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Low Water Use Sanitation:The Design, Development

and Appraisal of aLow Volume Flush Toilet

in Botswana and Lesotho

OverseaS Development AdministrationFunded Research Project, 1983 - 1989

FINAL PROJECT REPORT, JULY 1989.

Professor J.A. SwatfleldDept. of BuildingHeriot - Watt UniversityRiccartonEdinburgh EH14 4AS

Dr RH.M. WakeHnDr R.A. BocarroDept. of Mech. Eng.Brunei UniversityUxbrldge LJB8 3PH

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LIBRARY, INTERNATIONAL REFERENCECENTRE FOR COMMUNITY WATER SUP~LYAND SANTAT~ON(IRC)P0. Box 93i50, 2b09 AD The Hagu.Tel. (070) 814911 ext 141/142

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Low Water Use Sanitation:—The Design, Development and Appraisal

of A Low Volume Flush Toilet in Botswana and Lesotho

by

Dr. R.H.M. Wakelin and Dr. R.A. BocarroDepartment of Mechanical Engineering

Brunei tJniversity, Uxbridge tJB8 3PH

and

Professor J.A. SwaffieldHead of Department of Building

Heriot—Watt University, Edinburgh EH14 4AS

ABSTRACT

In 1983 an ODA—funded programme was iriitiated to consider thefeasibility of development of a low water use w.c. designsuitable for installatiori in developing countries, particularlyin low cost housing.

The preliminary progranune concentrated ori modelling the keyhydraulic parameters of trap seal depth, trap seal volume andpassage width that govern w.c. performance at reduced flushvolumes. From this research, a rimless w.c. was developed.

The secondary phase of modelling was concerned with designing thew.c. to be upgradable from pour to cistern flush operation. Asthe w.c. pan was rimless, a device which was termed a “diverterbar” was designed to allow this flexibility. The final design ofthe prototype w.c. and diverter bar required a flush volume ofonly 3—4 litres compared to 9—10 litres for a conventional w.c.to pass the same laboratory tests.

From August 1985 to August 1988, ODA-funded overseas site trialsof some 150 of the prototype w.c.’s were undertaken in Lesothoand Botswana. The reduction of flush volume to 4 litres wasshown to have no adverse effect on long drainage runs. InBotswana, it was shown that the houses fitted with the prototype4—litre w.c.’s used a mean of 19 litres per capita per day lessthan the houses fitted with lO—litre w.c.’s. Expressed inpercentage terms, the savings by reducing the fiush volume were23 per cent. The percentage of the total household water usedfor w.c. flushing was 21 per cent for the houses with 4—litrew.c.’s compared to 40 per cent for the houses fitted withlO—litre w.c.’s. Similar savings were achieved in Lesotho, wheretrials concentrated on a range of sewage disposal methods.Additional benefits of low volume flush w.c. adoption wereidentified for on-site sewage disposal and storage, inciudingreduced conservancy tank emptying requirement.

As a result of the programme, further site monitoring inBotswana, site trials in Brazil, in conjunction with IPT SaoPaulo, and China, in conjunction with the Building ResearchIristitutes in Shanghai and Chengdu, are underway.

Contents Page

Introduction

Laboratory Development of the Low Volume Flush Toilet 2

Site Trials — Botswana 4

Site Trials — Lesotho 6

Conciusions g

References 10

Acknowledgeinents 10

Table 1 Water meter reading data analysed for 7

prototype group in Maseru

Low volume flush w.c. as installed inGaborone ~1est, Botswana and Maseru,Lesotho. Note design of the diverter barand the resulting water distributionaround the bowl ensuring surf acecleansing and efficient discharge.

Plate 2 View of the prototype housing group inGaborone West, Botswana. The 63 houseprototype group was located adjacent tothe smaller, 30 house, controlgroup.

View of a typical single storey lowincome housing scheme dwelling inGaborone West. Accommodation comprisedliving room, 2 bedroom , shower room andkitchen. Water and drainage wereprovided but no electricity supply.

Figure 1 Design criteria governing lowvolume W.C. performance

Figure 2 A comparison between the multiple baliefficiencies obtained by the Mark 0, MarkIII and ‘Field’ Mark III W.C.’s.

Figure 3 A comparison between the concentrationtest resuits of the Mark 0, Mark III and‘Field’ Mark III W.C.’s.

Figure 4 Bowi performance in terms of both solidand fluid contamination removal

Figure 5 A comparison between the prototype W.C.and B.S. clesigns.

Plate 1

- Plate 3

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flush

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Contents Page

Figure 6 A comparison between the transport testresuits of the Mark 0 and Mark III W.C.(with the Mark VI diverter bar).

Figure 7 The Mark VI P.V.C, diverter bar.

Site schematic drawing of the 63 lowincome B.H.C. house plots in GaboroneWest fitted with the 4 litre flushprototype W.C., and also showing themanhole locations and main drainageruns.

Water consumption and % saving data fromthe prototype and control group housingin Gaborone West, Botswana. Note thecomparabiiity of the sampie groups priorto the trial W.C. instaliation and theseasonal nature of the resuits.

Figure 10 Potential effect of changing the fiushvolume of the prototype W.C.

Figure 8

Figure 9

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INTRODUCTION

Water conservation policies are generaliy only initiated in timesof drought or disaster. Potable water, however, is a vitalresource and should be managed and planned accordingly. Theflushing of w.c.’s with typically 10—12 litres of water per flushis wasteful of this vaiuable resource and offers the greatestpotential for long term water conservation. Reduced w.c. flushvolume is applicable to developed and deveioping countries alikeand must be adequately researched to ensure maintenance of heaithand sanitation standards. The application of a sanitation systemsuch as the Ventilat:ed Improved Double Pit (VIDP) latrine may besuitable for rural areas, with a relatively low populationdensity, but is generally not suitable for the ever, and rapidly,increasing urban and suburban areas, where sewer connection ismore appropriate.

Valuable experience and insights into the hydraulic parametersgoverning low water use w.c. designs were obtained by the authorsduring a research project from 1978 to 1981, which successfullydeveloped a 4.5—6 litre flush volume close coupled w.c. for theUK market, funded by the UK Confederation of British CeramicSariitaryware Manufacturers (Uujamhan, 1981). In 1983 a f ive yearresearch project funded by the Overseas DevelopmentAdministration was initiated at Brunei tiniversity, and from 1985in conjunction with Heriot—Watt University, to design, developand site appraise a low volume flush w.c., with the co—operationof Twyfords Ltd. (Bocarro 1988). The project was also seen asrelevant to the United Nations’ International Decade of WaterSupply and Sanitation 1981—1990 and close liaison was maintainedwith other active groups, such as the World Bank’s TechnologyAdvisory Group.

Previous experience and discussions with the project sponsor,ODA, followed by a study tour of Africa, established variouscriteria for the project:

Ci) a flush volume of 3—4.5 litres would be realistic;

(ii) a washdown pedestal P-trap w.c. pan flushed by anindependent: cistern fitted with a drop valve would offerthe widest application. The potential to use locallyavailable cisterns and components was essential toensure availability of spare parts in the future;

(iii) the potential to offer a bucket/pour fiush w.c. pan,upgradable to cistern flush, should be considered. Theomission of a flushing rim, which could not be cleanedby pour flushing, would then be necessary and analternative method of flush water distributiondeveloped;

(iv) the necessity for simplicity of design and operation toensure adequate maintenance of the w.c. This ruled outsystems such as vacuum or pressure assisted solidetransportat.ion and the use of siphon break valves anddiaphragms;

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Cv) the predominance of single storey housing and buildingsin developing cour’tries minimises pressure fluctuationsin the drainage system and would allow reduced trap sealdepth, subject to sufficient depth to accommodateevaporative loss;

(vi) Gaborone in Botswana and Maseru in Lesotho would offergood potent:ial for site evaluation of the Low VolumeFlush Toilet (LVFT) under a wide range of siteconditions..

This report therefore presents the research and developmentnecessary to produce an appliance within these guideiines,together with an overview of the site evaluations in Botswana andLesotho.

LABORATORY DEVELOPMENT OF THE LVFT

A P—trap w.c. corLfiguration was adopted to conform to commonpractice in developi.ng countries. The modelling of the LVFT wasbased on a Twyfords B.S. 1213 P—trap w.c. from which both theflushing rim and trap seal back plate had been removed.Plasticine was used to remodel the internal shape of the bowl andtrap, and perspex back plates were fitted to vary trap sealdepth. A mechanical tipping bucket was developed to providerepeatable and representative pour flushing by bucket. Inaddition to British Standard 5503 tests, which inciuded the BaliTest, Paper Test and Sawdust Test, a range of discriminatorytests were used and developed to appraise w.c. performance.These tests inciudedt:

Ci) Multiple Bali Test using fifty 2Omm diameter balls ofthe same specific gravity which could b~ selected in therange 0.85-1.15. Discharge efficiency was calculated asthe percentage of bails discharging successfuliy.

(ii) Liquid Cont:amination Test using potassium permanganateto simulate liquid contamination of the w.c. trap.Light absorption, measured by a colorimeter, of a sampleof trap water taken after flushing compared to a sampletaken before flushing, caiculated as a percentagerelative residual concentration, gives an importantmeasure of flushing performance.

(iii) Modified Pa.per Test using 6 pieces of 125 x 125mmnewspaper.

(iv) Simulated Faeces Test using three 3Ommdiameter by lOOmmlong foamed plastic stools havirig a saturated specificgravity of 0.98.

Cv) Modified Bali Test using the B.S. 5503 bali, butrecording the amount of water discharged ahead of thebali relative to the flush voiume. This modificationproduced a useful degree of discrimination.

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(vi) Various bowi washing tests, inciuding the American ANSIAii2.19.2M (1982) test, which involves drawing ahorizontal line round the bowi 25mm below the rim with awater soluble ink pen and measuring the total length ofunwashed line after flushing.

(vii) Biotting Paper Test to measure spiashing from the bowlduring a flush by piacing a sheet of blotting paper overthe w.c. bowl and either estimating the area of wettedpaper or weighing the paper before and after flushing.

(viii) Transport Test using a 14 metre length llOmm UPVCdischarge pipe at a gradient of 1/80, connected to thew.c. Transportation performance of a model solid,typically a, half length C2 type maternity pad, wasmonitored by recording its velocity prof iie along thepipe and fitting a deceleration characteristic equation.Further details of this test method and the test rig areincluded in Howarth et al, 1980. This test provides thebasis for the definition of the required flush volumereiative to length and gradient of drain prior toconnection of discharge from other sanitary appliances.

Initiai development of w.c. trap and bowl shape were undertakenin the pour flush mode, and then later refined with cisternflush. With the omission of the flushing rim, it was necessaryto deveiop an alternative, but equaily effective, means ofdistributing the flush water around the bowi. A device termed a“diverter bar” was deveioped to fit onto the end of the fiushpipe. The diverter bar has two slightly downward angled sideslots with the primary function of distributing cleansing waterround the bowl and a bottom jet with the primary function ofinducing momentum transfer to solids in the trap. The diverterbar is connected to the end of the flush pipe with a sleeve toallow for different sizes of flush pipe.

The design criteria governing low volume fiush w.c. performanceare shown in Figure 1. Uujamhan’s work had identified a non—dimensional group determining w.c. performance (n), which shouldbe as low as possible, involving the parameters:

trap seal volume (S)fiush volume (F)trap seal depth (h)

and minimum trap passage clearance (w)as

n = ~ (1)

Extensive laboratory testing and development of trap dimensions,bowl shape, flush volume and fiushirig mechanism led to a finalw.c. prototype termed the Mark III w.c. and a Mark VI diverterbar which provided the optimum performance. This combination wasfinally appraised with a plastic cistern produced in South Africaand a modified ceramic Vaal cistern also produced in SouthAfrica. The ceramic cistern was adopted for the site trials inBotswana and Lesotho due to the fire risk caused by candlesplaced on a plastic cistern and also as no indigenous manufacture

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exists in Botswana and Lesotho of sanitary fittings. The plasticand cerarnic cistern fitted to the final version of the w.c. bowlwere terined the Mark 111 and ‘field’ Mark III w.c. respectively.As a comparison, the original Twyfords B.S. 1213 w.c., termed theMark 0 w.c., was also tested. Typical test results for flushvolumes between 3 and 9 litres are shown in Figures 2 and 3.

Figure 2 shows the results of the 0.85 specific gravity multiplebali test. The plastic and ceramic “cisterned” (‘field’) MarkIII w.c.’s performed similarly, and even at 3 litres performedbetter than the oric~inai (Mark 0) Twyfords w.c. flushing with 9litres. Similar conciusions can be drawn from Figure 3 whichpresents the resuits of the liquid contamination test, with alower residual concentration for the Mark III w.c.’s at 3 iitresthan the Mark 0 w.c. at 9 litres. The Mark III w.c.’s onlyrequired 2 litres to pass the B.S. 5503 paper and bali tests, butrequired 3.5 litres to pass the B.S. 5503 sawdust test.

The resuits confirmed Uujamhan’s functional relationship,equation (1) above, as represented in Figure 4, for both solidand fluid contaminat:ion removal. It is evident from Figure 4that the value of the dimensionless parameter plotted as theabscissa should be as iow as possible, subject to certainphysicai limitations. At an early stage in the development ofthe w.c., it was decided to adopt a minimum trap passage width(w) of 63min in order to meet dietary constraints. Considerationof drain pressure f].uctuation and trap seal evaporative iosssuggested that trap seal depth (h) could be safely reduced from5Ommto 36mm. These two limitations effectively dictated aminimum trap volume (S) of approximately 0.86 litres. Thedimensions of the Mark III w.c., the original Mark 0, B.S. 1213Twyfords w.c. and t.he requirements of B.S. 5503 are presented in

Figure 5. The value of the dimensionless parameter ~ for the

Mark 0 w.c. with 9.1 iitre fiush is 0.143. Substituting thelimits suggested above would require a flush volume (F) of 3.4litres to attain similar w.c. performance.

Resuits, in the form of solid deceleration characteristics, fromthe goud transportation tests are shown in Figure 6. Theseresults are presented as solid velocity along the drain, set at agradient G (defined as vertical drop divided by horizontaldistance), at distance L from the w.c. drain connection, plottedas ..jï77~ which has been shown to provide a iinear characteristic,Swaffield and Wakelin, 1976. From Figure 6 It is evident that aflush volume of 3 litres should only be adopted for drain lengthsof up to l1.2~ metres at a gradient ofl/80 prior to inflowconnection from other sanitary appliances. Most on—site sewagedisposal or storage systems would meet this restriction. Formain sewer connected drains a minimum flush volume of 4 litres isrequired to achieve similar solid transportation performance tothe Mark 0 w.c. flushed with 9 litres. These flush volumes weretherefore adopted for the various site trial coriditions.

SITE TRIALS - BOTSWANA

After compietion of the design and development phase of theproject, Caradon Twyfords of Stoke on Trent in the UK produced

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220 of the Mark III w.c. pans, the principal dimensions of whichare shown in Figure 5. An identical number of the Mark VIdiverter bars, the principal dimensions of which are shown inFigure 7, were machined from PVC by a local firm in Uxbridge.The overseas appraisal phase of the project, which commenced inAugust 1985, invoived ceramic cisterns. These site trials wereconcentrated in the capitals of Botswana and Lesotho.

The Botswana programme of prototype w.c. installations wascompieted by May 1986. The main concentration of installationswas in Gaborone where some 95 of the units are instalied. Theremaining 8 w.c.’s were instalied in Gumare.

There were several aspects of the monitoring. First of all,there were monthly inspections of all the project installationsin Gaborone. These inspections were used to identify anyproblems with the w.c.’s and to ensure they were functioningcorrectiy. The inspections helped to solve a problem with thecistern design. Once cured, none of the w.c.’s were leakingwater. Also, as a result of this monitoring, early instailationfaults were cured and eventually the frequency of maintenance waspracticaily negligible.

Three drainage surveys were carried out on an estate of 63 housesfitted with the experimental w.c.’s in Gaborone West. Figure 8shows a schematic layout of the house plots and the main drainageruns. The surveys were necessary to monitor tIie effect ofreduced flush voiumes on long drainage runs. The conciusion ofthe surveys was that the w.c. flush volume of 4 litres had had noadverse effect on arty of the main sewer lines or the house tomain sewer connections.

A detailed study was carried out on the same estate to determinethe effect of reduced fiush volume on household waterconsumption. Water readings were taken at 14 day intervais fromDecember 1986 to September 1987 and thereafter at 1 monthintervals to July 1989. A control sample of 30 houses with10—iitre w.c.’s, but. otherwise identical, was selected on anadjacent estate on the other side of the road and immediatelysouth east. The prototype group were found to use a mean of 2.4kilolitres less per house per month than the control group. Interms of litres per capita per day, water consumption in theprototype group of 69 lcpd compared to 88 lcpd for the controlsample, a difference of 19 lcpd. In terms of percentage savings,the prototype houses used 16—30% less water than the controlgroup. Household water consumption, and % water saving withrespect to the control group, over the monitoring periodDecember 1986 to July 1989 for the prototypeand control groupsare shown in Figure 9, and show consistent seasonal correlationof water savings. Figure 9 also illustrates that the waterconsumption for the prototype and control group housing prior tothe installation of the trial w.c.’s in the prototype group wassensibly identical over 12 months from February 1985.

Additional water dat.a were collected to determine the percentageof household water that was used for w.c. flushing. A prototypesample of 30 houses fitted with 4—litre w.c.’s and a controlsample of 15 houses fitted with lO—litre w.c.’s were used for the

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analysis. The resuits showed that the prototype group used 21%of household water for w.c. flushing and the control ~ample used40%.

This result was used to predict the savings that were possibleusing a range of flush voiumes from 2—13 litres, as shown inFigure 10. From a knowledge of the total water use during anyperiod in both prototype and control group dwellings, and theappropriate percentage used for w.c. flushing, the non—w.c. usagemay be determined. The number of w.c. operations for theprototype w.c. is also known from its flush volume, thus thehypothetical w.c. water use with any flush volume may be added tothe non—w.c. volume used. Thus a comparison between the controlgroup and the protot:ype group set to any flush volume may becarried out.

A study of the number of w.c. operations inherent in the controland prototype groups via fiush volume setting and w.c. totalusage illustrates that the prototype w.c. was normally onlyflushed once per usage, indicating the efficiency of the design.

This analysis technique could be used for future designcalculations and showed that the non—w.c. water use for both thecontrol sample and prototype sample were virtually the same.This result further justified the comparison between the twosamples taken of Bot:swana Housing Corporation low income housing.

A detailed questionrLaire was carried out on the same prototypeand control samples, priiuarily to assess user reaction to the 10wvolume flush toilets. From an analysis of basic data from thecontrol and prototype samples, it was apparent that the groupswere virtually identical in terms of population structure, age,employment, income and education. This result was a furtherjustification of selecting the two samples for comparison in thewater data analysis. The overall reaction to the prototypew.c.’s was positive.

All of the prototype w.c.’s installed in Gaborone werefunctioning at the end of the monitoring phase reported here inJuly 1989. However there were some major probiems encountered inthe one project site outside Gaborone. At a village school inGurnare, Northern Bot:swana, over half of the eight prototype w.c.installations were reported inoperable in November 1987. Faiiurewas due to brokert cistern components, lack of maintenance andintermittent water supply. It is apparent that much more robustcistern components and a user education programme are essentialfor adoption of water seal toilets in rural schools andinstitutions.

SITE TRIALS - LESOTHO

The site trials of the prototype w.c.’s in Lesotho had similarobjectives. The mortitoring of 53 w.c.’s inciuded further waterdata collection and guestionnaires to establish whether there hadbeen any adverse user reaction.

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In Maseru, Lesotho, fifty prototype w.c.’s were fitted in avariety of installations. Due to the differing town planningorganisation in Gaborone and Maseru It was not possible to locateblocks of dwellings for w.c. installation. Similarly a widerange of disposal methods, from septic tanks, to conservancytanks, main drainage and converted pit latrines were used. Thismade a systematic monitoring study, such as that possibie inGaborone West, impossible.

However, two types of monitoring was undertaken:—

1) Water readings t.aken from the records of the local waterutility in Maseru;

2) Frequency of conservancy tank emptying, again taken from thewater utility records.

An added complicat:ion in Maseru was that the low flush volumew.c.’s were installed over a period from October 1985 to August1986, thus no dear start date could be identified as inGaborone. Due to this It was necessary to compare the water usebefore and after installation in both the prototype and controlgroups to allow for the natural escalation of water use by thepopulation over this time period.

Table 1 iilustrates water meter readings for a small prototypegroup of 9 w.c.’s. The water data were collected from January1985 before installa.tion up to March 1987. The correction shownfor the control group water use rise varies with the installationdate and is based on a set of control group water data over aperiod from January 1985 to March 1987.

The overall water saving is shown as 37%, however the size of thesample is too small to make this a definitive figure.

House Mean Mean Month Increase Adj. %—AgeWater Water & year in water value change

Consuinp. Consump. of consump. for inbefore after instali. in control x, (x2—x1)/x1install. inst.all. group = x27x3of LVFT of LVFT

xl x2 x3 x2

21.87 23.83 9/85 1.42 16.78 23.27B 6.44 6.46 1/86 1.60 4.04 59.40C 9.46 9.28 1/86 1.60 5.80 38.69D 14.08 15.33 1/86 1.60 9.58 31.96E 5.36 7.74 3/86 1.49 5.19 3.17F 15.86 12.21 3/86 1.49 8.19 48.36G 52.77 42.46 6/86 1.41 30.11 42.94H 22.03 22.15 6/86 1.41 15.71 28.691 8.31 4.57 7/86 1.38 3.31 60.17

MEANx = 37.41

Table 1 Water meter reading data analysed for prototype group inMaseru

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The increase in control group water usage ratio followingprototype w.c. installation varied with installation date. Theratios presented in Table 1 were calculated as foliows:—

Let c1 be the control group water usage per month from January1985, i = 1, to March 1987, 1 = 27. The monthly figures wereagain corrected from the rather variable meter reading dates toyield comparable monthiy averaged figures.

Assume that the particular prototype w.c. was instailed in March1986, thus 1 = 15.

The control volume data was manipulated as follows to give theincrease ratio, r.

r = Mean cj(i = 15 to 1 = 27) water consuxnptionMean C1 ci = 1 to 1 = 14) water consumption

Siiuilarly the water utility conservancy tank emptying data wereused to ascertain whether savings were being made by low flushvolume w.c. users. Ten installations were used for the prototypegroup, five existing tanks as a control group. The frequency ofemptying was monit.ored from April 1985 — October 1986. Anidentical technique to that shown in Table 1 was used todetermine the reduction in tank emptying, corrected for thenatural escalation in water use in Maseru.

The result of this monitoring was an overall reduction of 0.45tank emptying visits per month per prototype dweiling, or roughlya 1/3 reduction over the year in total visits. This figure isbroadly in line with the water meter readings for the sewereddwellings in Tabie 1. In Maseru all installed w.c.’s werenormally set to 3 litres flush volume, so the greater savingcompared to Gaborone was to be expected, however tank emptying isa non exact measure and again the number of dwellings involvedwas small and, due to the local conditions in Maseru, all thedwellings of both prototype and control group were significantlydifferent to each other.

At the end of the monitoring period, all but two of the w.c.’swere in use. One w.c. was not in use as the cistern inlet—valvehad been damaged. In the other case, the w.c. had been connectedto a waste pipe which habitually blocked. Investigationattributed the cause to a poorly levelled pipe, which was to becorrected.

The deveiopment and instailation of a two compartment septic tankand shallow soakage pit accepting discharge only from the 3 litreflush toilet proved successful on six sites. Another successfuidevelopment involved the upgrading of a VIDP lat.rine to a twocompartment septic tank and soakaway accepting discharge from the3 litre flush toilet installed in the house. The latrine slaband superstructure were retained in case of future drought.Further monitoring will be required of these developments toestablish their long term potential.

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A user questionnaire was again used to establish whether therehad been any adverse user reaction to the w.c.’s. The majorityquestioned preferred their new w.c. but the main criticism wasthat the w.c. was prone to fouling by excreta near the watersurface.

In Lesotho, It was shown that the prototype w.c. would also workin its pour—flush mode. For the particuiar installation only 2iitres were required per flush. The lack of potential pour flushclients proved that people’s aspirations are for water mainsconnected cistern fiush toilets and pour flush does not meetthose aspirations in Lesotho.

CONCLUSIONS

1. From a study tour in 1983, at the start of a 5 year ODA—funded research project, the need for water conserving w.c.designs was established and Lesotho and Botswana wereidentified as suitable locations for site trials.

2. Development of a. rimless washdown w.c. pan was carried out inconjunction with Twyfords, who produced prototypes and 220 ofthe final design for the site trials.

3. A device known as a diverter bar was designed to allow thew.c. to be upgraded from pour—flush to cistern—flushoperation.

4. An experimental programme showed that the prototype w.c.required a minimum of 3 litres to discharge faeces and urine.However, a minimum of 4 litres was required for satisfactorytransport performance.

5. Overseas site trials of some 150 of the prototype w.c.’s werethen undertaken in Lesotho and Botswana. This study was aunique evaluation of the transport performance and watersaving potential of low volume flush toiiets.

6. The programine in Botswana proved that the reduction in fiushvolume had no adverse effect on long drainage runs.Furthermore, the installation of the prototype w.c.’s had ledto substantial water savings of 16—30%. A survey also provedthe user acceptability of the design.

7. The programme in Lesotho endorsed all the resuits of theBotswana study. It was also shown that only 3 litres perflush were sufficient, if sewage disposal was on-site ineither a septic tank or conservancy tank with up to 10 metresof interconnecting drain.

8. A cost benefit analysis showed that water conserving designscould be cost effective, especially if water tariffs are setto encourage water conservation.

9. The design and development phase of the project are nowcomplete. The prototype w.c. has been proven to worksuccessfully and it would appear to be cost effective todevelop w.c.’s that require 4 litres or less. It is hoped

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that this research will encourage w.c. manufacturers toproduce such designs. Indeed, a firm in Zimbz~bwe are nowproducing a fibreglass design, based on the 3—4 litre flushprototype w.c.

10. The project has been extended with ODA and British Councilsupport in Brazil, where IPT in Sao Paulo has participated inthe setting up of further site trials, invoiving theinstallation of 30 LVFT at San Carlos. IPT will be involvedin monitoring water use and undertaking user surveys.

11. Six LVFT have also been supplied to the People’s Republic ofChina and init:ial site evaluations will take place inShanghai and in Chengdu. Under ODA funding initial visits tothe Shanghai Research Institute for Building Sciences and theSichuan Institute for Buiiding Research have been undertakenand detailed discussions held with ceramic manufacturers inChina. This extension will hopefully iead to a fullmanufacturing programme.

REFERENCES

Swaffield, J.A. and

Wakelin, R.H.M.

Howarth, G.,Swaffield, J.A. andWakelin, R.H.M.

Uujamhan, E.J.S.

Bocarro, R.A.

ACKNOWLEDGEMENTS

“Observations and analysis of parametersaffecting water solid transport ininternal drainage systems”The Public Health Engineer, Vol. 4, No.6, November 1976.

“Development of a flushability criterionfor sanitary products”CIB/W62 meeting, Brunel University, 1980.

“Water conservation w.c. design: a studyof the design parameters affecting w.c.performance”Ph.D. Thesis, Brunei tJniversity, 1981.

“Water conserving w.c. designdeveloping countries”Ph.D. Thesis, Brunel University, 1988.

for

The research reported was supported by an Overseas DevelopmentAdministration awardL initiaily to Brunei University and lateralso jointly to Heriot—Watt University. This support isgratefully acknowledged.

Caradon Twyfords provided manufacturing support and producedLVFT installed in Botswana, Lesotho, Brazil and China.

the

The overseas site trials would not have been possible without theactive support of the Botswana Housing Corporation and theBotswana Ministry of Local Government and Lands and, in Lesotho,the participation of the Urban Sanitation Improvement Team inMaseru. The contribution of all members of - these organisationswho participated in the reported research is gratefullyacknowledged.

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Fiush volume, Fdependent onflushing mode,sewage disposaltechnique,drain iengthand gradient

Trap sealdepth, h, dependantupon pressurefluctuatlons indrainage systemand trap evaporatlonrate

Cholce of cistern orpour flush operatlon

Water distributlonaround bowi, cholceof cistern withsiphon or drop vaive

Minimum trappassage clearance,w, possibiy dietdependant

Water surface area limit setby need to avold surface fouiing

Figure 1Design Criteria Governing Low Flush Volume W.C. Performance.

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Plate 1Low volume tlush W.C. as Instaiied InGaborone West, Botswana and Maseru, Lesotho.Note design of the diverter bar and the resuitingwater distribution around the bowi ensuringsurface cleaning and efficlent discharge.

1

—~--~

/

nA

-r

S

04-

4-

0

00

0)4-

(50

t t t

Specific Gravity of Bails = 0.85

2 Mark III W.C.

1 ‘field’ Mark iii W.C.

t 1 t

Flush Volume ( litres)

50

i:o 2**’~~hh1~

80 -

-~ 70-¼~~

>1

60-0

50-

40 -

0 0 Mark 0 W.C.

300 1 2 3 4 5 6 7 8 9

Figure 2A Comparison Between the MultipleBali Efficlencies Obtained by theMark 0, Mark III and‘Field’ Mark III W.C.’s.

40

30

20

10

Figure3

A Comparison Between the 0Concentration Test Results of the 2 3 4 5 6 7 8 9

Mark 0, Mark Iii and‘Field’ Mark lii W.C.’s. Flush Volume ( Iltres)

13

50 //

/

Trap Vol.Flush Vol.

Trap seal depthPassage width

Figure 4BowI Performance In Terms of Both Solid and Fluid Contamination Removal.

100%

Bowi efficlency defined as:-

n5 = No. 2Omm balls, constant s.g. discharged

Reslduai conc. Potassium permanganateinitiai preflush trap conc.

1.4%

Gooddesign (n5 )

Gooddeslgn(n~ )

0 .2 .4 .6

14

L

c

D.scription BS 5503:pt 2 TwyfordaBS1213p - trap W.C.panMark 0

Mark IiiW.C.

Depth of watersaaiii

50 min 56 36

Clearancsbelowtip of plat.R

75 mln 77 69

Trapsaaivolume n /a 1.79 L 0.86 L.

Watersurtace:

backtofrontE

sldetosldeG

lSOmln

ilOmin

165

113

406

118

79

390HelghtA 390+10

Distancefromtip of backplat.to lnsidefaceoffiush rim B

70 max 30

260

32

275Wldth ofopening M

240 min

Length ofopening L.

290 min 320 320

WldthofpanN

360+10 355 350

Heighttocentre ofW C. outtet K

190 191 190

Figure 5A Comparison Between the Prototype W.C.

15

z

and BS. Deslgns.

(1)

000>

1.2

1.0

0.8

0.6

0.4

0.2

0 10 20 30 40 50 60

( L / G )112 ( m112

Figure 6A Corn parison Between the Transport Test Resuits of theMark 0 and Mark iii W.C. (WIth the Mark VI Dlverter Bar).

16

25

1 .8mm slit saw cutwlth a 1 .8mm PVC platecut to size

All dimensions in mlllimetres

Flgure 7The Mark VI P.V.C. Diverter Bar.

1100

26

17

Plate 2View of the prototype housing group InGaborone West, Botswana. The 63 houseprototype group was located adjacent to thesmaller, 30 house, control group.

1~

13/:;

rIJ~-

Ii

1

cri~a

Figure 8Site SchemaLtic Drawing of the 63 Low Income B.H.C. House Plots InGaborone West Fitted With the 4 Lltre F!ush Prototype W.C., and alsoShowing the Manhole Locations and Main Drainage Runs.

19

Plate 3View of a typical single storey 10w Incomehousing scheme dwelllng In Gaborone West.Accommodation comprised llving room,2 bedrooms, shower room and kltchen.Water and drainage were provided but noelectrlcity supply.

r

iiiS~

T

1

- ~- ¶

11

t ¶

L 1 tre3/hou3e/dey.

300 400 500 600 700 800

50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 600 850900

Figure 9Water Consumption and % Saving Data from the Protoype and ControlGroup Housing in Gaborone West, Botswana. Note the Comparabliltyof the Sample Groups Prior to the Trial W.C. Installation and the SeasonalNature of the Results.

In~tal1atIonPer lod.

*+

1

Control groupPre—prototype group

* Control group+ Prototype group

—500 —400—300—200 —100 0 100 200

Dey count From 3t t t t

Dec. 1986.

- Z Water sev t ng wrt Control group.

1 t t 1 1 t t t t t 1 t t t t t 1

3~.

3C —

2(

1 t ~t I~ 1~i - t - ~ey coun~From 3 Dec. ~

21

£

>(5

(1)

04-(5

FIgure 10Potential Effect of Changing the Flush Volume of the Prototype W.C.

t 1 t 1 t 1 1 t40

30-

20

10

0

-10-

-202 3

L~ ~

4 5 6 7 8 9 10 11 12 13

Flush Volume of Prototype W.C. (litres)

22

-c.4 ¶t

t.Pl t - _*1 0

t