Melbourne
Water resources and systems

The following set of notes provides consolidated reports for each of the water stores and systems within the Melbourne region during the 2011–12 year. The water stores and systems included in the region are shown in Figure 1.

For more information about the region, please refer to the General description section of the 'Contextual information'.


Figure 1  Schematic diagram of water stores and systems within the Melbourne region

Information on all water flows to and from each water store and system are presented in this note, including between-store flows and transfers that are not presented in the water accounting statements. The between-store flows and transfers that occur in the region are presented in Figure 2.

The numbers on the diagram refer to the line item numbers in the water store notes. For each between-store flow, there are two line item numbers: one refers to flow out of a water store and the other refers to flow into a water store.


Figure 2  Schematic diagram of between store flows that occur within the Melbourne region. Line item numbers are provided next to the flows.

The between-store flows and transfers (Figure 2), which are eliminated from the region's water accounting statements, are shown in italics throughout the following set of notes. The allocation announcement, forfeiture and allocation remaining line items associated with each between-store abstraction (brown arrows in Figure 2) are also shown in italics in the following notes.

A description of the Melbourne region's surface water resources is provided in the Surface water section of the 'Contextual information'.

The Statement of Water Assets and Water Liabilities for the surface water store (Table 1) shows that total surface water assets and net water assets increased during the 2011–12 year in the Melbourne region.

Table 1  Statement of Water Assets and Water Liabilities for the surface water store

Water assets	Volume at 30 June 2012 (ML)	Volume at 30 June 2011 (ML)
1 Surface water
1.1 Storages	686,630	671,747
1.2 Unregulated river	–	–
1.3 Regulated river	–	–
1.5 Inter–region claim on water	693,212	456,494
1.7 Claim on desalinated water	0	0
Total surface water assets	1,379,842	1,128,241
Water liabilities
5 Surface water liability
5.1 Surface water allocation remaining	0	0
5.2 Surface water allocation remaining – urban water system	588,618	582,445
5.4 Inter–region commitment on surface water	0	0
Total surface water liabilities	588,618	582,445
Opening net water assets	545,796	625,183
Change in net water assets	254,428	(79,387)
Closing net water assets	791,224	545,796

The volume of water in unregulated rivers (line item 1.2) and regulated rivers (line item 1.3) could not be quantified due to a lack of available data.

The location of each storage within the Melbourne region, and the volume of water in each storage (including dead storage) as a percentage of total storage capacity at the end of the 2011–12 year, is shown in Figure 3.

Figure 3  Location map of the storages within the Melbourne region. The % full volume on 30 June 2012 for each storage is also shown.

The surface water storage volume within the Melbourne region increased marginally during the 2011–12 year (from 78% to 80%); this was reflected by small increases or decreases in storage volumes across the region. With the exception of Tarago Reservoir, storage volume within the Melbourne region was greater than 70% of capacity as at 30 June 2012 (Figure 3).

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the surface water store are provided in Table 2 and Table 3, respectively.

Table 2  Statement of Changes in Water Assets and Water Liabilities for the surface water store

Water asset increases	2011–12 volume (ML)	2010–11 volume (ML)
9 Surface water increases
9.1 Precipitation on surface water	48,406	53,802
9.3 Groundwater discharge	–	–
9.4 Runoff to surface water	2,897,235	3,944,083
9.5 Point return from irrigation scheme	77	51
9.9 Discharge from urban water system	12,161	15,390
9.10 Direct discharge by user	–	–
9.15 Increase of inter–region surface water claim on water	259,701	262,417
9.17 Increase of surface water claim on desalinated water	0	0
Total surface water increases	3,217,580	4,275,743
Water liability decreases
13 Surface water liability decreases
13.1 Adjustment and forfeiture of surface water allocation	10,636	12,903
13.2 Adjustment and forfeiture of surface water allocation – urban water system	45,156	0
13.4 Adjustment and forfeiture of inter–region commitment on surface water	0	0
Total surface water liability decreases	55,792	12,903
Water asset decreases
17  Surface water decreases
17.1 Evaporation from surface water	42,190	36,087
17.2 River outflow from the region	1,918,282	2,502,127
17.3 Leakage to groundwater	–	–
17.4 Leakage to landscape	–	–
17.6 Surface water diversions – other statutory rights	–	–
17.7 Entitled diversion on non–allocated surface water to users	17,571	16,883
17.17 Decrease of inter–region surface water claim on water	20,791	10,084
17.19 Decrease of surface water claim on desalinated water	0	0
Total surface water decreases	1,998,834	2,565,181
Water liability increases
21 Surface water liability increases
21.1 Surface water allocation announcements	20,761	19,521
21.2 Surface water allocation announcements – urban water system	425,527	937,686
21.4 Increase of inter–region commitment on surface water	3,040	3,168
Total surface water liability increases	449,328	960,375
Balancing item – surface water	579,782	842,477
Change in net water assets	254,428	(79,387)

Table 3  Statement of Water Flows for the surface water store

Water inflows	2011–12 volume (ML)	2010–11 volume (ML)
9 Surface water inflows
9.1 Precipitation on surface water	48,406	53,802
9.3 Groundwater discharge	–	–
9.4 Runoff to surface water	2,897,235	3,944,083
9.5 Point return from irrigation scheme	77	51
9.9 Discharge from urban water system	12,161	15,390
9.10 Direct discharge by user	–	–
9.11 Delivery of water under inter–region agreement to surface water	2,192	20,376
9.13 Delivery of claimed desalinated water to surface water	0	0
Total surface water inflows	2,960,071	4,033,702
Water outflows
17 Surface water outflows
17.1 Evaporation from surface water	42,190	36,087
17.2 River outflow from the region	1,918,282	2,502,127
17.3 Leakage to groundwater	–	–
17.4 Leakage to landscape	–	–
17.6 Surface water diversions – other statutory rights	–	–
17.7 Entitled diversion on non–allocated surface water to users	17,571	16,883
17.11 Entitled diversion of allocated surface water to users	10,125	6,618
17.12 Entitled diversion of allocated surface water to urban water system	374,198	355,241
17.14 Surface water transfer under inter–region commitment	3,040	3,168
Total surface water outflows	2,365,406	2,920,124
Balancing item – surface water	579,782	842,477
Opening water storage	671,747	400,646
Add/(Less): Change in water storage	14,883	271,101
Closing water storage	686,630	671,747

A schematic diagram representing all the inflows and outflows associated with the surface water store in the Melbourne region is provided in Figure 4. The numbers in brackets on the diagram refer to the line item numbers in Table 3.


Figure 4  Schematic diagram of water inflows and outflows for the surface water store within the Melbourne region during the 2011–12 year. Line item numbers are provided in brackets.

Table 3 shows that surface water storage increased during the 2011–12 year by 14,883 ML, despite declining inflows to the surface water store compared to the 2010–11 year. The maintenance of high surface water storage volumes across the Melbourne region is primarily attributed to the continuation of above average rainfall conditions across the region (refer to the Climate overview section of the 'Contextual information') and the fact that inflows were still considerably greater than outflows during the 2011–12 year.

Surface water diversions

The majority of diversions from surface water are for the urban water system (line item 17.12), which accounts for more than 90% of total surface water diversions. Diversions to Melbourne's irrigation districts and private take and use licence holders makes up the remaining surface water diversions.

During the 2011–12 year diversions to the urban water system, irrigation districts and private licence holders increased compared to the 2010–11 year. Although rainfall across the entire Melbourne region was above average for the 2011–12 year, this contrasted with very much above average rainfall for the 2010–11 year, likely reducing demand and subsequently surface water diversions during the 2010–11 year.

Diversions to the irrigation districts and the urban water system are associated with a water access entitlement.

For the irrigation districts, when an allocation is announced, a present obligation (water liability) is created on the surface water to deliver water to the users. As there is no carry-over provision for the irrigation district's water shares, the portion of the announced allocations that were not diverted by the end of the year was forfeited.

For the urban water system, the retail water authorities hold several bulk entitlements that entitle them to a share of storage capacity in reservoirs across the region. This share of storage may increase due to inflows and runoff (line item 21.2) and decrease due to evaporation, operational losses and spills (13.2).

The entitlement, allocation announcement and forfeiture for each of these water rights during the 2011–12 year are provided in the Surface water rights section of the 'Water access and use' note.

The balancing item volume represents the difference between the measured opening and closing balances of the surface water store, after physical inflows and outflows have been applied. This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete surface water store balance.

Table 4  Balancing item for the surface water store for the 2011–12 year

	Account	Volume (ML)
	Opening balance (30 June 2011)	671,747
add	Total surface water inflows (see Table 3)	2,960,071
less	Total Surface water outflows (see Table 3)	2,365,406
less	Closing balance (30 June 2012)	686,630
	Balancing item – surface water store	579,782

The calculation of the water balance on the surface water store yielded a balancing item of 579,782 ML. This is approximately 85% of the total surface water store volume at the end of the 2011–12 year and around 20% of the total surface water inflows during the 2011–12 year.

It is likely that the balancing item is primarily attributed to errors associated with the rainfall runoff, a large source of surface water increase (line item 9.4). The rainfall runoff volume is derived from a rainfall-runoff model and it is reasonable to expect a 10–20% uncertainty around the modelled runoff volume (+/– 580,000 ML). As a consequence the modelled runoff is likely to be an overestimate of the volume that actually entered the surface water store.

A description of the Melbourne region's groundwater resources are provided in the Groundwater section of the 'Contextual information'.

The volume of groundwater assets remained constant during the 2011–12 year (Table 4). This was due to the quantification approach of the groundwater assets (refer to line items 2.1 Water table aquifer and 2.2 Underlying aquifers). 

The Statement of Water Assets and Water Liabilities for the groundwater store is shown in Table 5.

Table 5  Statement of Water Assets and Water Liabilities for the groundwater store

Water assets	Volume at 30 June 2012 (ML)	Volume at 30 June 2011 (ML)
2 Groundwater
2.1 Water table aquifer	21,873	21,873
2.2 Underlying aquifers	16,565	16,565
Total groundwater assets	38,438	38,438
Water liabilities
6 Groundwater liability
6.1 Groundwater allocation remaining	0	0
6.2 Groundwater allocation remaining – urban water system	0	0
Total groundwater liabilities	0	0
Opening net water assets	38,438	38,438
Change in net water assets	0	0
Closing net water assets	38,438	38,438

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the groundwater store are provided in Tables 6 and Table 7, respectively.

Table 6  Statement of Changes in Water Assets and Water Liabilities for the groundwater store

Water asset increases	2011–12 volume (ML)	2010–11 volume (ML)
10 Groundwater increases
10.1 Groundwater inflow from outside region	0	0
10.2 Groundwater inflow from outside region at coast	280	1,113
10.3 Recharge from landscape	552,266	877,331
10.4 Recharge from surface water	–	–
10.6 Leakage from urban water system	28,352	25,715
Total groundwater increases	580,898	904,159
Water liability decreases
14 Groundwater liability decreases
14.1 Adjustment and forfeiture of groundwater allocation	28,353	29,186
14.2 Adjustment and forfeiture of groundwater allocation – urban water system	412	401
Total groundwater liability decreases	28,765	29,587
Water asset decreases
18 Groundwater decreases
18.1 Groundwater outflow to outside region	0	0
18.2 Groundwater outflow to outside region at coast	121,259	129,345
18.3 Discharge to landscape	42,546	16,516
18.4 Discharge to surface water	–	–
18.7 Groundwater extractions – other statutory rights	–	–
18.8 Entitled extraction of non–allocated groundwater to users	–	–
Total groundwater decreases	163,805	145,861
Water liability increases
22 Groundwater liability increases
22.1 Groundwater allocation announcements	41,526	39,370
22.2 Groundwater allocation announcements – urban water system	412	413
Total groundwater liability increases	41,938	39,783
Balancing item – groundwater	403,920	748,102
Change in net water assets	0	0

Table 7  Statement of Water Flows for the groundwater store

Water inflows	2011–12 volume (ML)	2010–11 volume (ML)
10 Groundwater inflows
10.1 Groundwater inflow from outside region	0	0
10.2 Groundwater inflow from outside region at coast	280	1,113
10.3 Recharge from landscape	552,266	877,331
10.4 Recharge from surface water	–	–
10.6 Leakage from urban water system	28,352	25,715
Total groundwater inflows	580,898	904,159
Water outflows
18 Groundwater outflows
18.1 Groundwater outflow to outside region	0	0
18.2 Groundwater outflow to outside region at coast	121,259	129,345
18.3 Discharge to landscape	42,546	16,516
18.4 Discharge to surface water	–	–
18.7 Groundwater extractions – other statutory rights	–	–
18.8 Entitled extraction of non–allocated groundwater to users	–	–
18.11 Entitled extraction of allocated groundwater to users	13,173	10,184
18.12 Entitled extraction of allocated groundwater to urban water system	0	12
Total groundwater outflows	176,978	156,057
Balancing item – groundwater	403,920	748,102
Opening water storage	38,438	38,438
Add/(Less): Change in water storage	0	0
Closing water storage	38,438	38,438

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Melbourne region is provided in Figure 5. The inflow and outflow volumes for the groundwater store during the 2011–12 year are given in Table 7. The numbers in brackets on the diagram refer to the line item numbers in Table 7.



Figure 5  Schematic diagram of water inflows and outflows for the groundwater store within the Melbourne region during the 2011–12 year. Line item numbers are provided in brackets.

Allocations and extractions

Most of the extractions from the groundwater store were for licensed private use (18.11 Groundwater allocation extraction). In general, extractions from groundwater increased marginally compared to the 2010–11 year. This increase is consistent with the increase observed in surface water diversions, primarily attributed to the fact that the 2010–11 year was a very wet year, reducing demand on water resources for all water users.

The allocation extractions are all associated with a water access entitlement. When an allocation is announced, an obligation (water liability) is created on the groundwater to deliver water to the users. As there is no carry-over provision in the region, the portion of the announced allocations that was not diverted by the end of the year was forfeited.

The entitlement, allocation announcement and forfeiture for these water rights during the 2011–12 year are  provided in the Groundwater rights section of the 'Water access and use' note.

The balancing item volume represents the difference between the measured opening and closing balances of the groundwater store, after physical inflows and outflows have been applied.

The balancing item is calculated according to Table 8.

Table 8  Balancing item for the groundwater store for the 2011–12 year

	Account	Volume (ML)
	Opening balance (30 June 2011)	38,438
add	Total groundwater inflows (see Table 7)	580,898
less	Total groundwater outflows (see Table 3)	176,978
less	Closing balance (30 June 2012)	38,438
	Balancing item – groundwater store	403,920

The calculation of the water balance on the groundwater store yielded a balance difference of 403,920 ML, approximately 70% of the total groundwater inflows during the 2011–12 year. 

The groundwater asset in the Melbourne region is equivalent to the legal extractable limit and does not reflect fluctuation of groundwater levels over time. Therefore, groundwater assets for the region are not responsive to groundwater storage changes resulting from water table fluctuations. As a result, estimated inflows and outflows are more appropriately compared to the change of water stored in the aquifers than to the opening and closing balance of the groundwater asset.

The volume reported as the balancing item for the groundwater asset is considerably less than that reported for the 2010–11 comparative year (741,083 ML). During the 2010–11 year, total groundwater inflows were very large. This large increase in recharge reflected the well above average rainfall conditions observed throughout the region in the 2010–11 year. While above average rainfall conditions persisted during the 2011–12 year, these conditions were substantially drier than the 2010–11 year.

The change in aquifer storage was calculated using groundwater levels for the water table aquifer within the sedimentary area identified in Figure 6. The groundwater levels were estimated using all bores within the region, assuming that all hydrogeological layers are hydraulically inter-connected.

Figure 6  Map of water table aquifer within the sedimentary area used to calculate aquifer storage

The change in storage for water table aquifer in the Melbourne region during the 2011–12 year was estimated at 46,692 ML. This increase in storage was considerably less than that of the 2010–12 year (Table 9).

Table 9  Change in aquifer storage estimate for the 2011–12 and 2010–11 years

Management area	Change in storage 2011–12 (ML)	Change in storage 2010–11 (ML)
Clipped sedimentary areas	46,692	208,284

Because the aquifers included in the calculation of the change in aquifer storage represent only a fraction of the groundwater resources in the Melbourne region, the value in Table 9 only partially reflects the difference between inflows and outflows shown in Table 7.

Data source

Port Phillip Catchment Management Authority: groundwater model (Department of Sustainability and Environment 2010b), hydraulic conductivity and aquifer thickness; Victorian Department of Environment and Primary Industries: bore locations, groundwater level data and aquifer attribution.

Data provider

Bureau of Meteorology.

Method

Change in extractable storage is estimated using a simple geographic information system (GIS) approach based on measured groundwater levels and aquifer properties. Firstly, groundwater levels are estimated at the start (1 July 2011) and the end (30 June 2012) of the 2011–12 year. This is achieved by considering all groundwater level measurements between March 2011 to October 2011 and March 2012 to October 2012, respectively, and using the measurements closest in time to interpolate the start and end levels.

The estimated groundwater levels on the start and end dates are then spatially interpolated to grids using the ArcGIS Topo-to-Raster tool. The interpolated groundwater level surfaces at the start and the end of financial year and the interpolated change in groundwater level at each bore are then used to calculate the change in volume between them within the sedimentary area. Finally, these volumes are multiplied by appropriate specific yield values to convert to a change in groundwater storage and masked for areas within 10 km of a groundwater observation bore. The average of these volumes is reported.

Uncertainty

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (example: groundwater levels, specific yield) was not specified and hence the impacts of such uncertainty on the change in storage is not estimated.

The change in storage estimations were based on interpolated groundwater level grids produced using the ArcGIS Topo-to-Raster tool. Use of other interpolation methods may impact the values of the groundwater level grids and hence the estimated values for change in groundwater storage.

Approximation, assumptions, caveats and limitations

The groundwater levels were estimated by assuming that all the hydrogeological layers (excluding basement) within the Port Phillip and Western Port groundwater model region are hydraulically inter-connected. This assumption facilitates the interpolation of a groundwater potential surface from groundwater level measurements as these measurements were limited in number.

Groundwater levels are assumed equal to zero metres Australian Height Datum (mAHD) at the coastline.

Change in groundwater storage was not calculated for confined aquifers. The annual change in storage was considered to be negligible for confined aquifers due to their very low storativity, which is much lower than the specific yield of unconfined aquifers (Freeze and Cherry 1979). Upon lowering of water levels in such aquifers, they remain fully saturated so that no dewatering occurs. The water diverted is volumetrically equivalent to the volumetric expansion of the water and contraction of the pore space.

Annual change in storage in fractured bedrock is considered negligible as these systems typically have a low specific yield. Furthermore, groundwater extraction in fractured rock areas is limited in volume.

The spatially varying specific yield values considered in the Port Phillip and Western Port groundwater model are used in these estimations.

A 10 km buffer around bores was used to acknowledge the spatial variability of groundwater levels and the density of  the data available. Outside the buffer the storage is considered constant through the year to reflect the no data availability.

The urban water system within the Melbourne region is discussed in the Other water resources and systems section of the Contextual information.

Volumetric information relating to the urban system is provided by the operators listed below. More information on the urban water system in the Melbourne region is available from the following websites:

• Melbourne Water
• City West Water
• South East Water
• Yarra Valley Water
• Western Water

The Statement of Water Assets and Water Liabilities for the urban water system (Table 10) shows that the volume of water in the urban water system changed little during the 2011–12 year in the Melbourne region.

Table 10  Statemet of Water Assets and Water Liabilities for the urban water system

Water assets	Volume at 30 June 2012 (ML)	Volume at 30 June 2011 (ML)
3 Urban water system
3.1 Urban water supply system	–	–
3.2 Wastewater system	25,202	24,219
3.3 Recycled water system	–	–
3.7 Urban claim on surface water	588,618	582,445
3.8 Urban claim on groundwater	0	0
Total urban water system assets	613,820	606,664
Opening net water assets	606,664	24,737
Change in net water assets	7,156	581,927
Closing net water assets	613,820	606,664

A volume was not presented in the water accounting statements for urban water supply systems. Water used to supply the urban system is stored in surface water storages and presented as 1.1 Storages.

The recycled water supply system could not be quantified accurately due to a lack of available data for the 2011–12 year. Given that this system is smaller than the wastewater supply system, the volume of water within the recycled water supply would have been relatively small and its exclusion from the water accounting statements is not considered to be material.

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the urban water system are provided in Table 11 and Table 12, respectively.

Table 11  Statement of Changes in Water Assets and Water Liabilities for the urban water system

Water asset increases	2011–12 volume (ML)	2010–11 volume (ML)
11 Urban water system increases
11.4 Wastewater collected	356,462	362,668
11.18 Increase of urban claim on surface water	425,527	937,686
11.19 Increase of urban claim on groundwater	412	413
11.21 Other urban water system increases	237	140
Total urban water system increases	782,638	1,300,907
Water asset decreases
19 Urban water system decreases
19.1 Evaporation from urban water system	18,622	4,141
19.2 Leakage to landscape	3,354	2,892
19.3 Leakage to groundwater	28,352	25,715
19.4 Delivery to urban water system users	353,309	352,622
19.5 Discharge from urban water system to surface water	12,161	15,390
19.6 Discharge from urban water system to irrigation scheme	3,089	3,457
19.7 Wastewater discharge outside of region	299,614	304,745
19.8 Other wastewater discharge	8	46
19.11 Transfer of water outside of region	146	53
19.17 Adjustment and forfeiture of urban claim on surface water	45,156	0
19.18 Adjustment and forfeiture of urban claim on groundwater	412	401
19.20 Other urban water system decreases	11,301	10,127
Total urban water system decreases	775,524	719,589
Balancing item – urban water system	(42)	(609)
Change in net water assets	7,156	581,927

Table 12  Statement of Water Flows

Water inflows	2011–12 volume (ML)	2010–11 volume (ML)
11 Urban water system inflows
11.4 Wastewater collected	356,462	362,668
11.12 Entitled diversion of allocated surface water to urban water system	374,198	355,241
11.13 Entitled extraction of allocated groundwater to urban water system	0	12
11.21 Other urban water system increases	237	140
Total urban water system inflows	730,897	718,061
Water outflows
19 Urban water system outflows
19.1 Evaporation from urban water system	18,622	4,141
19.2 Leakage to landscape	3,354	2,892
19.3 Leakage to groundwater	28,352	25,715
19.4 Delivery to urban water system users	353,309	362,668
19.5 Discharge from urban water system to surface water	12,161	15,390
19.6 Discharge from urban water system to irrigation scheme	3,089	3,457
19.7 Wastewater discharge outside of region	299,614	304,745
19.8 Other wastewater discharge	8	46
19.11 Transfer of water outside of region	146	53
19.20 Other urban water system decreases	11,301	10,127
Total urban water system outflows	729,956	719,188
Balancing item – urban water system	(42)	(609)
Opening water storage	24,219	24,737
Add/(Less): Change in water storage	983	(518)
Closing water storage	25,202	24,219

A schematic diagram representing all the inflows and outflows associated with the urban water system in the Melbourne region is provided in Figure 7. The inflow and outflow volumes for the urban water system during the 2011–12 year are given in Table 12. The numbers in brackets on the diagram refer to the line item numbers in Table 12.



Figure 7  Schematic diagram of water inflows and outflows for the urban water system within the Melbourne region during the 2011–12 year. Line item numbers are provided in brackets.

The urban system receives most of its water from diversion of surface water (11.12 Entitled diversion of allocated surface water to urban water system) and collection of wastewater (11.4 Wastewater collected). Information about the water access entitlements and water allocations under which surface water and groundwater are abstracted for the urban water system is given in the Water rights, entitlements, allocations and restrictions note.

Most of the treated wastewater is discharged into the sea (19.7 Wastewater discharge outside of region). The volume reported in the water accounting statements is the volume of wastewater discharged from the Melbourne region to Port Phillip Bay and Bass Strait.

The balancing item volume represents the difference between the measured opening and closing balances of the urban water system, after physical inflows and outflows have been applied. This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete urban water system store balance.

The balancing item is calculated according to Table 13.

Table 13  Balancing item for the urban water system for the 2011–12 year

	Account	Volume (ML)
	Opening balance (30 June 2011)	24,219
add	Total urban water system inflows (see Table 12)	730,897
less	Total urban water system outflows (see Table 12)	729,956
less	Closing balance (30 June 2012)	25,202
	Balancing item – urban water system	(42)

The calculation of the water balance on the urban water system yielded a negative balance item of 42 ML, representing a very marginal proportion of the total urban water system store volume and the total urban water system inflows during the 2011–12 year.