"Top-down„ approach is a faster, cheaper and simpler, but less accurate, unlike the approach of "bottom-up" which is based on hydraulic measurement, which is more expensive, more complex and more precise.

Further are described a methodology for managing with water balance using “bottom – up” approach.  

Before Starting

A certain number of decisions have to be made before initiating the Water Balance calculation.  All factors that affect the reliability of this study shall be discussed in the following subsections:

Water Balance Table

For the purpose of Water Balance it is necessary to prepare a worksheet table.   Software for Water Balance calculation using “bottom-up” approach can be downloaded from this website and named CalcuLEAKator.  

Methodology described represents a basic Water Balance and every following analysis shall be based on it. 

Within this analysis it is necessary to do the following:

• Verify and update system maps
• Test main meters as well as the source meters
• Verify and update water inflow records, records on metered consumption (e.g. billing data), unmetered consumption (also including consumption estimations for parks, community centres, state-owned objects and firefighters)
• Test the accuracy of water meters for households, legal entities and industry
• Test metering devices, i.e. their dimensions, installation accuracy and operational regime
• Convey site investigations of distribution and operational procedures of the system or performed water leaks measurement in DMAs.

All above activities are being carried out by implementing a step by step method.

 Activity 1 – Metering Water Inflow into the System

This activity shall help us find out what volume of water is entering the system and where that water comes from, which represents a basis for the definition of each indicator and is being carried out in accordance with the following steps:

Step 1-1 Source Identification and Mapping

If the existing maps are updated and contain zone borders, reservoirs, pumping stations, data on pipelines, key valves and large meters, than they could be used as a basis for initiating the Water Balance activities.  Over time, during the course of this analysis and the analyses that follow, it is necessary to complete the maps.  Currently, precise GPS devices are available and enable the recording of data on site and their direct input into the GIS.  Also, a possibility of exchanging and taking maps from other utility companies in the territory of the respective municipality should be taken into consideration.

Within this step it is essential to visit each source and identify the type of equipment used on that particular source.  At the source, basic information on metering equipment, including its type, ID number, reading frequency, recording type, unit of measurement, installation date, pipe profile, testing frequency and date of last calibration are being recorded.

Also, total water inflow from each source is being recorded, and the total uncorrected volume of water produced at all sources calculated.

Step 1-2 Water Measurements at Each Source

The target is to calculate and record total water inflow from each source and calculate the total volume of water produced at all sources during the course of the study. 

For that purpose, it is necessary to do the following:

• Inspection of objects at the sources
• Review of water production records
• Inspection of pumping stations
• Control of records on flows at reservoir inlets and outlets
• Identify problems at influent pipelines
• Identify volume of unmetered water consumed during the filter maintenance process
• Determine the cost of elements being a part of water production costs (chemicals, el. energy and alike)
• Test all meters at the sources and pumping stations (if there are any) during their typical operation mode, including different combinations of pump operation.  Elaborate recommendations with necessary corrections to be made in order to improve meter readings.

Step 1-3 Harmonization of Parameters Relating to Water Inflow into the System

Parameters relating to the total inflow of water into the system are based on the readings of meters and measurement instruments and represent raw data which within this step must be adjusted by taking into consideration meter inaccuracy, water level fluctuations in the reservoirs, unmetered volume of water and losses before water system inflow point etc. 

Activity 2 – Metering of Authorized Metered Consumption

Authorized water represents all water that is being used for all purposes authorized by the utility.  Most of authorized water is metered, however not all of it.  Metered water which is mostly being sold to the customers includes industrial, commercial, residential, agricultural and governmental consumption.

Unmetered authorized consumption is also relating to the extraordinary public consumption such as street washing, park irrigation, graveyard maintenance or fire extinguishment.

For the purpose of determining the volume of authorized consumption it is necessary to perform detailed analysis of two categories of authorized consumption such as:

Step 2-1 Identification of Metered Consumption

All customers whose water consumption is metered and who are being delivered water bills based on metered consumption fall into this group.  

Data is taken from Utility’s Accountancy Dept. and a list with zone consumption is prepared (in case of large water utilities – over 5 000 connections) or a list with customer groups and zones (in case of smaller water utilities).  Based on this data, an administrative identification of all zone customers with water meters is performed, and a list of all active connections containing an ID number, type and water meter profile data is prepared.        

Perform a detailed analysis of all 50 mm or bigger water meters.  This analysis is designed in a way to help identify inconsistencies inside the water meter or during the billing cycle, as well as to determine potential metering errors resulting from a wrong selection of water meter profile and the way it was used.  

The analysis includes a review of a certain number of small water meters and making of the old water meter replacement schedule based on age, type and quality of the water meter and the water itself.

Step 2-2 Metering of Metered Consumption

Based on identified metered consumption all water consumption is being calculated.  Within the scope of the top-bottom analysis, the calculation is being made in accordance with the identified metering zones, and within the analyses that follow it is being elaborated in details so as to systematize connections per water meter size on a monthly basis (or some other billing period) during the whole course of the study.      

When flow meter reading dates do not overlap with the starting and ending date of the Water Balance study, it is necessary to make metered consumption data corrections.

Step 2-3 Metered Consumption Data Adjustment

Considering the fact that almost each Utility has a huge number of customer water meters, it does not pay off to check and test each and every one of them every year.  Instead, testing of all 50 mm or bigger water meters is being performed (test in place), while the control of smaller water meters in different zones is performed randomly.

Activity 3 – Metering of Authorized Unmetered Consumption

The volume of unmetered water has to be carefully estimated in order to perform an accurate water balance.  This activity includes a description of the manner in which the water that is consumed and not metered is being metered.  While selecting the best procedures for the aforementioned situation, difficulties during data collection, required accuracy level, potential availability of equipment, staff training level etc. should be taken into consideration.

Step 3-1 Identification of Authorized Unbilled Unmetered and Metered Consumption

A large number of water utilities enable authorized but unmetered water consumption.  This is typically called “authorized non-presented water consumption”.  Unmetered water consumption can include the training for fire extinguishment and the extinguishment itself, flushing of storm channels, street washing, irrigation of large public areas, public taps and fountains, pools, buildings etc.    

Step 3-2 Assessment of Authorized Unbilled Unmetered and Metered Consumption

In order to make an assessment of the total unmetered water consumption, the total amount has to be divided into different consumption categories (training for fire extinguishment and the extinguishment itself, flushing of storm channels, street washing, irrigation of large public areas, public taps and fountains, pools, buildings etc).

Activity 4 – Nonrevenue Water (NRW)

This activity shall show how much water is being lost into the distribution system and what percentage is being attributed to leakages.

Step 4-1 Identification of Potential Water Losses

The highest portion of losses could be attributed to the following causes:

• Calculation mistakes
• Unauthorized connections
• Inadequate system control
• Reservoir leaks
• Evaporations
• Reservoir overflows
• Unauthorized water consumption
• Detected leaks
• Other leaks

 Step 4-2  Loss Assessment

Within this step an assessment of losses due to previously identified causes is made: 

• Calculation mistakes
• Unauthorized connections
• Inadequate system control
• Reservoir leaks
• Evaporations
• Reservoir overflows
• Unauthorized water consumption
• Detected leaks
• Other leaks

Step 4-3   Flow and Pressure Measurement: Balance Method and Night Measurement Method

Loss measurement is performed by zones with the application of Balance Method and Night Measurement Method in a way described in the text bellow.  The aforementioned methods entail that the water system is under pressure.  Measurement results obtained by applying both methods are being consolidated and analysed.  

Step 4-4  Detect and Remove Redundant Pipes and Illegal Connections

Data on volume of unmetered water and the number of illegal connections is estimated based on the number of detected illegal connections during one year or based on the experience of the staff of the Utility.  That information is used in order to determine the percentage of unauthorized unbilled consumption.  Based on the information gathered it is important to accurately locate and eliminate all unnecessary pipes so as to be able to clearly define an area.  Pipe removal entails either physical disconnection or valve installation at both ends of unnecessary pipes, in case there is no connection along the pipe.  Pipe disconnection minimized the risk of losing water along the disconnected lines.  Documentation for the utility together with the instructions for system operation – i.e. which valves are to be opened or closed, is prepared for each planned intervention.

During the course of this activity referring to the disconnection of unnecessary pipes, the pressure in the system is being monitored.  If the intervention described would cause a significant pressure drop which would negatively affect the customers, an outlet gate valve is to be installed at certain points.  With the use of ultrasonic flow meter, water flow shall be registered as inflow if the water enters the service area or as outflow if it flows out of the service area.  If the flow is variable, 24 hour monitoring is performed, and if there are fluctuations also during the day, than 7 day measurement is performed.  Depending on the results obtained, with the aim to improve water supply, installation of additional pressure reducers and air valves is proposed so as to enable air release from the pipes and thus prevent the damaging of the pumps, pipes and fittings.  Interventions such as physical destruction or removal of existing pipes should be avoided.  All interventions must be made while taking into consideration the impact on adjacent areas.  All interventions must be carried out in accordance with the local laws, and all activities that require excavations or access to the manholes and valve manipulation have to be coordinated with the water utilities.  All key valves must be tested to the street connection level.  In order to verify isolation from the rest of the water system, short interruption of water inflow into the zone is caused by manipulating the main valve(s) so as to observe pressure drop.   In case there are doubts that the zone is supplied with water through undocumented pipe (there was no abrupt pressure drop once the main valve(s) was/were closed), physical location of such pipe has to be performed.

In order to estimate the number of illegal connections, the number should be compared with the number of residential units and the number of registered connections in the same administration unit.  So as for the records to be complete, the possibility of secondary water sources should be investigated (e.g. open boreholes, springs).  In parallel, customer survey is being carried out with the aim to identify the nature of water consumption (e.g. water for the purpose of drinking, washing, flushing toilets, garden irrigation, filling the pools and alike).  This data, in combination with registered customers’ real water meter readings enables extrapolation and the calculation of total water consumption in the zone or in the overall system.  The difference between consumption and registered consumption shall make possible for the quality assessment of the number of illegal connections to be made.

By performing the analysis of historical data it could be focused on specific areas deemed to have highest losses.  These analyses are of critical importance for defining the consumption, analysing the reduction in water consumption, study of water losses, water meter sizes and their application, as well as for hydraulic modelling and elaboration of the master plan.

Step 4-5  Billing Data Analysis

Mistakes during billing process could be avoided by performing software data analysis which would automatically monitor unusual customer behaviour such as sudden increase of decrease in consumption, among others.  In the event of meter inaccuracy, a formula for the calculation of water consumption based on earlier readings, period of the year and the number of household members is recommended.

Step 4-6  Asset Management Analysis

Site investigations, data collection and analysis and discussion on the policies, practices and preconditions relating to the asset management shall be held with the staff of the utility. This activity shall include:

• Pipe replacement and repair policy and practice    and
• Facility operation and maintenance policy and practice

 Activity 5 – Analysis of Water Balance Results

Balance results could indicate losses resulting from inaccurate metering, unauthorized consumption, reservoir, main pipe or connection service pipe leaks.  In order to determine what necessary correction measures are cost-effective, first we have to estimate leaks that could be repaired, as well as the costs of their repair.  Within this analysis, based on the Water Balance indicator values obtained, conclusions are being drawn and recommendations given.

If the value of “saved” water exceeds leak repair costs, than carry out a measurement program, as well as leak detection and leak repair programs.

Step 5-1 Identification of Repairable Leaks

Not all leaks can be repaired.  Earlier in the text it was described that there is a UARL indicator which represents an unavoidable loss.  In order to determine the percentage that could be repaired, first we have to find out what the total leak percentage is, and then determine what percentage could be repaired. 

Step 5-2  Repaired Leak Value Determination

Saving water saves many.  What costs could be saved if the leaks are prevented?

There are two types of saving:

• Water procurement costs     and
• Variable O&M costs relating to water storage, treatment and distribution.

Neither case includes fixed costs.  Savings equal the value of leaks repaired.  

Step 5-3 Leak Repair Cost Determination

This step includes two parts:

• One-year benefit – in order to identify leak repair benefits during one year, multiply repaired leaks by leak repair costs
• Two-year benefit – average leak duration before repair is estimated at two years, mostly depending on the pipe and soil condition, as well as the quality of the leak detection program

Step 5-4 Leak Detection Cost Calculation

Costs of conducting leak detection are estimated by preparing leak detection and repair program.  

Activity 6 – Report

Upon the finalization of the Water Balance, a report is being prepared as well as the presentation, if necessary.

The report should include the following:

• Water Balance with the presentation of indicators used for the calculation of ”non- revenue water” and the presentation of 5 key indicators in accordance with IWA’s methodology
• Overview and presentation of information gathered
• Comprehensive analysis of current situation
• Overview of measures and activities essential for water loss reduction and improvement of water distribution system maintenance, accompanied by cost projection 
• Analysis of economic indicators for planned future activities with the aim of reducing losses (overview of expected savings), preferably in a form convenient for potential loan application 
• Final report shall be fully harmonized with IWA’s recommendations

The final report shall present basis for the elaboration of NRW management strategy and its future implementation.  

In the upcoming course of the Water Balance analysis, a difference between the volume of water produced and the volume of authorized water consumption is calculated by which the value of total losses in the system, or the so-called “non-revenue water” is obtained.    

Total water losses are then being divided into two recognized categories:

Apparent (Commercial) Losses

Apparent losses include all types of illegal water consumption as well as metering errors referring to all types of meters in one system.

Real Losses

Real losses include all kinds of leakages, pipe bursts, reservoir leaks, water transport through private property to the customer’s water meter and alike.

Water Balance also tests and analyses water collection rate in proportion to the metered consumption, accuracy of large water meters, pump efficiency and economic loss analysis.   

Customer water supply has the highest importance ever, because water treatment, storage and pumping with the installation of cost increasing infrastructure and reduced water resources, result in the increase of responsibility on behalf of the responsible people in the Utility in reference to each element of the system, from the source to the customer.