# Management information system (MIS)

Water Balance Calculations BASIC CALCUL ATIONS, COMMERCIAL AND PHYSICAL LOSSES Content Basic Water Balance Calculation Commercial Losses Physical Losses Summary 2 1. Basic water balance calculation IWA Water balance Billed authorised consumption Authorised consumption Unbilled authorised consumption Apparent losses (Commercial losses)

Total System Input Volume Billed metered consumption Billed unmetered consumption Revenue water Unbilled metered consumption Unbilled unmetered consumption Unauthorised consumption Metering inaccuracies Leakage in transmission and distribution lines Leakage and overflows at storage tanks Leakage on service connections up to customer meters Water losses Nonrevenue water

Real losses (Physical losses) WATER BALANCE CALCULATION 4 4 Basic NRW calculation [ ] = ( / = *Expressing NRW as a percentage of system input volume is a misleading and imprecise method, particularly in systems with

intermittent supply and very low operating pressures. However, percentages may be used when looking internally at the improvements made throughout a project WATER BALANCE CALCULATION 5 5 DMA Water Supply Input Volume The volume of water entering a DMA over a fixed period of time Calculated by: Physically reading the DMAs in- and outgoing meters at the start and end of a certain period (i.e. two weeks or one month) Analysing the flow data at the office (if meter fitted with GPRS / SMS) Try to coincide the period of time with the DMA billing period to be able to compare input volume with billed volume WATER BALANCE CALCULATION 6 DMA Billed Water The volume of billed water in a DMA over a fixed period of time Consumption Calculated by:

Billed volume taken from the monthly billing database Reading customer meters in a coordinated action Try and read the customer meters over the same period as the standard cycle DMA 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 05-01 Month Customer ID 12 12 12 12 12

12 12 12 12 12 12 12 12 12 12 12 10142370091 10202930229 10243320151 11011020010 11011020011 11011020020 11011020022 11011020029 11011020030 11011020040 11011020041 11011020050 11011020060 11011020070 11011020071 11011020075 Name

DOAN NGOC KHOA TRAN THI TUYET XINH VU HUY TU LAI SAN MIEN LUU HONG NGOC CHUA SUNG DUC NG NGOC SANG LE ANH TUAN CHENH A CAU NGUYEN AN MY NG BINH MINH DO TO TRAN AN TRAN LIEN CHIEU DUC NG THI HOANG HOANG VAN TAM Address DIEN BIEN PHU THANH THAI CC 830 SU VAN HANH PHU THO PHUTHO HONG BANG (SAN CHUA SUNG DUC) PHU THO PHU THO PHU THO

PHU THO PHU THO PHU THO PHU THO PHU THO PHU THO Water Last New Last Meter New Meter Days of Metered Meter reading Reading Read Date Reading Date Period Consumption Size 15 627 671 16/11/2011 15/12/2011 29 44 15 204 204 27/10/2011 28/11/2011 32 0 15 137 143 08/11/2011 08/12/2011 30 6 15 921 958 21/10/2011 21/11/2011 31

37 15 1345 1397 21/10/2011 21/11/2011 31 52 15 2407 2469 21/10/2011 21/11/2011 31 62 15 608 726 21/10/2011 21/11/2011 31 118 15 1189 1236 21/10/2011 21/11/2011 31 47 15 73 85 21/10/2011 21/11/2011 31 12 15 139 167 21/10/2011 21/11/2011 31

28 15 1106 1153 21/10/2011 21/11/2011 31 47 15 0 50 21/10/2011 21/11/2011 31 104 15 2415 2454 21/10/2011 21/11/2011 31 39 15 36 43 21/10/2011 21/11/2011 31 7 15 971 971 21/10/2011 21/11/2011 31 0 15 1052 1077 21/10/2011 21/11/2011 31

25 WATER BALANCE CALCULATION 7 International NRW assessment Category A1: potential for further NRW reductions is small Category A2: Further NRW reduction may be uneconomic Category B: Potential for marked improvements Category C: Poor NRW record; tolerable only if water is plentiful and cheap Category D: Highly inefficient; a comprehensive NRW reduction program is imperative and highpriority WATER BALANCE CALCULATION 8 2. Commercial losses Key components of commercial loss

COMMERCIAL LOSSES 10 Key components of commercial loss Water legitimately consumed but not billed, such as: Unbilled Authorised Consumption Water fountains; Pipe and sewer flushing; Watering parks and gardens; Public drinking fountains; Fire fighting hydrants Legitimate connections that were never entered into the billing system and are therefore never invoiced (intentional and accidental) Unauthorised Consumption Permanent or temporary meter bypass Illegal connections Illegal use of fire hydrants Volume under-recorded by revenue meter due to its condition Meter Inaccuracies Meter Reading Errors Over-sized revenue meters Meter tampering (water theft)

Corruption meter readers (collusion with customers) Meter reading errors (mistakes, or unreadable meters) Data handling errors billing department Accounting Errors Bills sent to wrong address COMMERCIAL LOSSES 11 Estimation of commercial loss Elements of commercial (apparent) water loss Commercial Loss Component Unbilled authorised consumption Billing errors Illegal connections Meter inaccuracy age Meter inaccuracy class Meter inaccuracy size Meter inaccuracy installation Meter inaccuracy tampering Data handling errors Data Source Data from billing department if metered (fire hydrants, pipe flushing, etc.) Thorough process analysis and analysis of billing data and database:

check billing database against actual meter readings; check GIS property number v actual property in DMA v billing database Check GIS property number v actual property in DMA v billing database Meter audit: test old meters (sample calibration) (on average meters under-read 5%) Meter audit: test class B or lower meters (sample calibration) Meter audit: check if meters are sized correctly Meter audit: check if meters are installed correctly Analyse information from meter reading / meter replacement team Meter reading audit COMMERCIAL LOSSES 12 3. Physical losses Key components of physical loss PHYSICAL LOSSES 14 Estimation of leakage in a DMA There are two methods to calculate the leakage volume in a DMA: 1.

Top-Down subtract the Commercial Losses from the NRW 2. Bottom-Up Measure the Minimum Night Flow and subtract the Legitimate Night Flow applying a pressure correction factor Top-Down method is easier to calculate, but less accurate as many of the Commercial Loss components are estimated Bottom-Up method requires complex measurement, but gives an accurate leakage figure Best practice is to use both methods and compare as a check PHYSICAL LOSSES 15 Estimation of leakage: top-down method To calculate an estimate of the physical losses, subtract the commercial losses from the NRW h =

[ PHYSICAL LOSSES ] [] [] 16 Estimation of leakage: bottom up Themethod Minimum Night Flow (MNF) is the lowest hourly average flow into the DMA over a 24-hour period, MNF is usually obtained between 2 and 4am, when most tanks have been filled and users are asleep The Legitimate Night Flow (LNF) is the customer minimum night consumption at the time of minimum night flow

Domestic customers toilet flushing, washing machines etc; use a standard legitimate night time factor, or measured sample Large nightly users (such as night clubs or industries) manually read or log their meter or use a portable meter The Net Night Flow (NNF) is the DMA leakage at the time of minimum night flow: what remains after subtracting the LNF from the MNF Some of the leakage occurs on the customers premises and therefore is not part of the utilities NRW. As such, the NNF should be divided into Utility leakage and Customer leakage PHYSICAL LOSSES 17 Estimation of leakage: bottom Identify the MNF (using a logged DMA meter) up method Identify the typical LNF Calculate the NNF = MNF LNF

Estimate the Utility leakage UNNF = NNF Customer leakage As leakage is proportional to pressure, to represent the average leakage through the day the UNNF should be corrected with a pressure factor (pf), typically pf = average daily DMA pressure / average MNF pressure Average DMA leakage = UNNF*pf Peak demand = lowest DMA pressure = lowest level of daily leakage Night demand = highest DMA pressure = highest level of daily leakage Legitimate Customer Night Use Minimum Night Flow PHYSICAL LOSSES Varying Customer Demand

Leakage Varying with DMA Pressure throughout the Day 18 Estimation of leakage: bottomup method Minimum Night Flow into DMA (MNF) = 13 m3/hour Number of domestic connections in DMA = 500 Average DMA occupancy rate =5 Legitimate Domestic Night Use factor1 = 1.7 litres / person / hour Legitimate Domestic Night Use = 500 x 5 x 1.7 / 1000 = 4.25 m3/hour Measured Exceptional Night Use = 1 m3/hour

Night leakage (L0) = 13 4.25 1 = 7.75 m3/hour Measured night pressure (P0)) = 25 metres Measured average DMA pressure (P1) = 15 metres Therefore average DMA leakage (L1) = 7.75 x (15/25) = 4.65 m3/hour Or, average DMA leakage (L1) = 111,6 m3/day 1 IWA Standard Factor Compare this result with the result of the Top-Down calculation PHYSICAL LOSSES 19

4. Summary Water balance calculations In order to understand NRW quantitative as well as qualitatively, it is essential to make a calculation of the water balance: the ratio of water produced to water sold While making the water balance, where possible, one should distinguish between the different causes of water loss: technical, administrative, illegal consumption, authorised consumption, etc. Depending on the resources available on can make water balance calculations in different ways The basic NRW calculation is easy, but gives only information on the total level of NRW. The outcome can be used to make an international comparison on NRW performance Estimates can be made of commercial losses by thoroughly studying the customer billing database and by field surveys Physical loss can then be calculated using total physical loss (top-down) or by more detailed field study (bottom up) SUMMARY 21

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