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Shower-BasedWaterSavings
FlowRatevs.Durationvs.Volume
AnIndependentMaPResearchReport
January2017
AuthorsBillGauley,P.Eng.,Principal,GauleyAssociatesLtd.JohnKoeller,P.E.,Principal,Koeller&Company
TABLEOFCONTENTS
1.0 Introduction..................................................................................................................................1
2.0 AverageShowerheadFlowRates–REUS1999vs.REUS2016......................................4
3.0 ShowerFlowRatevs.Durationvs.Volume........................................................................5
4.0 SummaryandConclusion.........................................................................................................9
FIGURES
Figure1-AverageDailyIndoorPerCapitaWaterUseREUS1999andREUS2016
Figure2–1999REUSvs.2016REUSPercentageFlowRates
Figure3–ShowerFlowRatevs.Durationvs.Volume,1999REUSvs.2016REUS
Figure4–AverageDailyIndoorPerCapitaWaterUsewith95%ConfidenceErrorBars
January2017 Gauley/Koeller:www.map-testing.com
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HOWSHOWERHEADFLOWRATESIMPACTSHOWERDURATIONANDVOLUME
1.0 Introduction
TwoofthemostimportantresidentialwaterdemandstudiesinNorthAmericaarethe1999and
2016ResidentialEndUsesofWaterStudies(REUS1999andREUS2016)completedbyAquacraft,
Inc.1Thesetwostudiesdataloggedwateruseinalargenumberofsingle-familyhomes2across
theUSAandCanada toquantify thevolumeassociatedwitheach individualwaterusewithin
thehome.
The1999report3identifiedanaverageindoorwaterdemandof69.3gallonspercapitaperday
(gpd).By2016,thisdemandhadfallento58.6gcd–adeclineofabout10.7gcdover16years
oranaverageofabout1%peryear4.Whatseemsremarkableisthatafull90%ofthisreduction
wasattributedtoonlytwohouseholdusecategories-toiletdemandsdeclinedby4.3gcdand
clotheswasherdemandsdeclinedby5.4gcd(seeFigure1reproducedfrom2016REUS).
Sowhysolittlesavingsassociatedwithshowers?
The 2016 REUS determined that showering currently accounts for about 19% of indoor
residentialwaterdemands;thatpeopletakeanaverageof0.69showersperday;andthatthe
average shower duration is about 7.8 minutes long. Of course, many people shower more
frequently andmany less frequently, andmany take longer showers andmany take shorter
showers–but,onaverage,wetakeabout0.69showersperdaywithadurationofabout7.8
minutespershower.
1WhileREUSreportswerepublishedin1999and2016,waterdemanddatawerecollectedintheyearsprecedingpublication.21,187homeswereloggedin1999and762homeswereloggedin2016.3WaterResearchFoundation’s1999ResidentialEndUsesofWater(Mayeretal.1999),http://www.waterrf.org/PublicReportLibrary/RFR90781_1999_241A.pdf4WaterResearchFoundation’s2016ResidentialEndUsesofWaterStudyUpdate–Version2(Mayeretal.2016),http://www.waterrf.org/Pages/Projects.aspx?PID=4309)
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Whileshoweringaccountsforalmostone-fifthof indoorresidentialwaterdemands,thereare
challengesassociatedwithreducingshower-basedwaterdemandsthatdonotexist fortoilet-
based and clothes washer-based demands – namely, the personal and tactile experience
associatedwithshowering,i.e.,end-userbehavior.Althoughtheprimaryreasonforshowering
may be to “get clean”, many people enjoy the experience of showering – the warmth, the
comfort, the feelof thewater striking theskin. Showering isaverypersonalexperienceand
product manufacturers have responded by designing many hundreds of different models of
showerheads,eachwithslightlydifferentspraycharacteristics. Someshowerheadsarehand-
held,while somearewall-mounted; someareveryhigh-flow,while someare superefficient;
some provide high-velocity sprays, while some feel like a gentle rain shower; some offer a
numberofdifferentspraypatterns,whilesomearestrictlyutilitarian,etc.Inshort,peoplecan
customize their shower ‘experience’ almost anyway they choose. However, because of the
significant impact of personal preference on showerhead selection, in an unfettered
marketplaceitislikelythatmanypeoplewouldchoosetoinstallhighflowrateshowerheads–
sacrificingwaterandenergyefficiencyforcomfort. What’smore,showerheadstendtobefar
less expensive than clothes washers or toilets, and much easier to change-out. That is,
homeownersthatarenot fullysatisfiedwiththeir“showerexperience”(forwhateverreason)
caneasilyreplacetheiroffendingfixtureforamoreacceptableone.
This ‘easeof installation’ is thecruxof thechallenge facedbywaterutilitiesandshowerhead
manufacturerstryingtoreducecustomerwaterdemandsandachieveproductefficiency.For
example,while it is relatively inexpensive forautility togiveawayor rebate thepurchaseof
efficientshowerheadsbytheircustomers,anditisrelativelyeasyforahomeownertoinstallan
efficient showerhead (usually without the need to hire a plumber), it is just as easy for a
homeowner to remove thenew showerhead if they are not happywith its performance and
replace it with a potentially high-flow-ratemodel, eliminating any expectedwater or energy
savings. Perhaps this iswhy a quickweb search indicates there are far fewerwater utilities
rebatingorgivingawayefficientshowerheadsnowthantherewasadecadeago.
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As illustratedabove,between1999and2016,shower-basedwaterdemandsdeclinedbyonly
0.5gcd!Thereseemstobetwosimplepossibilitiesforthislowlevelofsavings-either:
a) showerheadtechnology(andefficiency)didnotimprovesignificantlybetween1999and
2016,OR
b) asshowerheadsbecamemoreefficient(i.e.,withlowerflowrates),peoplecompensated
by taking longer showers, thus negating the potential water savings associated with
thoselowerflowrates.
Butthereisalsoathirdpossibility–thatactualshowerheadsavingsaregreaterthanthat
indicatedinFigure1,andthispossibilityisdiscussedinSection4.
Figure1
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2.0 AverageShowerheadFlowRates–REUS1999vs.REUS2016
AcomprehensiveanalysiswascompletedbyGauley/Koelleronshower-baseddatacollectedas
part of the1999 and2016Residential EndUse Studies.5 The analysis first looked at average
showerheadflowrates6. Onlyflowratesbetween1.0and4.0gallonsperminute(gpm)were
considered intheanalysisasapproximately97%oftheshower-basedevents identifiedbythe
TraceWizard programusedbyAquacraft, Inc. fellwithin this flow rate range7and therewas
someuncertainty if all eventswith veryhighor very low flow rateswere truly shower-based
events.
TheGauley/Koelleranalysisgroupedtheapproximately42,500showereventsrecorded inthe
REUS1999 and the approximately 15,500 shower events recorded in the REUS2016 into
incrementsof0.2 gallonsperminute (gpm),basedon their average flow rate. From this, the
percentage of shower events that occurred in each flow rate increment for each of the two
studies(Figure2)wascalculated.
The analysis clearly shows a trend towards lower flow rate showerheads between 1999 and
2016. Forexample,the1999dataidentifiedthatonly44%of installedshowerheadshadflow
ratesof2.0gpm(themaximumflowrateforaWaterSense®labeledshowerhead)orlesswhile
by2016thisratehadincreasedto56%. Notethat ifonlyshowerheadswithflowratesof2.0
gpmorlessareconsidered“efficient”,then(atleastasof2016)approximately44%ofinstalled
showerheadscontinuetooperateinefficiently.
Theresultsofthisanalysis indicatethatshowerheadtechnology(at least insofarasflowrates
areconcerned)hasimprovedbetween1999and2016.SowhydidtheREUstudiesidentifyso
5Shower-baseddatafromtheResidentialEndUsesofWaterstudieswereprovidedbyCo-PrincipalInvestigator,PeterMayer,P.E.6TheREUSstudiesrecordedactualflowrates,notratedflowrates.7Waterdemanddatacollectedaspartofthe1999and2016REUSareanalyzedusingtheTraceWizardsoftwareprogram.Thisprogramusestheflowrateandflowdurationofeachrecordedwateruseeventtoassigntheeventtotheappropriatehouseholdfixtureorappliance.WhiletheaccuracyoftheTraceWizardanalysisisconsideredveryhigh,itisnotconsideredperfect.ForafulldescriptionoftheTraceWizardprogrampleaseseehttp://www.aquacraft.com/downloads/trace-wizard-description/
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littleshower-basedwatersavingsbetween1999and2016?Thelowlevelofsavingscouldbe
explainedifpeopledo,onaverage,compensateforlowerflowratesbytakinglongerduration
showers.Butisthisreallythecase?
3.0 ShowerFlowRatevs.Durationvs.Volume
Theprimarypurposeofthisstudywastoverify ifthere isatendencyforshowerdurationsto
increaseasflowratesdecrease,possiblyresulting in littleornowatersavingsassociatedwith
the use of lower flow rate showerheads. An analysiswas completed on the 1999 and 2016
REUSdatatodeterminetherelationshipbetweenshowerflowrateandduration(notethatflow
ratemultipliedbydurationequalsshowervolume).
Figure2
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Forreasonsstatedearlier,onlyflowratesbetween1.0and4.0gallonsperminute(gpm)were
included in the analysis8. For similar reasons, only shower durations between 2.0 and 20.0
minuteswereincludedintheanalysis9.
WhilewaterdemanddataforthetwoREUstudieswerecollectedmorethan15yearsapartand
there was some variation in the participating communities, the results of the flow rate vs.
durationanalysisprovedtoberemarkablysimilarforthetwodatasets.Forexample,Figure3
illustrates the relationshipbetweenshower flowratevs. showerdurationvs. showervolume.
Note that showerduration increasesonlyminimallyas flowratesdecrease forboth the1999
and2016datasets,at leastforflowratesbetween1.0and4.0gallonsperminute. Forevery
8Whilesomepeoplemaypurposelychoosetoinstallverylowflowrateshowerheads,itisprobablethatthelowflowratesrecordedinsomeoftheparticipatinghomesweretheresultoflowwaterpressuresand/orexcessivemineralbuildupinthewatersupplypipingorshowerhead,ratherthanasaconsequenceofshowerheaddesign.9Thisrangeincluded96%ofallshowereventsandexcludedeventsthatmayhavebeenmisidentifiedasshowersbytheTraceWizardsoftware,e.g.,eventswithdurationsaslowas10secondsorashighas173minutes.
Figure3
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0.2gallonperminutedecrease in flowrate, theaverageshowerduration increasesbyonly8
secondsbasedon1999dataandbyonly2secondsbasedon2016data.Bothsetsofdataalso
showadecreaseinshowervolumeastheflowratedecreases.Forevery0.2gallonperminute
decreaseinflowrate,theaverageshowervolumedecreasesby1.24gallonsbasedon1999data
andby1.44gallonsbasedonthe2016data.
Figure3clearlyillustratesthat,onaverage:
• people do not compensate for lower flow rates by commensurately increasing the
durationoftheirshower,and
• lowerflowrateshowerheadsdoresultinaloweroverallshowervolume.
While some people take longer showers and some take shorter showers, the data shows, in
general,people tend to follow theirownunique routine for showering regardlessof the flow
rateof the showerhead. In fact, it ispossible that the fewextra seconds spent showeringat
lowerflowratesmaybeprimarilyrelatedtowashingandrinsinghair.
Sowhyweretheshower-basedsavingsidentifiedinthe2016REUSsolow?Partoftheanswer
maybe inhowthe resultsarepresented. While, for simplicity sake, tables in the2016REUS
report identifyaveragepercapitapershowerwaterdemandsof11.6gallons for1999andof
11.1 gallons for 2016, these values, by themselves, do not articulate the margin of error
associatedwith their calculation. Figure4 (reproduced fromFigure6.13 inREUS2016) shows
theaveragedailypercapitademandsforeachindooruseaswellasthemarginoferroratthe
95%confidencelevel.Assuch,whileaverageshower-baseddemandsin1999areidentifiedas
11.6gcd,thevalue(atthe95%confidencelevel)couldactuallyrangefromaslittleasabout11.2
gcdtoashighas12.0gcd,while2016shower-baseddemandscouldrangefromabout10.5to
11.7gcd.Basedonthisanalysis,averagedailyper-showerdemandscouldactuallybeasmuch
as0.5gallonshigherin2016orasmuchas1.5gallonslowerin2016.
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Figure4
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4.0 SummaryandConclusion
Theflowrateanalysis(resultsillustratedinFigure2)identifiedahigherpercentageofinstalled
lowflowrateshowerheadsin2016thanin1999.
The flow ratevs.durationanalysis indicated thatpeople tend toonlymarginally increase the
durationoftheirshowertocompensateforlowerflowrates.
Basedonapplyinga95%confidenceintervaltopercapitashower-baseddemands,itispossible
that the average 0.5 gallons per capita per day shower savings between 1999 and 2016 (as
identifiedinthe2016REUSreport),maybesomewhatunder-reportedandmayactuallybeas
highas1.5gallonspercapitaperday.
While studies have shown that people tend to prefer higher flow rate showerheads10, the
resultsofthisanalysisclearlyshowthatwatersavingscanbeachievedbyusinglowerflowrate
showerheads. As such, it appears that low flow rate showerheads that meet customers’
expectationforperformancewillprovidethebestopportunitytomaximizewatersavings.
Waterutilities interested inachievinghigher levelsofwater savings shouldbeencouraged to
consider(orre-consider)promotingorrebatinghigh-performancelowflowrateshowerheads.
Pleasesendanyquestionsyoumayhaveregardingthecontentofthisreporttotheauthors:
BillGauley,P.Eng.,Principal,GauleyAssociatesLtd.,bill@gauley.ca
JohnKoeller,P.E.,Principal,Koeller&Company,koeller@earthlink.net
NOTE:TheauthorswouldliketothanktheWaterResearchFoundationfortheirsupportof
theResidentialEndUsesofWaterstudiesandPeterMayer,P.E.,Principal,WaterDM,forhis
consultationandpeerreviewofthiswork.10High-EfficiencyShowerheadPerformanceStudy,2009,Gauley,Robinson,Elton.Reportcanbefoundat:http://www.map-testing.com/assets/files/Veritec-Waterloo%20Final%20Report%20Dec%202009%20copy.pdf
TABLEOFCONTENTS
1.0 Introduction..................................................................................................................................1
2.0 AverageShowerheadFlowRates–REUS1999vs.REUS2016......................................4
3.0 ShowerFlowRatevs.Durationvs.Volume........................................................................5
4.0 SummaryandConclusion.........................................................................................................9
FIGURES
Figure1-AverageDailyIndoorPerCapitaWaterUseREUS1999andREUS2016
Figure2–1999REUSvs.2016REUSPercentageFlowRates
Figure3–ShowerFlowRatevs.Durationvs.Volume,1999REUSvs.2016REUS
Figure4–AverageDailyIndoorPerCapitaWaterUsewith95%ConfidenceErrorBars
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