drinking water chlorination - world chlorine council · 2 drinking water chlorination • world...

Drinking Water Chlorination

2 DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008

The use of chlorine to protect drinking water

is one of the greatest public health advances in history. Chlorine

destroys disease-causing organisms in water and is the most

commonly-used disinfectant in all regions of the world.

The World Chlorine Council® (WCC) has published this paper to briefly

address key issues related to drinking water chlorination:

• Chlorine’scriticalroleinprovidingsafedrinkingwateraround

the globe;

• Potentialhealthandenvironmentaleffectsofchlorineand

disinfection byproducts in treated drinking water; and

• Considerationsforselectingdisinfectionmethods.

TheWorldChlorineCouncil(WCC)isaglobalnetworkrepresentingthechlorineandchlorinatedproducts

industries.Formedin1993,theWCCcurrentlyrepresentsover23national/regionalassociationsinover

27countriesaccountingforover80percentofglobalchlorineproduction.TheWCCworksto improve

awarenessof thebenefitsofchlorinechemistry; further thepracticeandunderstandingof responsible

stewardship;andanticipateandrespondtorelevanthealth,environmentalandpublicpolicyissues.

DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008 3

Helping to provide safe drinking water around the globe

Chlorine is effective, affordable, and widely available for disinfection

Chlorineisusedtodestroydisease-causingorganismsinwater,anessentialstepindeliveringsafe

drinkingwaterandprotectingpublichealth.Chlorineisbyfarthemostcommonlyuseddisinfectant

inallregionsoftheworld.Wherewidelyadopted,chlorinehashelpedtovirtuallyeliminatewater-

bornediseasessuchascholera,typhoidanddysentery.Chlorinealsoeliminatesslimebacteria,molds

andalgaethatcommonlygrowinwatersupplyreservoirs,onthewallsofwatermainsandinstorage

tanks.Only chlorine-baseddisinfectants leaveabeneficial“residual” level that remains in treated

water,helpingtoprotectitduringdistributionandstorage.

Chlorine isaversatileand low-costdisinfectantappropriate foranysizewater system,whether it

servesaremoteruralvillageoralargemoderncity.Wherepipedwatersuppliesarenotavailable,

chlorinecanalsobeused for treatingwater in individualhouseholds.Specially-packagedchlorine

bleachcandisinfecthouseholdwaterforlessthanUS$4/yearperfamily.

In addition, chlorine is critically needed for emergency relief efforts. In responding to the 2004

tsunamidisasterinSouthAsia,theWorldHealthOrganization(WHO)reported,

“Chlorine is most widely and easily used, and the most affordable of the drinking water

disinfectants. It is also highly effective against nearly all waterborne pathogens.”

Water and sanitation: A global health crisis

Morethanonebillionpeopledonothaveaccesstoasafewatersupplywithin1kmoftheirhomes,

relyinginsteadonunprotectedlakes,streamsorshallowwellstomeethouseholdneeds.Evenwhere

relativelycleanwaterisavailableatacommunitysource,itcaneasilybecontaminatedasit iscol-

lected,carriedandstoredinthehome.WHOestimatesthatmorethan4,000peopledieeachday

fromdiarrhoealdiseasesresultingfromunsafewaterandlackofsanitation.Ninetypercentarechil-

drenundertheageoffivewholiveindevelopingcountries.

Safe water: Essential for sustainable development

TheUnitedNationshasrecognizedthecriticallinkbetweensafewaterandsustainabledevelopment.

Accesstosafewaternotonlyreducesdisease,butalsoprovidesarangeofeconomicbenefitsfora

community.

Atthe2002WorldSummitonSustainableDevelopment,theUnitedNationsreaffirmeditscommit-

menttoreducebyone-halftheproportionofpeoplewithoutaccesstosafewaterby2015.Meeting

thisgoalwillrequiresustained,coordinatedactionandenormousinvestmentseachyear.WHOhas

concludedthatglobalinvestmentstoimproveaccesstosafewateraccesswillyielddirectandindirect

benefitsthatfarexceedtheassociatedcosts.


Chlorine and disinfection byproducts in drinking water do not pose significant health or environmental risks

Chlorine in drinking water is safe for consumption

Thesmallamountofchlorinetypicallyusedtodisinfectwaterdoesnotposeriskstohumanhealth.The

WorldHealthOrganization(WHO)hasestablishedaguidelinevalueof5mg/Lforchlorineindrinking

water,meaningthatsuchconcentrationsareconsideredacceptableforlifelonghumanconsumption.

Furthermore,WHOconcludesthatthisvalueis“conservative,”asnoadverseeffectsfromchlorinein

drinkingwaterwereobservedinstudiesreviewedbyWHO.

DBPs should be controlled, but disinfection must never be compromised

Anothersafetyconsiderationfortreateddrinkingwaterisdisinfectionbyproducts(DBPs),chemical

compoundsformedunintentionallywhenchlorineandotherdisinfectantsreactwithcertainorgan-

icmatter inwater.Alldisinfectants formDBPs,althoughmuchmore isknownaboutchlorination

byproducts than isknownaboutthebyproductsofotherdisinfectants.Forexample, toxicological

studiessuggestthatsometrihalomethanes(THMs)arecarcinogenictolaboratoryanimals,butonly

atlevelsmanythousandsoftimesgreaterthanthosefoundindrinkingwater.Researchhasshown

thatchloroform(themaintypeofTHM)isunlikelytocausecanceratextremelylowlevelsfoundin

drinkingwater.WhilethepotentialhealthrisksfromDBPsaresmallanduncertain,highlevelsofthese

chemicalsarecertainlyundesirable.WHOhasestablishedguidelinevaluesforseveralDBPs,including

trihalomethanes.

Guideline values for chlorine and trihalomethanes

WHO Guidelines for drinking water quality (2004)

Chlorine below5milligramsperliter(mg/L)*

Bromodichloromethane below0.06mg/L

Bromoform below0.10mg/L

Chloroform below0.20mg/L

Dibromochloromethane below0.10mg/L

* Foreffectivedisinfection,thereshouldbearesidualconcentrationoffreechlorineof0.5mg/L

afteratleast30mincontacttimeatpH<8.0


DBPformationcanbereducedthroughcost-effectivemethods,particularlybyreducingtheamount

ofnaturalorganicmaterialinwater(throughfiltrationorothermeans)priortodisinfection.WCCsup-

portsadoptionofthesemethodswheneverpossible.However,asWHOstronglycautions:

“The health risks from these byproducts at the levels at which they occur in drinking water

are extremely small in comparison with the risks associated with inadequate disinfection.

Thus, it is important that disinfection not be compromised in attempting to control such

byproducts.”

AstarkexampleoftheimportanceofwaterdisinfectionisthecholeraepidemicthatbeganinPeruin

1991,andspreadto19LatinAmericancountries.Inadequatedisinfectionofmunicipalwatersupplies

wasamajorfactorcontributingtothespreadoftheepidemicthatcausedmorethanonemillionill-

nessesand12,000deaths.Duringtheoutbreak,officialswiththePanAmericanHealthOrganization

reportedthatconcernsaboutpotentialhealthrisksfromdisinfectionbyproducts ledmunicipalities

andcommunitiesintheregiontoabandonchlorination.Oneofficiallaterwrote,“Ratherthanbeing

abatedby increaseuseofchlorination,thewaterbornetransmissionofcholerawasactuallyaided

becauseofworriesaboutchlorinationbyproducts.”

Chlorination does not harm aquatic environments

Chlorinateddrinkingwater is unlikely to beharmfulwhendischarged into aquatic environments.

AnextensiveriskassessmentconductedunderEuropeanUnionguidelinesexaminedpotentialharm

fromvariousprocessestomakedrinkingwaterusingsodiumhypochlorite.Thisassessmentfoundno

significantenvironmentalrisksfromchlorineorbyproductsformedduringdrinkingwaterchlorina-

tion.TheDBPsformedindrinkingwaterdependonthenatureandquantityoforganicmatterpresent

aswellasonthedisinfectantandothertreatmentsused.Indrinkingwatertheprincipalbyproducts

aretrihalomethanes(THMs;mainlychloroform)andhaloaceticacids(HAAs),withsmalleramounts

ofotherbyproducts.Direct‘wholeeffluent’experimentsrepresentingvarioususes,includingdrink-

ingwater, have shown that no significant amounts of persistent and potentially bioaccumulative

substancesareformed.ToxicitytestsonthesemixturesdemonstratedthatthepresenceofDBPsdid

notincreasethetoxicity.

Amajorconcernfromthepastwastheformationofsomehighly-chlorinated,high-hazardmolecules,

suchasdioxins, resultingfromchlorineused inpaperpulpbleaching.However,dioxinswereonly

formedfrom‘activechlorine’underspecificconditions:acidpHandinthepresenceofcertainphe-

nolssuchasthoseabundantinthelignincomponentofwood.Thereisnosignificantformationof

dioxinsorotherhigh-hazardmoleculesatneutraloralkalinepH.Allcurrentusesof‘activechlorine’

formicrobialcontrolandcleaningtakeplaceatalkalineorneutralpH.


Disinfection technologies must be effective, affordable and appropriate for local conditions

Various technologies are available

Chlorinationisthemostwidelyuseddisinfectant,bothincentralizedwaterdistributionsystemsand

for point-of use treatment in individual households. Its effectiveness against awide spectrumof

disease-causingorganisms,relativelylowcostandhighreliabilitycontributetoitspopularity.

Chlorineisappliedtowatereitheraselementalchlorine(chlorinegas),orthroughtheuseofchlorin-

atingchemicalssuchascalciumhypochlorite(tabletsorgranules)orsolutionsofsodiumhypochlorite

(liquidbleach).While varying in formandconcentration,eachproduces“free chlorine” toattack

germsinwater.Theleveloffreechlorinecanbeeasilymonitored,providinganimportantmeasureof

waterquality.A“residual”levelofchlorinehelpsprotecttreatedwatertreatedwaterinthedistribu-

tionsystem,particularlyimportantforolderwatersystems.

Anumberofalternativemethodsareavailablefordrinkingwaterdisinfection.Theseinclude:ozone,

apowerfuldisinfectingagentgeneratedbypassingoxygenordryairthroughasystemofhighvolt-

ageelectrodes;chlorinedioxide,apowerfulchemicalthatcontainschlorinemolecules,butdisinfects

through a differentmechanism than free chlorine; and ultraviolet (UV) radiation, a non-chemical

methodtodisinfectwaterusinglightgeneratedbyspeciallamps.Inaddition,someharmfulmicro-

organismscanberemovedfromwaterthoughfiltrationorotherphysicalmeans.Filtrationmethods

rangefromsimplesandfiltersforhouseholdtreatment,toreverseosmosissystemsinstate-of-the-art

treatmentplants.

Eachdisinfectiontechnologyhasuniquestrengthsandlimitations.Nosingledisinfectionmethodis

rightforallcircumstances,andinfact,amulti-stepprocessmaybeappropriatetomeetoveralltreat-

mentgoals.


Considerations for selecting disinfection methods

Efficacy against pathogens—Controllingmicrobialcontaminationmustalways

begivenprimaryimportance.Whilechlorineiseffectiveagainstmostpathogens,

additional treatment stepsmay be neededwhere resistant organisms such as

Cryptosporidium or Giardiaareaconcern.

Laws and regulations—Treatmentprocessesandfinaldrinkingwaterqualitymust

meetlocalstandards.

Source water quality—Thecharacteristicsoflocalsourcewater,suchasturbidity

andorganicload,willimpactdisinfectionrequirements.

Residual protection—Onlychlorine-basedproductsprovidea“residual”levelof

disinfectantthatremainsinwatertopreventmicrobialre-growthandhelppro-

tecttreatedwaterduringdistributionandstorage.Therefore,nootherdisinfec-

tionmethodbyitselfcanprotectwaterallthewaytothetap.

Local capacity—Sufficient resources, suppliesandtrainingmustbeavailable to

maintainserviceaftertreatmenttechnologiesareadopted.

Safety—Alldisinfectionchemicalsrequireproperstorageandhandlingpractices.

Safetyguidelinesareavailablefromnationalandregionalchlorineassociations.

Consumer expectations—Educationaleffortsmayhelplocalcommunitiesunder-

stand the need for water disinfection, and ensure acceptance of treatment

methods.

Affordability—Waterserviceand/orhometreatmentproductsmustbeaffordable

toconsumers.

[email protected]

WCCmembers

Producer AssociationsAsociacionNacionaldelaIndustriaQuimica(Mexico)

www.aniq.org.mx/

CanadianChlorineChemistryCouncil

www.cfour.org

ChlorineChemistryDivisionoftheAmericanChemistry

Council

www.americanchemistry.com/chlorine

ChlorineInstitute

www.cl2.com

Clorosur

www.clorosur.org

EuroChlor

www.eurochlor.org

IndianChemicalManufacturersAssociation

JapanSodaIndustryAssociation

www.jsia.gr.jp

KoreaChlor-AlkaliAssociation

PlasticsandChemicalsIndustriesAssociationofAustralia

www.pacia.org.au

Taiwan(China)Acid&AlkaliIndustryAssociation

Product Sector AssociationsAsia-PacificVinylNetwork

EuropeanCouncilofVinylManufacturers

www.ecvm.org

HalogenatedSolventsIndustryAlliance

www.hsia.org

VinylCouncilofAustralia

www.vinyl.org.au

VinylCouncilofCanada

www.plastics.ca/vinyl

VinylEnvironmentalCouncil(Japan)

www.vec.gr.jp

VinylInstitute

www.vinylinfo.org

Corresponding AssociationsRusChlor,theRussianchlor-alkaliassociation

ChinaChlor-AlkaliIndustryAssociation[pending]

drinking water chlorination - world chlorine council · 2 drinking water chlorination • world...

Documents