This article was downloaded by: [American University of Beirut]On: 17 September 2014, At: 16:17Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Urban Water JournalPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/nurw20

Experimental investigation on water saving by thereuse of washbasin grey water for toilet flushingA. Campisano a & C. Modica aa Department of Civil and Environmental Engineering , University of Catania , Viale A. Doria6, 95125 Catania, ItalyPublished online: 24 Feb 2010.

To cite this article: A. Campisano & C. Modica (2010) Experimental investigation on water saving by the reuse of washbasingrey water for toilet flushing, Urban Water Journal, 7:1, 17-24, DOI: 10.1080/15730621003596739

To link to this article: http://dx.doi.org/10.1080/15730621003596739

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

RESEARCH ARTICLE

Experimental investigation on water saving by the reuse of washbasin grey water for toilet flushing

A. Campisano* and C. Modica

Department of Civil and Environmental Engineering, University of Catania, Viale A. Doria 6, 95125 Catania, Italy

(Received 17 November 2008; final version received 10 November 2009)

The paper presents the results of an experimental investigation aimed at estimating the water saving obtained byreusing washbasin grey waters for toilet flushing in domestic bathrooms. Six Italian households characterised bydifferent number of users largely heterogeneous in age, gender, occupation and customs were selected for theexperimental campaign. Washbasin and toilet uses for each selected household were monitored recordingchronological series of time instants of washbasin tap opening/closure and of toilet flushing operations. On the basisof water balances on a short time scale, acquired data enabled the evaluation of water saving and unused grey waterderiving by the adoption of a simple grey water reuse scheme. Specific dimensionless variables were adopted topresent the results and to enable their use within the ranges of practical applications.

Keywords: greywater; reuse scheme; toilet; washbasin; water saving

Introduction

As it is largely recognised, today, high-quality watersshould be primarily used for drinking purposes, while,for other civil uses, waters with less valuable qualitycharacteristics, such as grey waters, should be takeninto account (Vickers 2001; USEPA 2004).

However, while healthy and environmental impactsof the reuse of municipal wastewater are oftenregulated by guidelines released by national govern-ments, today there are very few regulations whichspecifically concern grey water recycling (Li et al.2009). Also in Italy, national regulations on the reuseof municipal wastewaters for agricultural, civil andindustrial purposes have been recently released by theMinistry of the Environment (D.M. 185/2003). How-ever, these regulations focus on large-scale (municipal)wastewater reuse, without making explicit reference toon-site grey water reuse for indoor applications.

Since the beginning of the sixties, various schemesand systems for domestic grey water reuse have beenproposed by many authors (McDonald et al. 1993;Aylward et al. 2006). However, these schemes have notbeen largely implemented due to the high costs neededfor significantly restructuring the house hydraulicpiping systems (Jefferson et al. 1999; Brennan andPatterson 2004). In fact, a large part of these schemesrequires the building of specific separate pipingnetworks for collecting grey waters coming fromshowers, washbasins, washing-machines, dishwashers

and other household water facilities, sometimes addingalso rain water from the roofs. These systems also needto be equipped with high-volume tanks for the greywater storage adding problems related to the need oflarge installation space and to the grey water qualitydegradation for the high detention times within thetank (Maeda et al. 1996; Dixon et al. 1999; Eriksson2002).

During the recent years, different investigations(Eriksson 2002; Failla and Stante 2004) looked into theanalysis of water uses in urban households and theevaluation of water saving by grey and rain waterreuse. Results of these investigations showed that theprompt reuse of grey waters could be applied to theflushing of toilets. In particular, available literaturedata (Butler et al. 1995; Christova-Boal et al. 1996;Surendran and Weatley 1998; Mukhopadhyay et al.2001; Lazarova et al. 2003) shows that a significantpart (close to 30%) of water in houses is actually usedfor toilet flushing and that values between 10 and 15%of the domestic total consumption are related to theuse of bathroom washbasins for personal hygiene.These percentages show low variability in examinedliterature.

From a qualitative viewpoint, it has been shown(Friedler 2004) that washbasin grey waters result lesspolluted in comparison to those from other domesticsources like kitchen sinks, washing machines, dish-washers, etc.

*Corresponding author. Email: acampisa@dica.unict.it

Urban Water Journal

Vol. 7, No. 1, February 2010, 17–24

ISSN 1573-062X print/ISSN 1744-9006 online

� 2010 Taylor & Francis

DOI: 10.1080/15730621003596739

http://www.informaworld.com

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

Previous considerations suggest possible significantbenefits deriving from on-site reuse of grey waters bythe direct hydraulic connection of washbasin and toiletdevices.

Investigations concerning washbasin and toiletwater consumption data are characterised by largetemporal scales (monthly or quarterly acquisition).Instead, the availability of data on a short time scaleis very scarce, notwithstanding the important infor-mation that these data can provide; detailed chrono-logical series of washbasin and toilet waterconsumption, in fact, can enable accurate evaluationof water saving by grey water reuse, taking intoaccount also the technical characteristics of theadopted reuse installation (i.e. toilet cistern volume,grey water tank volume, etc.).

In this paper the results of an experimentalinvestigation aimed at acquiring short time scalechronological series of water uses of washbasins andtoilets in domestic bathrooms are presented. For theexperimental campaign, six households characterisedby heterogeneous users were chosen. On the basis ofwater balances on a short time scale, the acquired dataseries were used to evaluate the water saving that canbe obtained with a simple grey water reuse scheme. Inthe adopted scheme, the water used at the washbasin isstored into a grey water tank and is then pumped up tothe toilet cistern in order to reduce the consumption ofdrinking water for toilet flushing.

Experimental activities

Household selection

In order to take into account different water usepatterns at washbasins and toilets, six householdscharacterised by various number of users largely

heterogeneous for age, gender, occupation and cus-toms were selected for the experiments. The selectedcases can be considered as quite representative ofseveral Italian types of urban households.

The main characteristics of the six households aresummarized in Table 1.

Experimental set-up

For each household a 2-week long measuring cam-paign was launched. This time length was consideredto be sufficient for determining the household wateruse patterns at washbasins and toilets (i.e. frequencyand duration of use, daily averages, etc.). Themonitoring campaign was developed in the periodfrom 27 March 2006 to 17 May 2006. The relativelyshort duration of the monitoring period and the almostconstant climatic conditions during the campaign wereconsidered to assure the homogeneity of measurementsamong the different households. The acquisition ofdata concerning uses of washbasins and toilets wascarried out using monitoring devices which werespecifically set-up for this experimental investigation.In particular, two simple electric sensors respectivelyconnected to the washbasin tap and to the push-buttonof the toilet cistern were adopted, the two sensorsbeing equipped with a data acquisition system (loggerSeries HOBO U-11).

For each household, the monitoring devicesallowed to record the time instants of the washbasintap openings/closures and the initial time instant of thetoilet flushing operation with the accuracy of 1 s.

Previously to the start-up of the experimentalcampaign, the described monitoring system was testedfor a time period of ten consecutive days in order tocheck eventual malfunctioning of the devices.

Table 1. Main characteristics of the six households selected for the experiments.

Household 1 Household 2 Household 3 Household 4 Household 5 Household 6

Type Shared house Family Family Family Family FamilyNumber of users 5 3 3 3 5 6Typology of users 5 students 2 retirees 1 student 1 employee

1 housewife1 student

2 retirees1 student

4 employees1 housewife

3 employees3 children

Users in week-days 5 2 3 2 5 6Users in week-end 1 3 3 3 5 6Measuring starting time 27 March 06

hour 23:0027 March 06hour 6:00

15 April 06hour 7:00

16 April 06hour 21:40

01 May 06hour 19:30

03 May 06hour 14:30

Measuring end time 10 April 06hour 23:00

10 April 06hour 6:00

29 April 06hour 7:00

30 April 06hour 21:40

15 May 06hour 19:30

17 May 06hour 14:30

Notes * ** *** None None ****

*No one at home during the week-end 1/2 April 2006.

**No one at home Thursday 6 April 2006.

***Four people during the period 21–28 April 2006.

****In the bathroom there are two washbasins, both monitored.

18 A. Campisano and C. Modica

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

Recorded data

Acquired data consisted of the chronological series ofchanges of state recorded by the two sensors. Recordedseries allow to determine the time period Dt of each useat washbasins. In Figure 1, for each one of the sixmonitored households, the cumulated curves (percapita) of toilet flush events N and of time periods ofwashbasin uses T ¼ SDt (s) are plotted for the entiretwo-week experimental time length.

Quasi-linear trends were found for all the cumu-lated curves pointing out uniform uses during themonitoring periods, then confirming that the campaignduration was sufficiently long.

Appreciably different patterns were found in therecorded data at the various examined households. Thehighest values were obtained for household 3 (inparticular with reference to T), whereas the lowestvalues were found for household 6 (with particularreference to N). These differences can be ascribed toseveral reasons related to the age and habits of users(older people flush the toilet more often, young

children use the washbasin and the toilet less), theirreal presence at home during the day, etc.

Obtained measurements allowed to calculatedaily averages �N and �T of N and T respectively foreach household (Table 2). These values resultedcomparable with those found in the literature (Blokker2006).

Evaluation of water saving

Water balances at daily scale

A preliminary evaluation of the convenience of reusingwashbasin grey waters for the flushing of toilets can beobtained by simply comparing daily total volumes atthe two devices evaluated on the basis of �N and �Tvalues of each household. To perform such acomparison, different values of the washbasin tapdischarge QWB (l/s) and of the toilet cistern volumeVTC (l) are to be considered. In particular, the variablet� ¼ VTC

QWB(s), representing the time required to fill the

toilet cistern with the washbasin discharge, can betaken into account.

Figure 1. Cumulated per capita toilet flushes N and washbasin use times T for the six households.

Urban Water Journal 19

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

Accordingly, the ratio between the evaluated (percapita) volume at the washbasin VWB and the flushing(per capita) volume at the toilet VF can be derived foreach household i as:

VWB

VF

� �i

¼�T�N

� �i

1

t� ð1Þ

Values of VWB

VFclose to 1 preliminary indicate the

possibility of high water saving by reusing washbasingrey water for toilet flushing.

Water balance simulations on a short time scale

The previous evaluations do not take into account thetechnical characteristics of the reuse scheme; in fact,the grey water volumes that could be effectively reusedfor the toilet flushing can vary significantly dependingon toilet cistern volume, grey water tank volume andwashbasin tap flow discharge.

In order to take into account these characteristicsfor an improved evaluation of water saving benefits,elaborations have to be carried out by means of waterbalance simulations on a short time scale based on theacquired experimental data. For this purpose, a simplereuse system collecting washbasin waters into a greywater tank and then into the toilet cistern volume wasconsidered in the analysis. In particular, the scheme isbased on the storage of the used washbasin waterwithin the grey water tank and on its prompt pumpingup to the toilet flushing cistern, as soon as the storedvolume in the grey water tank results equal to the toiletcistern volume. Volumes overflowing the grey watertank were considered to be lost in the sewer system.For the toilet flushing, the schematized system is basedon the primary use of stored grey waters and, only inthe case that they result insufficient, on the recourse tothe water from the main. Basic chlorination in the tankis to be considered in order to avoid problems of greywater quality decay, especially due to organics andparticles (Winward et al. 2008). Drawbacks connectedto the accumulation of sediments in the grey watertank are minimized by the pumping operations.Instead, sediment accumulation in the toilet cistern isavoided by the frequent cistern rinses with drinkingwater occurring when grey water for toilet flushing isnot sufficient. Additional details on the adopted reuse

scheme with main technological aspects for thepractical set up are described in Campisano andModica (2008).

Simulations of water balances on a short time scalewere carried out separately for the data acquired fromeach household and water savingWS was evaluated as:

WS ¼ 1� VA

VF

� �� 100 ð2Þ

where VA is the (per capita) drinking water volumeused for flushing operations.

Water balances allowed to evaluate also the greywater losses GWL, i.e. unused grey water overflowedfrom the tank (directly to the sewer) as the tank is full:

GWL ¼ VO

VWB� 100 ð3Þ

where VO is the (per capita) water volume overflowedfrom the grey water tank.

Moreover, the dimensionless ratio R ¼ VGT

VTCbetween

the grey water tank volume VGT and the toilet cisternvolume VTC was adopted for a more general use of theresults.

Results and discussion

For the preliminary evaluation of water saving, dailywater balances were applied to the acquired experi-mental data. Equation (1) is plotted in the graph ofFigure 2 for the six households for a large range of t*.Measured values of t* for the households are evidencedby dots. The graph shows that obtained curves resultquite close one to each other, due to similar values ofratios

� �T�N

�iamong the various households (Table 2).

Furthermore, the graph shows that values oft* 5 60 s allow to reuse exclusively washbasin greywaters for the toilet flushing, i.e.

�VWB

VF

�i> 1. However,

considering standard toilet cisterns, these situations (asfor households 2 and 3) are not advisable since theobtained water saving would be achieved with a toohigh and wasteful discharge at the washbasin tap; inaddition, in these cases, the installation of dual-flushsystems could result to be not really useful. Differently,values of t* close to 120 s allow the possibility ofreusing the washbasin grey waters for about 50% of

Table 2. Values of �N, �T and �T/ �N for the six selected households.

Household 1 Household 2 Household 3 Household 4 Household 5 Household 6

�N 4.2 4.5 6.3 5.9 4.9 3.1�T (s) 290.7 249.5 420.3 316.7 271.7 240.0�T/ �N (s) 69.2 55.4 66.7 53.7 55.4 77.4

20 A. Campisano and C. Modica

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

the volume required for flushing operations. Values oft* 4 120 s lead to gradually decreasing percentages.

As an example, for typical values (Blokker 2006) ofVTC ¼ 6 l and QWB ¼ 0.08 l/s (t* ¼ 75 s), 74%(household 5) to 100% (household 6) of water neededfor toilet flushing can be provided by the reuse ofwashbasin grey waters.

As the characteristics of the reuse system are to betaken into account, water balance simulations on ashort time scale have to be performed on the basis ofacquired data. Results derived by these simulations arereported in the graphs of Figures 3 and 4 for the sixhouseholds. The two figures respectively report thecurves of WS and GWL as function of the dimension-less ratio R and for different values of t*. Reportedvalues of R and t* cover a large range of toilet cisternvolumes, grey water tank volumes and washbasin tapflow discharges (Blokker 2006).

Globally, despite of the heterogeneous characteris-tics of users in selected households, the graphs ofFigure 3 show quite comparable trends of the plottedcurves. This would encourage considering the possibilityto extend obtained results to other cases, notwithstand-ing the relatively small size of the considered sample.Increasing values of WS are obtained as t* decreases.According to the adopted reuse scheme, in fact, smallertoilet cisterns allow an increased number of flushingoperations with grey waters. Moreover the figure showsimproved performances of the system (increasing valuesof WS) as R increases (i.e. increased grey water tank

Figure 2. Values of VWB/VF as function of t* calculated onthe basis of �N and �T of the six monitored households.

Figure 3. Water saving WS as function of R and t* calculated on the basis of monitored data from the six households.

Urban Water Journal 21

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

volume compared to the toilet cistern volume). Inparticular, the trend of the curves points out that largerincremental benefits in WS are obtained for the lowvalues ofR (the curves show high slopes). Instead, watersaving becomes quite insensitive to increases in R forvalues higher than 10; in this case, values of WS areobserved to range between 35 and 100%depending on t*and (less) on the household characteristics.

Furthermore, the graphs show also that values of Rclose to 5 provide quite high water savings rangingbetween 32 and 96% depending on t* and on thehousehold characteristics as well.

As expected, the graphs of Figure 4 shows, instead,that water losses decrease as R is increased and thatvalues of GWL are significantly affected by variationsin t*. Also in this case, the curves present high slopesfor R 5 5 while grey water losses become quiteinsensitive to increases in R for R 4 10.

Globally values of R close to 5 were considered tobe suitable in order to reuse a large part of washbasingrey waters limiting the size of the grey water tank (andthe occupied space within the bathroom). For instance,

for the previously indicated typical values of VTC ¼ 6 land QWB ¼ 0.08 l/s (t* ¼ 75 s), a grey water tank of30 l (R ¼ 5) determines water saving ranging between50 and 77% with an average value (for the sixhouseholds) of about 62%. Correspondently, theaverage overflow losses result in between 11 and 46%with an average value of about 27%.

Considering that flushing volumes correspond toabout 30% of the total volume consumed in houses,previous results show that the investigated reusescheme (for R ¼ 5 and for all the considered t*) couldeasily allow water saving values between about 10 and29% of the total domestic consumption.

The detention times of grey water stored in the tankwere also investigated. In particular, values of thedetention time TD were calculated from collected datafor the different households as function of the greywater tank volumes and of the average daily grey watervolumes from the washbasin. In Figure 5 the dimen-sionless ratio TD

t� is plotted as function of R for theselected households. As expected, linear trends wereobtained for the curves showing increasing values of TD

t�

Figure 4. Water losses GWL (overflows) as function of R and t* calculated on the basis of monitored data from the sixhouseholds.

22 A. Campisano and C. Modica

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

as R increases. Considering values of R equal to 5 andt* ¼ 75 s (as in the previous example), relatively smalldetention times in the range 6.1 h (for household 3) to15.2 h (for household 2) can be obtained.

Concerning the economic feasibility of such a greywater reuse scheme, specific local conditions (localcosts, water availability, population habits, financialincentives, etc.) should be taken into account for theevaluations, considering also environmental and socialbenefits due to the water reuse.

Conclusions

The paper reports the results of an experimentalinvestigation on the evaluation of water saving fromthe reuse of washbasin grey water for toilet flushingoperation in domestic bathrooms. Six Italian house-holds characterised by a different number of userslargely heterogeneous in age, gender, occupation andcustoms were selected for the experiments and relativeuses at washbasin and toilet were monitored.

A preliminary evaluation of the acquired data atdaily time scale has shown the potential of reusing thewashbasin grey water for toilet flushing. For a moredetailed analysis that takes into account the technicalcharacteristics of the reuse scheme, water balances on ashort time scale were carried out. A simple systemcollecting washbasin water into a grey water tank andthen into the toilet cistern volume was considered forthe elaborations.

Specific variables were adopted to present theresults allowing to evaluate water saving benefits withdifferent values of toilet cistern volume, grey watertank volume and washbasin tap flow discharge in theranges of practical applications.

Globally, simulations have shown comparableresults for the six household. A grey water tank 5times greater than the toilet cistern results suitable toreuse large part of washbasin grey water (water saving

between 32 and 96%) to limit the size of the tank andthe grey water detention time. These results point outthat, with reference to literature total domesticconsumption, percentages between 9.6 and 28.8% ofwater used in houses could be easily saved by the reuseof washbasin grey waters.

References

Aylward, P.G., Casali, J.A., Porter, B.D., and Perjins, R.G.,2006. Grey water reclamation system and method forproviding and operating same. US Pat. No. 7,121,292.

Blokker, E.J.M., 2006. Modelling water demand patterns;description and evaluation of simulation model. SIM-DEUM, KIWA N.V., Nieuwegein. BTO 2006.010. InDutch.

Brennan, M.J. and Patterson, R.A., 2004. Economic analysisof grey water recycling. In: Proceedings of 1st Interna-tional Conference on Onsite Wastewater Treatment andRecycling, Perth, 11–13 February 2004, pp. 68–76.

Butler, D., Friedler, E., and Gatt, K., 1995. Characterisingthe quantity and quality of domestic wastewater inflows.Water Science and Technology, 31 (7), 13–24.

Campisano, A. and Modica, C., 2008. A system for thereclamation of grey waters from a source of grey waters,specifically from a wash basin, for rinsing a toilet and amethod for the operation of the system. EPC Pat. No.08160181.7-2303.

Christova-Boal, D., Eden, R.E., and McFarlane, S., 1996.An investigation into greywater reuse for urban residen-tial properties. Desalination, 106, 391–397.

Dixon, A., Butler, D., Fewkes, A., and Robinson, M., 1999.Measurement and modelling of quality changes in storeduntreated grey water. Urban Water, 1, 293–306.

Eriksson, E.H., 2002. Potential and problems related to reuseof water in households. PhD. Thesis, Environmental &Resources DTU, Technical University of Denmark.

Failla, B. and Stante, L., 2004. Aquasave Project. Experi-mental System for water saving in households, ENEAReport, EU Life Environmental Program, Bologna.

Friedler, E., 2004. Quality of individual domestic greywaterstreams and its implication for on-site treatment andreuse possibilities. Environmental Technology, 25 (9),997–1008.

Jefferson, B., Laine, A., Parsons, S., Stephenson, T., andJudd, S., 1999. Technologies for domestic wastewaterrecycling. Urban Water, 1, 285–292.

Lazarova, V., Hills, S., and Birks, R., 2003. Using recycledwater for non-potable, urban uses: a review withparticular reference to toilet flushing. Water Scienceand Technology: Water Supply, 3 (4), 69–77.

Li, F., Wichmann, K., and Otterpohl, R., 2009. Review ofthe technological approaches for grey water treatmentand reuses. Science of the Total Environment, 407, 3439–3449.

Maeda, M., Nakada, K., Kawamoto, K., and Ikeda, M.,1996. Area-wide use of reclaimed water in Tokyo,Japan. Water Science and Technology, 33 (10–11), 51–57.

McDonald, J.R., Henry, M., and Steele, R.J., 1993. Greywater recycle system. US Pat. No. 5,243,719.

Mukhopadhyay, A., Akber, A., and Al-Awadi, E., 2001.Analysis of freshwater consumption patterns in theprivate residences of Kuwait. Urban Water, 3, 53–62.

Figure 5. Values of TD/t* as function R for the sixmonitored households.

Urban Water Journal 23

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14

Surendran, S. and Weatley, A.D., 1998. Grey-water reclama-tion for non potable re-use. J. CIWEM, 12.

USEPA. 2004. 2004 Guidelines for water reuse. EPA Reportno. 625-R-04-108, Washington, DC, May 2004.

Vickers, A., 2001. Handbook of Water Use and Conservation.Amherst, MA: WaterPlow Press.

Winward, G.P., Avery, L.M., Stephenson and Jefferson, B.,2008. Chlorine disinfection of grey water for reuse:Effect of organics and particles.Water Research, 42 (1–2),483–491.

24 A. Campisano and C. Modica

Dow

nloa

ded

by [

Am

eric

an U

nive

rsity

of

Bei

rut]

at 1

6:17

17

Sept

embe

r 20

14