Shower-BasedWaterSavings
FlowRatevs.Durationvs.
Volume
AnIndependentMaPResearchReport
January2017
Authors
BillGauley,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
HOWSHOWERHEADFLOWRATESIMPACT
SHOWERDURATIONANDVOLUME
1.0
Introduction
TwoofthemostimportantresidentialwaterdemandstudiesinNorthAmericaarethe1999and
2016ResidentialEndUsesofWaterStudies(REUS1999andREUS2016)completedbyAquacraft,
Inc.1Thesetwostudiesdataloggedwateruseinalargenumberofsingle-familyhomes2across
the USA and Canada to quantify the volume associated with each individual water use within
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 and many less frequently, and many take longer showers and many take shorter
showers–but,onaverage,wetakeabout0.69showersperdaywithadurationofabout7.8
minutespershower.
1
WhileREUSreportswerepublishedin1999and2016,waterdemanddatawerecollectedintheyearspreceding
publication.
2
1,187homeswereloggedin1999and762homeswereloggedin2016.
3WaterResearchFoundation’s1999ResidentialEndUsesofWater(Mayeretal.1999),
http://www.waterrf.org/PublicReportLibrary/RFR90781_1999_241A.pdf
4WaterResearchFoundation’s2016ResidentialEndUsesofWaterStudyUpdate–Version2(Mayeretal.2016),
http://www.waterrf.org/Pages/Projects.aspx?PID=4309)
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Whileshoweringaccountsforalmostone-fifthofindoorresidentialwaterdemands,thereare
challengesassociatedwithreducingshower-basedwaterdemandsthatdonotexistfortoiletbased 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 feel of the water striking the skin. Showering is a very personal experience and
product manufacturers have responded by designing many hundreds of different models of
showerheads, each with slightly different spray characteristics. Some showerheads are handheld, while some are wall-mounted; some are very high-flow, while some are super efficient;
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 any way 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,
homeownersthatarenotfullysatisfiedwiththeir“showerexperience”(forwhateverreason)
caneasilyreplacetheiroffendingfixtureforamoreacceptableone.
This ‘ease of installation’ is the crux of the challenge faced by water utilities and showerhead
manufacturerstryingtoreducecustomerwaterdemandsandachieveproductefficiency.For
example, while it is relatively inexpensive for a utility to give away or rebate the purchase of
efficientshowerheadsbytheircustomers,anditisrelativelyeasyforahomeownertoinstallan
efficient showerhead (usually without the need to hire a plumber), it is just as easy for a
homeowner to remove the new showerhead if they are not happy with its performance and
replace it with a potentially high-flow-rate model, eliminating any expected water or energy
savings. Perhaps this is why a quick web search indicates there are far fewer water utilities
rebatingorgivingawayefficientshowerheadsnowthantherewasadecadeago.
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Figure1
Asillustrated above, between 1999 and 2016, shower-based water demands declined by only
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.
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AverageShowerheadFlowRates–REUS1999vs.REUS2016
AcomprehensiveanalysiswascompletedbyGauley/Koelleronshower-baseddatacollectedas
part of the 1999 and 2016 Residential End Use Studies.5 The analysis first looked at average
showerheadflowrates6.Onlyflowratesbetween1.0and4.0gallonsperminute(gpm)were
consideredintheanalysisasapproximately97%oftheshower-basedeventsidentifiedbythe
Trace Wizard program used by Aquacraft, Inc. fell within this flow rate range7and there was
some uncertainty if all events with very high or very low flow rates were truly shower-based
events.
TheGauley/Koelleranalysisgroupedtheapproximately42,500showereventsrecordedinthe
REUS1999 and the approximately 15,500 shower events recorded in the REUS2016 into
increments of 0.2 gallons per minute (gpm), based on 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%ofinstalledshowerheadshadflow
ratesof2.0gpm(themaximumflowrateforaWaterSense®labeledshowerhead)orlesswhile
by2016thisratehadincreasedto56%.Notethatifonlyshowerheadswithflowratesof2.0
gpmorlessareconsidered“efficient”,then(atleastasof2016)approximately44%ofinstalled
showerheadscontinuetooperateinefficiently.
Theresultsofthisanalysisindicatethatshowerheadtechnology(atleastinsofarasflowrates
areconcerned)hasimprovedbetween1999and2016.SowhydidtheREUstudiesidentifyso
5
Shower-baseddatafromtheResidentialEndUsesofWaterstudieswereprovidedbyCo-PrincipalInvestigator,
PeterMayer,P.E.
6
TheREUSstudiesrecordedactualflowrates,notratedflowrates.
7
Waterdemanddatacollectedaspartofthe1999and2016REUSareanalyzedusingtheTraceWizardsoftware
program.Thisprogramusestheflowrateandflowdurationofeachrecordedwateruseeventtoassigntheevent
totheappropriatehouseholdfixtureorappliance.WhiletheaccuracyoftheTraceWizardanalysisisconsidered
veryhigh,itisnotconsideredperfect.ForafulldescriptionoftheTraceWizardprogrampleasesee
http://www.aquacraft.com/downloads/trace-wizard-description/
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littleshower-basedwatersavingsbetween1999and2016?Thelowlevelofsavingscouldbe
explainedifpeopledo,onaverage,compensateforlowerflowratesbytakinglongerduration
showers.Butisthisreallythecase?
Figure2
3.0
ShowerFlowRatevs.Durationvs.Volume
Theprimarypurposeofthisstudywastoverifyifthereisatendencyforshowerdurationsto
increaseasflowratesdecrease,possiblyresultinginlittleornowatersavingsassociatedwith
the use of lower flow rate showerheads. An analysis was completed on the 1999 and 2016
REUSdatatodeterminetherelationshipbetweenshowerflowrateandduration(notethatflow
ratemultipliedbydurationequalsshowervolume).
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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.
Figure3
WhilewaterdemanddataforthetwoREUstudieswerecollectedmorethan15yearsapartand
there was some variation in the participating communities, the results of the flow rate vs.
durationanalysisprovedtoberemarkablysimilarforthetwodatasets.Forexample,Figure3
illustrates the relationship between shower flow rate vs. shower duration vs. shower volume.
Note that shower duration increases only minimally as flow rates decrease for both the 1999
and2016datasets,atleastforflowratesbetween1.0and4.0gallonsperminute.Forevery
8
Whilesomepeoplemaypurposelychoosetoinstallverylowflowrateshowerheads,itisprobablethatthelowflowrates
recordedinsomeoftheparticipatinghomesweretheresultoflowwaterpressuresand/orexcessivemineralbuildupinthe
watersupplypipingorshowerhead,ratherthanasaconsequenceofshowerheaddesign.
9
Thisrangeincluded96%ofallshowereventsandexcludedeventsthatmayhavebeenmisidentifiedasshowersbytheTrace
Wizardsoftware,e.g.,eventswithdurationsaslowas10secondsorashighas173minutes.
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0.2 gallon per minute decrease in flow rate, the average shower duration increases by only 8
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 their own unique routine for showering regardless of the flow
rate of the showerhead. In fact, it is possible that the few extra seconds spent showering at
lowerflowratesmaybeprimarilyrelatedtowashingandrinsinghair.
Sowhyweretheshower-basedsavingsidentifiedinthe2016REUSsolow?Partoftheanswer
may be in how the results are presented. While, for simplicity sake, tables in the 2016 REUS
report identify average per capita per shower water demands of 11.6 gallons for 1999 and of
11.1 gallons for 2016, these values, by themselves, do not articulate the margin of error
associated with their calculation. Figure 4 (reproduced from Figure 6.13 in REUS2016) 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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SummaryandConclusion
Theflowrateanalysis(resultsillustratedinFigure2)identifiedahigherpercentageofinstalled
lowflowrateshowerheadsin2016thanin1999.
The flow rate vs. duration analysis indicated that people tend to only marginally 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.
Water utilities interested in achieving higher levels of water savings should be encouraged to
consider(orre-consider)promotingorrebatinghigh-performancelowflowrateshowerheads.
Pleasesendanyquestionsyoumayhaveregardingthecontentofthisreporttotheauthors:
BillGauley,P.Eng.,Principal,GauleyAssociatesLtd.,[email protected]
JohnKoeller,P.E.,Principal,Koeller&Company,[email protected]
NOTE:TheauthorswouldliketothanktheWaterResearchFoundationfortheirsupportof
theResidentialEndUsesofWaterstudiesandPeterMayer,P.E.,Principal,WaterDM,forhis
consultationandpeerreviewofthiswork.
10
High-EfficiencyShowerheadPerformanceStudy,2009,Gauley,Robinson,Elton.Reportcanbefoundat:http://www.maptesting.com/assets/files/Veritec-Waterloo%20Final%20Report%20Dec%202009%20copy.pdf
9
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