A Methodology For Surveying Domestic Water Consumption

 

A

Methodology for Surveying Domestic Water Consumption

B y K. EDWARDS, BSc, CEng, MICE Member) a n d L. MARTIN, MA, F G S Member)*

ABSTRACT This paper describes the experimental design and engineering of the largest contemporary survey are of domestic water consumption in the UK. Results presented for the first first full year of data co llection and are discussed in term s of ex planatory variables, reliability and usefulness. Sign ificant findings include (a) the range o f p e r capita consumption, (b) relationships to explanatory variables, variables, (c) (c) componen ts of consumption includin g llegitimate egitimate night flows, and (d) the contributiyns of specific domestic appliances. demand; domestic use; use; leakage; Key words: Consumption; demand; metering; night flows; tariffs; water consumption.

INTRODUCTION

programme was that of the National Metering Trials(’)which Trials(’) which took place between between 1989 and 1993 in twelve locations, mostly in southern and central England. Other long-term studies had been undertaken by South West Water(*) nd S evern Trent Wated3).HowWated3).However, none of these was able to provide Anglian Anglian Water with the specific information required because, although these studies may have been representative of their own area, they failed to provide data which could be reliably transferred to the region of East Ang lia. The Na tional Metering Trials were not establis lished hed to be studies of dom estic estic consumption per se, and the regional studies in South West and Severn Trent Water were only statistically relevant to their respective regions.

Since privatization, a key element of water com-

REGIONALPECIFICS

panies’ concerns has been the charging method which should be adopted for domestic customers. Options for charging depend upon a detailed knowledge of customer water use, accurate forecasting of future demands and the temporal and spatial variability, together with their causes, which underlie these patterns. Reviews of existing studies confirmed the opinion that the Ang lian region region was unique w ithin ithin the UK in terms of climatic and, above all, socio-economic parameters. No current analysis analysis provided the necessary data which the company required; therefore a five-year study was sanctioned to to examine both the compon ents and the variability variability o f domestic consumption within East Anglia. This paper examines the engineering behind this survey and presents results for

The East Anglian region is unique in the UK. Clima tically, it has the most continental climate climate of the U K its soils are mostly derived from from quaternar quaternaryy depo sits with with a high percentag e of glacial gravels and sands, and there is a n unusual mixture of heavy clays adjacent to very light sands/sandy loams. From a socio-eco nom ic perspective, the region is o ne of high growth potential (albeit latent in the 198Os/early 1990s) and ne t po pulation migrational influx. influx. A s such, East Anglia does not possess the same econogeog raphical structure as any other part of the UK. N o water consumption studies were available which could exp lain the likely pattern of d om estic water use in this part o f he coun try. It was therefore decided that the investm ent, which was required in establishing a full survey of domestic consumption in the East Ang lian region, would be justified. In 19 91, approval was given to the undertaking of the comprehensive survey of domestic water consumption, known as SODCON.

the first full twelve months of data. The survey is known by its acronym ‘SOD CON ’. BACKGROUND OTHER TUDIES

OBJECTrVES

In the late 1980s, many studies were addressing, both directly and indirectly, the issue of dom estic metering and domestic consumption. The most well-known

The m ain purpose o f he su rvey was to aid the selection of A nglian Water’s future charging method and ttoo enable the com pany to manage its water resources resources to to meet future demands. SODCON was therefore designe d ttoo pro vide the follow ing information: information:

This paper was presented for discussion at a meeting of the East Anglian Angl ian Branch, held on 11 Ma May y 1994.

(i) An explanation explan ation of the factors that determine unmeasured water demand; (ii) Details of the patterns of water consumption across across

*Customer *Custom er Services Support Manager (and SODCON Project Manager) and Huntingdon, Marketing Development Manager, respectively, Anglian Water, Cambridgeshire, UK. JCIWEM 1 9 9 5 ,9 , October

different household, economic types;

soil,

climatic

and

socio4

 

EDWARDS AND MARTIN O N (iii) Estimates of demand responses to different tariff structures, analysing the effects effe cts arising from from dif ferent charging options; (iv) Detailed costs of metering; (v) Aggregate estimates of per capita consumption for use in demand forecasting and investment appraisal; and (vi) Estimates of leakage, legitimate night night use and the development of an economic leakage control model.

As an experience added benefit, company obtain valuable in thethe in field of publicwould relations and gain a substantial database database of socio-economic information in respect of its domestic customers.

EXPERIMENTAL DESIGN SAMPLING

For the survey to be statistically robust it had to identify all the characteristics which which were likely to explain variations in consumption. A sample of approximately two thousand households was chosen for the 1 1 1 survey. They all had meters and data loggers installed externally, as detailed below. This is a relatively small sample in relation to the 1.4 million unmeasured households in in the region, and it was recognized that a random distribution would not give sufficient confidence. A structured, stratified stratified approach was was therefore selected. It was decided to sample households households in clusters, divided into divisional sub-samples according tcr tcr the balance of population in each, and stratified by ACORN A Classification Of Residential Neighbourhoods). ACORN is a geodemographic classification system for small aread4),which aread4),which classifies enumerate districts (EDs) according to simitarity across selected census variables. The sampled clusters were allocated to 50 public water supply zones picked as areas within which these households were were located. Each zone was checked to ensure that all climatic and soil types, typical of the region as a whole, were represented. This segmentation would allow for the significance of garden watering to be measured. A Simi Similar lar check was made to to locate sites with pipework of differing 5ges 5ges and buried in differing soil types. In the Anglian region it was determined that there were three climatic zones where rainfall tended to be heavy, medium or light. Similarly there were three soil types; heavy (clay), medium (chalk) or light (sandy). The age of the network was classified as ‘pre-war’, ‘1950s’, ‘1970s’ and ‘modern’. It was felt that there would be sufficient correlation between age and pipeline materials, therefore no fiuther subdivisions were made. The ACORN classifications which were used for the sample were consolidated into eight groups: u) Housing in agncultural areas; (b) Modem family housing, housing , higher income bracket; intermediate e status; c) Older housing of intermediat

478

d) Older terraced housing;

e), 0 g) Council housing (three categories); (71) High-status non-family areas; i) ffluent suburban housing; and 0) Better-off retirement areas.

SPECIFICTUDIES

Within the sample of 2000 households a sub-set of one hundred was selected special100’ investigation. These were known as the for ‘Golden and each each property therein had, in addition to its external meter, every separate water-using appliance monitored individually at its point of use. To further develop Anglian’s understanding of the effects of metering on demand, a further 1000 customers were recruited. These customers were already paying for their water on a measured basis, by by meter. They undertook the same socio-economic interviews, interviews, but their meters were read manually at a monthly monthly fiequency and their patterns of consumption were compared with the SODCON database.

PROJECT ENGINEERING TIMESCALE

The overall project has been planned to run for five years. The first year was used for setting set ting up and engineering the project, and the remaining four years are being used for collecting data and carrying out analysis. Table I lists important dates and actions.

TABLE I.

KEYDATESN SODCON PROGRAMME

Action Pilot 2000 volunteers

I

Dates

1855 meter units installed installed in highway 145 internal meters installed installed

Jul, Aug 199 1 Oct, Nov, Dec 1991; Jan Feb, Mar 1992 Nov, Dcc 1991; Jan, Feb, Mar 1992 Feb, Mar, Apl 1992

63 mains meters fortoleakagi Install meters andinstalled telemetry

May, Jun, Aug, JuI1992 May, Jun, Sept 1992

Socio-economic questionnaire completed Property and appliance survey completed Build input and output data programmes

May, Jun, Jul 1992

‘G100’

May, June, Jul, Aug, Sept 1992 Oct, Nov, Dec I99 1 Jan, Fcb, Mar, Apl, May, Jun, Jul, Aug, Sept 1992

MANPOWER

Seven full-time staff are employed on the project and two contractors are engaged to read meters and data loggers and change ‘meters when necessary. In addition, they also carry out any plumbing maintenance i-equiredin the so-called ‘Golden 100’ houses. houses. The staff comprise a market research coordinator, based at AWS regional headquarters, and four market research officers, one in in each Division. The latter are JCIWEM 1995,9, October

 

A METHODOLOGYFOR SURVEYING DOMESTIC WATER CONSUMPTION CONSUMPTION

responsible for most of the activities in their divisions and manage their stand-alone compu computer ter databases. A systems analyst programmer and a principal engineer specializing in telemetry systems are also members of the team. Economic consultants have have been engaged to advise on the project design and to analyse the data.

PILOT TUDY A pilot study was designed to gauge customer reaction to an in-depth study of domestic water consumption and two questionnaireswere used, one in the form of a diary of water use and the other for socioeconomic information. The pilot study was carried out in the Northampton area for a period of six weeks during the months of July and August 1991. Fifty households who were already paying their water charges on a metered basis took part in the study. The volunteers’ meters were read manually four times each day for the duration of the pilot, then the diary and socio-economic data were matched to the meter readings to establish if there was any correlation of water use. The following lessons were learned from the pilot study: There was sufficient evidence to justify carrying out the full survey; People generally were were interested in how water was used and were willing to join in the surv survey. ey. Of Of the people contacted to take part part in the pilot study, 50 agreed to participate; Volunteers were were not aware of the project in advance, and a substantial amount amount of time was spent explaining what the survey was all about; Customers were far more receptive to talking to staff in uniform and using a clearly marked Anglian Wate Waterr vehicle than to staff not in uniform and using unmarked private vehicles; Volunteers were reluctant to give details of their earnings because the questions were too specific; and Diary forms were not completed accurately because volunteer s had to fill in too much detail. detai l.

The following action was taken to address the problems which were identified in the pilot study: Information leaflets about the project were prepared and sent out with a mail shot in advance advan ce of calling on propective volunteers; A decision d ecision was made that the market research officers would wear a uniform and use clearly marked Anglian Water vehicles; The diary form was made more user-friendly, user-frie ndly, as a tick sheet, to improve accuracy; and The socio-economic questionnaire questionn airewas was altered to give wider earning bands.

M A I NODCON

STUDY

Meters and D ata Collecti Collection on It should be remembered remembered that the survey comprised volunteers who pay their water charges by rateable value but have agreed to have meters installed to their J.CIWEM, 1 9 9 5 ,9 , October

water services. The meters have been mainly sited in the highway at the boundary to the properties but, when shared Services were identified, some meters were installed at the point where the services split within the boundaries of the property - mostly in the gardens. However, 145 meters were installed inside properties because it was impossible to fit these satisfactorily outside. Pulsed meters which provided a pulse pulse for every litre of flow were chosen for the project. Three types of domestic meters were chosen: (i) Schlumberger P40s (installed outside properties); (ii) Kent pulsed output output meters (installed inside properties at the stop-tap position); and (iii) Andrae Leonberg Leonberg turbine turbine (used inside inside homes at every point of use).

The loggers which were used to collect collect the meterreading data from the Schlumberger and Kent meters were Newlog Universal loggers supplied by Technolog Ltd. These loggers record the flow of water (in litres)) every 15 mins and can litres ca n hold up to three months’ data. The loggers are down-loaded to disk using Toshiba computers by the meter readers, then the disks are sent to headquarters for processing. Datavalidation rules have been established to determine whether the retrieved data can be accepted automaticautomatically or if the reviewer has to examine it it first. For the ‘Golden 100’ properties, proper ties, a Kent pulsed pulsed output meter was installed insta lled at the internal stop-tap location as a reference meter, and Andrae Leonberg meters have been fixed in positions where they are at least obtrusive to each appliance. There are, on average, fourteen fourte en meters meter s in each household. It was important impo rtant that that the meters used in the ‘Golden 100’ households househol ds did not have registers registe rs that the volunteers could co uld read and, as a s a result, res ult, influence the way they would normally use water. All these meters are scanned by telemetry every 15 mins using Micro Medina outstations to hold the information, hen they are downloaded using PSTN lines to Anglian’s headquarterss during the night. All the same data-validation quarter rules apply a pply to these households house holds as to to the other 1900;in addition, the summation of all the small meters are checked against the reference meter on a daily basis.

Household Surveys Two types of survey have been carried out with all the volunteers; a property and appliance survey and a socio-economic survey. The property and appliance appliance survey was carried carri ed out by the market research officers listing and numbering number ing all rooms in the property and all water-using appliances in in each room. In addition, the the areas of garden which which could be cultivated (or were set to lawns) were measured, as this would have an influence on garden watering. A detailed socio-economic questionnaire was was compiled and carried out by the M O M organization. Questionss included: numbers and ages of people in the Question household, their qualifications and income, and mat479

 

EDWARDS AND MARTIN O N

ters of hygiene (for example, how many baths did people in the household tend tend to have each week). The response was excellent: excellent: 94 of the households responded to the interview interview without the the need for further requests. In addition to the surveys, all householders except the ‘Golden 100’ were asked to com plete a diary of their water use for one week. This w as required to to try and m atch the water use against the m eter recordi recordings. ngs.

mation to the databases without travelling to their offices. The market research officers have been trained to carry out socio-economic and social-class classification interviews, and it was essential that all interviewing was carried carried out in a professional manner. All All questionn aire forms are h and-de livered by the m arket research officers so that face-to-face face-to-face contact wit hth e volunteers is maintained. Payments are made each

Clipboards with with appropriate appropriate proformas proformas w ere given to the volunteers by the market research officers when they were carrying out the property and appliance survey for each room in the house w hich had water-using appliances. At the time the volunteers were asked to complete a w ater-use ater-use diary for one week starting starting the the following Monday. The market research officers explained the the reasons why the diaries were required and answered any queries which had been raised by the volunteers.

year to the volunteers in recognition of their cooperation and con tinued support.

Computer Systems The computer system has has been built in two parts: an input system is used at division level and the central output system is o perated at regional headq uarters. A personal computer (PC) based data system with office-based and portable PCs was set up at the start of the project to handle the market research officers’ records, and this this has been extended to allow network transfer transf er of the data to headq uarters. uarters. The input system was developed by a contract firm firm (Logica) and tested with live data in March 1992. Data collection from from meter loggers is taken by portable PCs, and the system has been developed to allow collected data to be uploaded onto the office-based office-based PCs and validated. validated. It also reviews and va lidates data collected by telem etry. The disk space required for SODCON is about 6. 5 gigabytes; approximately 3500 points are processed each day, wh ich amounts to 3500 megabytes of data. Customer Care It was recognized at an early stage that the whole project would depend on custom er care. Accordingly, Accordingly, it was decided that the m arket research officers wou ld become the v olunteers’ contact for any matter associated with Anglian Water, not just SODCON. They would become a name and, more importantly, a face to the volunteers. Each market research officer had a telephone and answering machine installed in their homes. At the o utset, when the mail shot and pamphlet (explaining the project) was sent out to the prospective volun teers, the m arket research officer’s business card (with their office and home numbers) was included, with the request that the volunteers contact them at any time at the office or at their home s. About 60 of the volunteers are only contactable out of normal working hours, therefore it is essential that market research officers work flexible hours. Each officer is provided with a laptop computer which allows them them to work from their homes and input inforinfor480

RESULTS At present, data from April 1992 to O ctober 199 3 are being used for analytical purposes. Although there will never be complete data for the whole sample of 2000 properties properties because of mechanical failures failures and som e attrition, attrition, the samp le is of sufficient sufficient size to to give complete confidence in the data accuracy and reliability. The results, covering the period to October 1993, represent the first fully validated set of data. As su ch, there are several areas of work, notably leakage, whe re analysis is (as yet) inco mp lete, but the m ain findings are given below. PATTERNS F USE capita ta SODC ON’s data data for the distribution distribution of pe r capi consumption (PCC) shows an average value of 145 lihead. d, but, as wou ld be ex pected, there is a considerable range (Fig. 1 ). Mo nthly variations in in total consumption are presented in Fig. 2, and the expected diurnal consum ption patterns have bee n recorded; an example of this is presented in Fig. 3 . Weekly flow patterns are show n in Fig. 4. A detailed analysis of flows has determined that legitimate night-time consumption (strictly speaking ‘householdnight ‘household night use’, provided that underground sup-

ply pipe losses and plumbing losses can be excluded) in the reg ion is ap proxim ately 2.5 Uproperty. Uproperty. h, and is normally codsistent throughout the week (Fig. 5). RELATIONSHIPS Analysis of S ODC ON data have provided interestinteresting data o n the following relationships relationships between PCC and a number of variables: a) Household size;

6) Housing type ACORN groups);

Socio-economicgroupings (income bands); and d) Rateable value value of proper ties;

(c)

and these relationships are presented in Figs. 6-9. F CONSUMPTION DETAILEDATTERNS DETAILEDATTERNS An analysis of the data provided by the ‘Golden and the 100’ volunteer households has comm enced, and

J CIW EM , 1 9 9 5 ,9 , October

 

A METHODOLO ME THODOLOGY GYFOR S SURVEYI URVEYING NG DOMESTI DOMESTIC C WATER WATER CONSUMPTION

Per capha consumption (1lhead.d)

Fig. 1.

per c apita consumption Distribution o f daily per

1504

140

1204

100

'I

, Oct

Fig. 2.

'

Nov

Dec

Jan

Feb

Mar

Month

Apr

May

Jun

Jul

Aug

Sep

Daily per capita con consum sum pti on Octob er 1992 1992 t o September September 1993) 1993)

J U W E M 1 9 9 5 ,9 , October

48

 

EDWARDS AND MARTIN ON 30

O

k

6

0

18

12

Time of day houn)

Fig. 3.

Diurnal pattern of water use

200

150

m

100

A

50

0

SUN

MON

TUE

WED

THU

FRI

SAT

Day of week

Fig. 4.

Mean dail y PCC

overall pattern of appliance a ppliance use is shown in Fig. 10.Many variations underlie this overall pattern, as can be seen by the comparison of two individual households (Fig. 11).

DISCUSSION QUALITYONTROL

One of the most critical aspects of all surveys of 482

domestic consumption is that of quality qu ality control. South South Westt Water have one of the country's Wes cou ntry's longest running continuous surveys of demand, and they have estimated(5) hat 15 of their data set significantly alters every year, in terms of household size, occupation bands, or socio-economic status. The need to ensure that data on the sample set are sufficien suff iciently tly up-to-date up-to-date is an ongoing ongo ing and paramount requirement, and there is a continuous recru recruitm itment ent drive for new volunteers. To date the current number of SODCON participants is 1929. JCIWEM 1 9 9 5 , 9 , October

 

A METHODOLOGY FOR SURVEYING DOMESTIC WATER CONSUMPTION 3

2.5

2

c

E

1.5

e

1

0.5

0

Sun

Mon

Tue

Wed

Fri

Thu

Sat

Day

Fig. 5.

Night-time consumption per property

Naturally there has been some attrition to the SODCON sample. Approximately 7 of the sample have already moved house and there have been births and deaths. In addition, a number of households have elected to pay their water charges by volume, but new households will continue to be included include d to maintain the sample of approximately 2000 households. Regular up-date questionnaires will be asked of the volunteers

to maintain accuracy of PCC and socio-economic trends. OF USE

The figures for per capita consumption show the expected wide range of values about the mean mean of 145 l/head.d. l/hea d.d. All All observation observ ationss have been included in the

250

200

150

C

100

50

0

I

1

2

3

Fig. 6. J.CIWEM, 1 9 9 5 , 9 , October

5 4 Number in household

6

7

8

Mean PCC by househol household d size 483

 

EDWARDS AND MARTIN ON 180 160 140 120

-

100

a l

3

80

60 40 20

0

A

C

E

D

F

J

K

ACORN

Fig. 7.

Mean Me an PCC by ACORN classification

160

155

150

1

145

140

135

130

High

LOW

Household income

Fig. 8.

Mean Me an PCC by household income

analysis, although some are clearly ‘outliers’. The average value for PCC PCC accords with the estimate for domestic consumption used by Anglian Water and aligns with other companies’ data but, for the reasons given earlier, it would be wrong to draw any close 484

I

comparisons with other studies. SODCONwas originally designed to meet meet Anglian’s needs alone, but it is reassuring that the data also appears appea rs to be representative of other areas. However However,, it must must be recognized that SODCON SODCON proJ.CIWEM, 1 9 9 5 ,9 , OLhber

 

A METHODOLOGY FOR SURVEYING DOMESTIC WATER CONSUMPTION

250-

200

Highest

Lowest

RV bands

Fig. 9.

Mean Mea n annua annuall household consumption b y RV band

vides actual consumption data, and these patterns are influenced by dynamic variables such as weather and the economy. No-one would expect the period October 1992 to September 1993 to be ‘typical’. The economic econom ic recession will have had an impact on domestic dome stic demand, both in terms of absolute levels of consumptionand the timing of water use. The summer of 1993 was spectacu-

larly wet and dull. Very little, l ittle, if any, garden watering was carried out during the first period of the SODCON survey. Rainfall in the period July 1992 to March 1994 has been 129 of the long-term average in East Anglia Anglia - a period of increased wetness of the same return period (16&200 (16&200 years) as the drought whic which h preceded it; therefore no inferences should be drawn about longterm domestic consumption from these data.

Toilets

Externa l use 3

Toilet

Washing machine 12 Luxury pp;y

32

w

7 nd Baths howers

Showers 4

Baths 13

SODCON DATA NOV 92 - OCT 93

Fig. 10. LCIWEM 1 9 9 5 ,9 , October

Miscellaneous 35

WATER FACTS 1992

Composition o f water use 485

 

EDWARDS AND MARTIN ON PROPERTY B

PROPERTY A

Washing machine hot

Dishwasher mld

2

Bath mid 5

I

19

2

TOTAL FLOW. 180 m3

Fig . 11 11..

TOTAL FLOW: 127 m3

Examples o f water use by ind ivi dual pr opert ies (November 19 1992 92-O -Octobe ctoberr 1993 1993))

TABLE II. AVERAGE OMPOSITION F NIGHT-TIMES E (OlO(M400 HOURS)

Washing machine Dishwasher Toilet Bath Showerioutside Showerioutsi de tap

49.9 29.9 19.5 0.6 Trace

The higher-than-expected evel of legitimate nightnighttime consumption led to h rthe rt he r analysis. Although Although the standard deviation of these results was high, as would be expected (since some houses use no water at night, and others use a considerable amount), the large sample size (1624 for this exercise) means that the standard stand ard error of the estimate is low (0.06 Vproperty Vproperty.. h), h) , and the sample sam ple mean lies lie s within 5 of the population mean with 95 confidence. n analysis of appliance use at night shows that washing machines use half of all water used (Table 11). An analysis of peak hourly flow indicates that the only appliance which has its peak flow at night is the dishwasher, which may indicate a correlation between between ownership of these appliances and use of economy electricity tariffs. Other appliances have their peak flows as might be expected from behavioural patterns (Table 111).

RELATIONSHIPS

The relationship between per capita consumption and the various parameters presented in Figs. 6-9 are providing useful infomation towards an understand486

ing of consumption patterns. The most significant factor is household size, which also affects the variability of per property consumption more than any other single sing le parameter. ACORN ACORN groupings indicate maximum PCC values in classes A (agricultural villages) and J (affluent suburban houses), and the lowest PCC is in ACORN class F (council) - all of which is not surprisin su rprising. g. The patterns of PCC against income and property R V also exhibit the expected trends, the higher consumption con sumption in the lowest RV band (less than &40pa) being due to the relativel relatively y highpe hig hperr capita consumption in small, s mall, low-RV properties occupied by by a single person.

EFFECTF METERINGN CONSUMPTION There is a wealth of opinion available on the effect of metering on consumption, but but there is very little evidence. Overseas studies offer a wide range of possibilities but their relevance to UK, let alone the Anglian region, is quesiionable. quesiio nable. The National Metering Trials reported reporte d that the effect eff ect ‘ranged from a slight increase to

TABLE IU. PEAKAPPLIANCE LOWS ND THEJR IMING

Appliance Total flow Washing machine Dishwasher Bath Shower Toilet Outside tap

Average peak flow

Timing of peak

32.0

08:15 10:45 03:15 18:45 07:30 OR00

(W 9.8

5.2 10.1 5.4 12.6

13:30

1.2 ~~

~

J CIW EM , 1995,9, October

 

A METHODOLOGY FOR SURVEYING DOMESTIC WATER CONSUMPTION

a fall of 17 ; the average reduction in use use was 1 ’(’). Evidence from SODCON has provided Anglian Water with a unique opportunityto develop robust robust estimates of the demand effect. It compares the consumption of approximates 1000 households who pay on a measured tariff with the consumption of the unmeasured SODCON households. The reported results (of an implied estimate estimate of 15 ) should be regarded regarded as preliminary, although they represent a considerable improvement upon estimates from elsewhere, and further work will be carried out as more information becomes available. WAY FORWARD

SODCON is already providing providing a vast amount of data for analysis, but some areas still need to be developed. There is a need to examine distribution losses, and SODCON can provide, through its water delivered data, excellent information on part of the water loss ‘balance’. Further work needs to be carried out to ensure compatibility between the meter readings on both research meters and the individual property meters. Having successfully measured domestic water consumption, monitoring sewage flows from properties is one logical step forward. A complex prototype sampler/monitor has been developed and tried by Anglian Water, but it now needs to be installed in sufficient ficie nt locations to provide representative data on net property water use. More applied research is needed to investigate the complicated inter-relationships between between consumption and such factors as weather, soil type, distribution water pressure and geographical location, and these analyses will be continued during the remaining years of the project. CONCLUSIONS

1. SODCON has already proved proved its worth in the quality of data which it has been able to provide. Domestic consumption levels, patterns and parameters which influence them them have been identified. Specific details such as night-time flows, keyappliance uses and combined flow-rates have been monitored and new areas of research have been indicated. 2 . The survey is also contributing significan significantly tly to providing a better service to Anglian’s customers. customers. The information is being used used as a tool to educate customers as to how water is used in the home and, by .implication, how how it can be conserved. A s an understanding of components of ‘waste’ and supply pipe and plumbing losses is being improved, advice can can be given to customers to improve the performance of their supply systems. Information from SOD.CIWEM 1995,9 , October

CON can also help customers to influence their own water bills. 3. The project’s greatest asset, however, is undoubtedly the enormous data base of (as yet) untapped information, which will be analysed and investigated in future yea years, rs, assisting in such tasks as longlongterm forecasting, tariff setting and demand management. REFERENCES (1) NATIONAL METERJNGRIALS ORKING ORKINGROUP. ROUP.Water Metering Trials: Final Rep ort. (Eds M. Hall and I. Kalsi.) WSA, WCA,

OFWAT, WRc and DOE, 1993. (2) HOOPER, . A survey of domestic water consumption in Devon and Comwall. Proc. Royal Statistical Society C o n f April 1979. (3) THACKRAY,. E., COCKER, V., AND ARCHIBALD, G. G. The Malvem and Mansfield studies of domestic water usage. Proc. Instn. Civ. Engrs. 1978,64, (l), 3 7 4 1 . ERVICES.9 981. 81. (4) CACI NFORMATION (5) MOORE,C. C. J. Personal communication.

DISCUSSION

Abridged) Mr R . Cook (Consultant), opening the discussion, asked if reference had been made to the ‘zonal metering’ studies which had been carried out by Anglian Water during 1975-76, and whether there was any merit in revisiting those locations to compare consumptions. Mr B. Hayes (Consultant) said that, in his opinion, the main benefit to Anglian Water would be the reduction in consumption of 15 , which would delay the nee need d for ccapital apital schemes. He enquired what the benefit to the customer would be, and wondered whether the company would be considering differential tariffs for night-time wat water er use. Mr S. Whipp (WRc Swindon) asked if SODCON had provided any information on the return period probability of specific levels of water consumption from groups of properties, which might place peak demands on the distribution system. Mrs C . Ridgewell (Essex and Suffolk Water) reque requested sted an outline of the methodology used to weight the SODCON sample results to provide a regional average figure for water consumption. Mr V . Ewan (Ewan Associates) Associates) asked whether the onginal premise of SODCON (i.e. that regional specifics necessitated a separate Anglian investigation of consumption) meant that the authors now believed that all water companies should undertake similar studies, or whether the Anglian data were transportable to other parts of the country. M r M. Pocock (Three Valleys Water) questioned the allowance made for underground supply pipe losses on the Tariff 1000 sample, which were used to derive the 1 5 reduction in consumption. Mr D. Evans (NRA) enquired when the authors auth ors would be able to provide estimates of consumptive use of water within the home, by means of their sewage flo flow w monitor. Mr J. Smithson (Mott MacDonald) wondered whether

the increased level of its night flowofwould that Anglian Water would change policy mainsmean rehabilitation as a result of this alteration to the economic balance. Mr E. Butt (Water Quality Management Ltd) asked if 487

 

A METHODOLOGYFOR SURVEYING DOMESTIC WATER WATER CONSUMPTION detailed consumption information information was given to the ‘Golden 100’ households if requested, and also whether the 2000 volunteers would be charged for their th eir water on a measured basis at any stage in the future, to examine the effect, if any, of such a change on domestic consumption. M r D. Ha rri s (Anglian (Anglian Water) Water) enquired enquired if the authors were satisfied with with the accuracy accur acy of the the meters in use, particpar ticularly when summated in the ‘Golden 100’ properties, and M r W. Davidson (also from Anglian Water) wondered if the detailed data available availabl e from SODCON could throw any light on problems of meter under-recording. M r M. Woolgar W S Atkins Ltd) asked if the ‘Golden 100’ properties propertie s were were fully ful ly representative of of the larger sample. He also enquired whether the difference in percentage water use by washing machines in the Anglian area, compared to ‘Waterfacts’ ‘Waterfacts ’ data for the country coun try as a whole, was related to ownership or usage variations.

In reply to Mr Cook, the a uth or orss said that that they had not not yet attempted any measurements measurements at the old zonal metering sites, largely due to their concern that the population base within the zones would undoubtedly have changed radically over the past 20 or so years. The turnover of volunteers in the SODCON study was about 7 per annum, therefore the applicability applicabil ity of the original locations lo cations and their data may not be great.

the data vindicated the use of the SODCON exercise within Anglian Water. Moreover, Moreo ver, because of this thi s level of detail, and and in particular particu lar the knowledge of the inherent variability of facfactors affecting consumption, they believed that it should be possible to apply the SODCON SODCO N database to other parts of the the UK and provide consumpti co nsumption on information with a high degree degree of confidence. The authors repeated that no n o allowance had been made for underground supply pipe losses on the 1000properties in in the tariff study, and acknowledged to Mr Pocock that such losses losses might, if undetected, affect the th e reduction in consumpt consumption ion thus estimated. It would, however, be relatively straightforward to carry out a simple test to verify this matter. The authors explained that Mr Evans would have to wai waitt several months mon ths for sufficient suffici ent samples to be collected co llected to be be able to answer his query. Given the probable higher degree degree of variability in i n water returned to sewer s ewer compared to water water delivered, it was possible pos sible that the standard error of the estimate would be high. Replying to Mr Smithson, the authors doubted whether this increase in night flow, although great in in percentage terms, would materially alter the rehabilitation programme, firstly since the effect on water delivered was was not yet proven and secondly because the prime driver for rehabilitation schemes was water quality, not quantity. Replying to Mr Butt, the authors confirmed that, on request, details of consumption patterns were sent to the ‘Golden 100’ volunteers. The transfer of customers from

Responding Respondi ng to Mr Hayes, they confirmed that any deferment of capital cap ital schemes would allow, ceterispparibus for a favourable favourab le effect on charges, which would certainly cer tainly benefit the customer. cu stomer. They commented that ‘intelligent’ ‘i ntelligent’ meters, capable of differential differe ntial charges according to the time of day, were being investigated by Anglian Water in a separate study to the SODCON project. In reply to Mr Whipp, the authors auth ors explained that they had yet to cany out this particular analysis. In answering Mrs Ridgewell, they said that the general technique was to examine the contribution to the variation v ariation of the dependent variable variable (consumption) provided by each of the independent variables (e.g. the socio-economic,household socio-economic,household size, and ACORN ACORN parameters which exhibited multi-collinearity) using stepwise multiple regression. Once the effect of each ‘independent’ variable was known, the results resul ts could be weighted to take into account variations in characteristics of the sample which would vary through time, to arrive (hopefully) at a

unmeasured to measured charges if SODCON volunteerss elected volunteer to be charged ondid thisoccur, basis; basis ; therefore this this effect could be monitored using the existing database, if necessary. The meters used in the survey were Class D (Schlumberger P40s and Kent PSMTs) PSMTs) or Class B (Andrae Leonberg) instruments, and the authors assured Mr Harris that they were confident that individual and cumulative accuracieswere accuracies were acceptable. The ‘square wave’ wave’ characteristic of flows through most point-of-use point-of -use meters meters certainly assisted assisted measurements; measurement s; there were relatively relativ ely small volumes passing passing at low flows. However, at this stage, the authors autho rs were were unable unable to provide Mr Davidson with any information on characteristics of under-recording of meters from the SODCON SODCON trials. In their reply to the final questions, the authors confirmed that the ‘Golden 100’ data were indeed representative o off the larger sample. sampl e. They considered that the greater use of washing machines in East Anglia was related both to the larger

stable estimate of PCC across the Anglian region as a whole. Responding to Mr Ewan, the authors felt that the detail of

market penetration of the appliance in the region and the great propensity of use.

Authors’ Reply

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J.CIWEM 1 9 9 5 ,9 , October