsodiumhydroxidetoaknownvolumeofsodiumhypochlorite,andthenmeasurethepHwithameterorkit.Becausesourcewaterqualityisdifferentineachlocation,thereisnotonestandardvolumeofsodiumhydroxidetoaddtoensurepHisabove11.Youwillhavetostartwithaknownvolume(perhaps1tablespoonin1gallon,or5mlin1liter)andcompleterepeattrial-and-errortesting.TheexactpHisnotimportantinthiscontext—yousimplyneedtoensurethatthepHlevelisabove11. 6.WilladdingNaOHchangetheeffectivenessofSH? No,becausewhenthesodiumhypochloritesolutionisaddedtowater,thewaterdecreasesthepHandthesodiumhypochloritebecomesmoreactive.Thechemistrybehindthisis:thepHscaleisfrom0to14.AcidshaveapHbelow7,basesareabove7,and7isneutral.MostnaturalwaterisaroundpH6-7.Whensodiumhypochloriteisinwater,itisamixtureoftwocompounds,withtheconcentrationofeachcompounddependentonpH.Oneofthesecompoundsissignificantlymorereactive,volatile,andmoreeffectiveatinactivatingbacteriathantheother.AthighpH(above11)themajorityofthesodiumhypochloriteisintheformoftheless-reactivecompound.Thus,whenyouaddsodiumhydroxidetothesodiumhypochlorite,youareconvertingitintotheless-reactiveform.However,waterisaroundpH6-7.Whenyouaddasmallamount(5milliliters)ofsolutionatpH11toalargeamount(20liters)ofwateratpH6-7,themixturebecomespH6-7.Thus,whenyouaddthehypochloriteatpH11toyourwaterintheSWS,youconvertthehypochloritebackintothereactiveform,andthenitinactivatesthedisease-causingorganisms. 7.IfyouaddSHtowateralreadytreatedinamunicipalwatertreatmentplant,isthereariskofachlorineoverdose? Thisisveryunlikely.Ifsodiumhypochloriteisaddedtowaterthatisalreadytreated,thewaterwouldmostlikelystillbewithinanacceptablerangeofchlorineresidual.Typically,chlorinatedurbanwatersystemshavefreechlorinelevelsofaround0.1to0.5partspermillion.Wecalculateoursodiumhypochloritesolutiondosetogiveuntreatedwaterafreechlorinelevelofaround1partpermillion.Soifyouaddoursolution(toachieve1partpermillion)totreatedurbanwater(0.1-0.5partspermillion),thelevelofthe“overtreated”waterwouldstillbeintheacceptablerangeof0.5-2partspermillion(whichistherangethatbalancesdisinfectionefficacyandreasonabletaste). 8.Whydoesfreechlorineintreatedwaterdeclineovertime? Chlorineisanextremelyreactivechemical.Rightafterthesodiumhypochloriteisaddedtothewater,chlorinelevelsdeclinebecausethechlorineisreactingwithinorganicandorganicmatterandmicrobes.Afterthosereactionsarecomplete,chlorineinwaterwillslowlyescapeintotheairasagas.Thisisthereasonthatfreeandtotalchlorinelevelsslowlydegradeovertimeinacovered(butnotsealed)container,andalsowhyitisrecommendedthatthepHlevelofthehypochloritesolutionberaisedtoover11toextendtheshelflifeofthesolutionbeforeitisused. 9.WhathappensifachildaccidentallydrinksSH? ItisimportanttorememberthattheconcentrationoftheSHusedintheSafeWaterSystem(SWS)isapproximately0.5-1.0%.Areviewofhealtheffectsfromaccidentalandintentionalingestionoffullstrengthbleach(sodiumhypochlorite),whichis5-6%,inEuropeanpoisoncontrolcenters1showedthat“acuteaccidentalexposuretohouseholdbleachinuseorinforeseeablemisusesituationsresults,inthegreatmajorityofthecases,inminor,transientadverseeffectsonhealth. Theauthorsalsocitedtwostudiesspecificallyonchildren:1)AstudyinChicagoshowingthatof26childrenadmittedforaccidentalbleachingestion,onlyonehadamoderatehealtheffect(irritationoftheesophagus,whichhealedonitsownwithoutintervention),withtheremainingchildrenhavingonly“minortransientirritationeffects”,and2)Astudyof23casesaged1–3years,withonlyonecasehaving“superficialburnsintheesophagus”,whichdisappearedtwoweekslater.Suicideattemptsinadultshaveshownthatalethaldoseofsodiumhypochloritevarieswidely,withlethalresultsat200-500mLof3-12%strength.Asmentionedabove,thehypochloriteingestedinthemajorityofthecasesinthereviewwasfullstrengthhouseholdbleach:5-6%.SeveralfactorsmakeitunlikelythatthehypochloritesolutionsrecommendedintheSafeWaterSystemcouldcauseharmrememberingthatinmostcountries,theSWSSHissoldin250mlbottles;insomecountries,the500mlbottlesareused.First,itisunlikelythatachildwouldaccidentallydrink250or500millilitersofsomethingthattastesasbadasthesodiumhypochloritedoes.Second,itisevenlesslikelythat,atthelowconcentrationusedinthisproject,anythingharmfulwouldoccur.Despitethesesafetydata,itis highlyrecommendedthatpartoftheeducationalmaterialsemphasizetheneedtokeepthesodiumhypochloritesolutionstoredsomewheresafe(outofsunlight,sealed,awayfromchildren)forhealthreasons;toprotectthesodiumhypochloritefromdegradation;andtopreventspillsinhouseholdsthat,duetolimitedincomes,wouldbeunabletopurchasemoresolution. 10.DoesSHinactivateGiardiaandCryptosporidium? GiardiaandCryptosporidiumarebothprotozoaandarehighlytoleranttochlorinationbecausetheyexistinwaterinacystoroocystform.ThehardcoatofthecystsoroocystsprotectsGiardiaandCryptosporidiumfrombeinginactivatedbychlorine.CryptosporidiumismuchmoreresistanttochlorinethanGiardia(seepathogeninactivationtableformoredetails).Bothprotozoa,however,arefairlylarge,whichmeansthattheycanberemovedbyfiltration.IfGiardiaorCryptosporidiumareasignificanthealthproblemintheprojectarea,afiltrationstep(throughceramic,sand,orotherfilters)canbeaddedbeforeaddingthesodiumhypochlorite. 11.Whatdowedoifthesourcewateristurbid? Waterthatlooksdirtyorcloudyiscalledturbidwater.Turbidityisameasureoftheamountoflightthatisscatteredasitpassesthroughthewatersample.Ifmoreparticlesareinthewater,morelightwillbescattered,andtheturbidityisthushigher.Waterthatlooks“dirty”willhaveahigherturbiditythanwaterthatlooksclear.Turbidityisoftenusedtorepresenttheamountoftotalsuspendedsolidsandtheamountoforganicmatterinthewater.Bacteriaandotherpathogensmayalsosticktoparticlesinthewatersohighturbiditymayincreasethechancethattherearepathogensinthewater.Therearetwoissuesassociatedwithaddingchlorinetowaterthathasahighturbidity:1)Chlorinereactsequallywithalltheorganicmaterialinthewateraswellaswiththebacteriaandotherpathogens.Ifthereisagreatdealoforganicmaterialthenitwilltakemorechlorinetofullyreactwithallthedissolvedsolidsandorganicmaterialaswellasinactivatethebacteriaandotherpathogens,2)Thereisapotentialforcreatingmoredisinfectionby-productsifthereisahigherconcentrationoforganicmatterinthesourcewater.Therearethreestrategiesthatcanbeusedtotreatturbidwater:1)Filterthewaterthroughaclothfiltertoremovesomeoftheorganicmatterandthenchlorinate;2)Letthewatersettlefor12-24hourssotheorganicmatterandsolidsfalltothebottomandthenpourofftheclearerwaterintoaseparatevesselwhereitisthenchlorinated;or3)Increasethedoseofsodiumhypochloritesolutionaddedtotheturbidwatertobesurethereisenoughchlorinetoinactivatethedisease-causingorganisms.Becauseeverycommunityisdifferent,experimentstodeterminewhichisthemostacceptable,appropriate,andeffectivestrategywillneedtobeconductedintheprojectcommunity. 12.Whataredisinfectionby-products,andaretheyanissueintheSWS? Disinfectionby-products(DBPs)arechemicalcompoundsformedwhenchlorineisaddedtowaterwithorganicmaterialinit.Allnaturalwatershavesomeorganicmaterialinthem,andgenerallywatersthataremoreturbid(dirty)havemoreorganicmaterial.DBPsareaconcernwheneverchlorineisaddedtodrinkingwater,whetherintheSafeWaterSystemorinalarge-scalewatertreatmentplantintheUnitedStates,becausesomestudiessuggestthatingestionofDBPsinwateroveralifetimemaybeassociatedwithaverylowriskofcancer.However,thisriskisverysmall.Inareaswheremanypeople,andmanychildren,havediarrhealdiseasescausedbyunsafedrinkingwater,theriskofcancerfromDBPsisverysmallcomparedtotheriskofdeathorstuntingfromdiarrhealdiseases.IntheirGuidelinesforDrinking-waterQuality,theWorldHealthOrganizationstates:“Wherelocalcircumstancesrequirethatachoicemustbemadebetweenmeetingeithermicrobiologicalguidelinesorguidelinesfordisinfectantsordisinfectantby-products,themicrobiologicalqualitymustalwaystakeprecedence,andwherenecessary,achemicalguidelinevaluecanbeadoptedcorrespondingtoahigherlevelofrisk.Efficientdisinfectionmustneverbecompromised”2.Formoreinformation,pleaseseeourdetailedpageonDBPs. 13.WhyshouldIinvestinahypochloritegenerator? Anumberofcompaniesmanufacturehypochloritegenerators.Thereareseveraladvantagesinusingahypochloritegenerator.First,localproductionofthesodiumhypochloriteminimizestransportationcosts.Second,intheeventthereisnotareliablebleachproducerinthecountry,thehypochloritegeneratorcanprovidethecapacity.Third,revenuesfromthesaleofthesolutioncanbeusedtohelpsupportoperationandmaintenanceofthemachineandtopaytheoperator.Considerationsthatmustbetakenintoaccountwhenproducingbleachinthiswayincludetheneedforregularoperationandmaintenanceofthemachine,theneedtotesttheconcentrationandpHoftheSHsolutionproduced,paymentofareliablepersontooperateandmaintainthemachine,replacementofthecellofthegeneratorevery5years,andtheneedforareliableelectricitysupply. 14.ArethereadvantagestohavingaprivatecompanymanufactureSH? Thereareseveraladvantagestohavingacompanymakethesolution:1)Mostlikely,allacompanywouldneedtodotomakethedesiredconcentrationofhypochloriteistodiluteanexistingbleachproduct.2)Ifdemandforthesolutiongrows,acompanyisbetterabletoexpandproduction.3)ManycompanieshavecertificationfromBureausofStandardsforbleachproductsthatcanoftenbeappliedtothenewdilutesolution.4)Mostreputablecompanieshavequalitycontrolprocedures.Incountriesaroundtheworld,PopulationsServicesInternationalexternalicon(PSI–asocialmarketing,non-governmentalorganizationthathassuccessfullyimplementedanumberofSWSprojects)hasoptedtohaveprivatecompaniesmakethebleachforthem. 15.HowmuchdoesitcosttomanufactureSH(peryear)? Inthefirstyearofthecountry-scaleprojectinZambia,itcostUS$78,000tomanufacture400,000bottles.Thelaborcostwas$23,000andthematerials(salt,vinegar,bottles,andlabels)costwas$55,000.ThetotalproductioncostwasthereforeUS$0.20perbottle.Assumingafamilyusageofonebottlepermonth,theproductioncostforayear’ssupplyforonefamilyisaboutUS$2.40.Afterthefirstyear,costsusuallydecrease.Costsvarybycountry,dependingonlabor,materials,andvalue-addedtaxes.Insmall-scaleprojectsusingalocalhypochloritegeneratorandreusablebottles,theproductioncostofthehypochloriteisonlythecostofthesalt,water,labor,andelectricity. 16.WhatcharacteristicsdoyourecommendfortheSHbottle? CDCrecommendsthefollowingsixcharacteristicsforthesodiumhypochloritebottlethatiskeptinthehome:1)Thesizeofthebottleshouldbebetween250and500milliliters.Thisissmallenoughtobeaffordableandtoensurethatthesolutionwillbeusedbeforeitdegrades,butlargeenoughthatitwilllastafamilyforapproximatelyonemonth.2)Theneckofthebottleshouldbecompatiblewithsodabottlecaps,whichtendtobemass-produced,inexpensive,typicallyhavethedesiredvolumeof5-10mLfordosing,andareavailableinmostlocations.3)Thevolumeofthecapshouldbebetween5and10mlsothatitcanbeusedtodosethesolution.4)ThebottleshouldbecomposedofanopaqueplastictopreventexposureofthesolutiontodirectUVradiationfromsunlight,whichwilldecreaseitsshelflife.5)Theneckandcapshouldhaveatleastfourthreadstoimprovetheseal.Thecapshouldhavearaisedringinsidetohelpsealthebottle,aswell.6)Ahandleisnotnecessary.Thisonlyincreasesthecostanddecreasesthespaceavailableforinstructions. 17.HowcanwesavemoneyonmanufacturingtheSHbottle? Onewaytosavemoneywhendesigningthesolutionbottleistodesignthebottlesothatanalreadylocallyavailablecapwillfitit.Werecommendaplasticsoftdrinkbottlecapwithavolumeof5–10milliliters.Usingalocallyavailablecapwillsaveyoufromhavingtopurchaseamoldforthecaps,andsoftdrinkcapsaretypicallymassproducedatverylowcost.Theexistingcapsmustfittightlyandsecurelyontheprojectbottledesign. 18.HowcanyoudistributeSHthroughoutthecountry? Inmanyprojects,PSIhasinitiatedsocialmarketingcampaigns,whichincludeactivatingnetworksofwholesaleandretailoutletsandfacilitatingdistributiontocommunitieswherevulnerablepopulationslive.Forsmallerprojects,oneideaistopurchasespaceonprivatedeliverytrucksthatarealreadygoingtotargetlocationstodelivergoodssuchassoftdrinksandbeer,ortorequestadonationofspacebytheprivatecompaniesasacharitableactivity. Pagelastreviewed:January10,2022 Contentsource: CentersforDiseaseControlandPrevention,NationalCenterforEmergingandZoonoticInfectiousDiseases(NCEZID),DivisionofFoodborne,Waterborne,andEnvironmentalDiseasesatCDC homeGlobalWater,Sanitation,&Hygiene(WASH) CommunityWaterSystems HouseholdWaterTreatmentplusicon Chlorinationplusicon EffectonPathogens FreeChlorineTesting Pre-TreatmentMethods DisinfectionBy-Products FrequentlyAskedQuestionsaboutSodiumHypochlorite(SH) Flocculant/DisinfectantPowder SolarDisinfection CeramicFiltration SlowSandFiltration Sanitation&Hygieneplusicon HygieneinResource-LimitedSettings Toilets&Latrines PotentialSanitationSolutionsDuringanEmergencyResponse GuidanceforWorkersHandlingHumanWasteorSewage ManagementofFecalWaste WASHinHealthcareFacilitiesplusicon DataCollectionToolsandCommunication InnovationsfortheField WhereWeWork Travelers’Health PublicHealth&MedicalProfessionals Publications,Data,&Statistics HealthPromotionMaterialsplusicon Posters Booklets FactSheets Podcasts Videos WorldToiletDay Training&Education CDCatWork:GlobalWASHplusicon StoriesfromtheFieldplusicon CDChandhygieneeffortsinWesternKenya WASHTrainingforOutbreakResponseinSierraLeone CDCFightsCholerainCameroon UsingSolarEnergytoTreatWasteinKenya InternationalOutbreakInvestigations TheSafeWaterSystemplusicon StoriesfromtheField TheCDCSWSContainer Policy&Recommendationsplusicon DiseaseThreatsandGlobalWASHKillers GlobalWASHHealthBurden AssessingAccesstoWater&Sanitation FastFacts HealthyWaterSites HealthyWater DrinkingWater HealthySwimming GlobalWASH OtherUsesofWater WASH-relatedEmergencies&Outbreaks Water,Sanitation,&Environmentally-relatedHygiene Facebook Twitter LinkedIn SAS stats ExitNotification/DisclaimerPolicy Close LinkswiththisiconindicatethatyouareleavingtheCDCwebsite. 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