8.0 Future Trends in Water Use

New Zealand Water Bodies of National Importance for Domestic Use and Industrial Use

P A White, B M H Sharp and R R Reeves, Institute of Geological & Nuclear Sciences

[ Last Updated 17 January 2006 ]

8.1 Future Domestic Demand
8.2 Industry

Future changes in water use are estimated applying Statistics New Zealand [New Zealand Government link] projections of population change in the period 2001 to 2021 to the water use from 1999 consent allocations. Statistics New Zealand medium-rate figures (Table 27) predict that the Auckland region will grow by 434,800 people, or 36% to 2021. Population growth is predicted in nine regions; population decline is predicted in six regions. These population changes may impact on water use for domestic purposes.

8.1 Future Domestic Demand

Estimates of future water use are made using:

E₂₀₂₁ = E₁₉₉₉ x G

E₂₀₂₁ = Estimated water use in 2021
E₁₉₉₉ = Estimate water use in 1999
G = Regional population growth (Table 27)

Population growth figures are for 2001 to 2021. It is assumed that these growth projections are applicable for 1999 (the date of consent data) to the 2021 period.

This calculation does not consider intra-regional population change (Section 8.1.1) nor changes in the efficiency of water use (Section 8.1.2). Predictions of future domestic water use are made for surface water catchments and groundwater aquifers.

8.1.1 Intra-Regional Population Change

Populations in districts within regions are expected to change in the next 20 years. Statistics New Zealand, on their website, predict population changes by district council and by city council. An example of intra-regional population change is provided by the population of Canterbury. The Canterbury region is predicted to grow in population with most of the population increase in Christchurch City, Waimakariri District, and Selwyn District (Table 28). Population declines are predicted for Timaru, Ashburton, Waitaki, and Waimate. Therefore the regional

Table 27: Projected Population of Regional Councils - Medium-Rate Projections, 2001(Base)-2021
Regional Council	Projected Population at 30 June		Change 2001-2021
Regional Council	2001⁽²⁾	2021	Number	Percent
Northland Region	144,400	157,900	13,500	9
Auckland Region	1,216,900	1,651,700	434,800	36
Waikato Region	369,800	409,700	39,900	11
Bay of Plenty Region	246,900	307,700	60,800	25
Gisborne Region	45,500	42,600	-3,000	-6
Hawke's Bay Region	147,300	145,500	-1,900	-1
Taranaki Region	105,700	95,400	-10,400	-10
Manawatu-Wanganui Region	227,500	225,500	-2,000	-1
Wellington Region	440,200	469,200	29,000	7
Tasman Region	42,400	50,400	8,000	19
Nelson Region	42,900	50,400	7,500	17
Marlborough Region	40,700	45,700	5,000	12
West Coast Region	31,100	27,400	-3,700	-12
Canterbury Region	496,700	550,200	53,500	11
Otago Region	188,300	196,500	8,200	4
Southland Region	93,300	79,400	-13,900	-15

Source: Statistics New Zealand website, February 2004

1) There are three alternative projection series incorporating different fertility, mortality and migration assumptions for each area.
2) These projections have as a base the estimated resident population of each area at 30 June 2001.

Notes:
All derived figures have been calculated using data of greater precision than published. Owing to rounding, individual figures may not sum to give the stated totals.
Owing to rounding, individual figures may not sum to give the stated totals.

Table 28: Projected Resident Population of Canterbury Territorial Authority Areas 1996 (Base)-2021 (May 2000 Release) Sorted by Estimated Population in 2021
Area	Growth Projection	Year at 30 June						Change 1996-2021
Area	Growth Projection	1996 (1)	2001	2006	2011	2016	2021	Number	Percent
Christchurch City	Medium	316,500	327,000	336,500	344,500	352,000	358,500	42,000	13
Waimakariri District	Medium	32,900	36,700	39,800	42,800	45,500	48,200	15,300	47
Selwyn District	Medium	25,400	29,000	32,100	35,100	38,200	41,200	15,800	62
Timaru District	Medium	43,300	41,600	40,900	40,000	38,900	37,800	-5,500	-13
Ashburton District	Medium	25,600	25,400	25,300	24,900	24,400	23,800	-1,800	-7
Waitaki District	Medium	21,900	20,500	20,000	19,400	18,700	18,000	-4,000	-18
Hurunui District	Medium	9,600	9,900	10,100	10,300	10,500	10,700	1,100	11
Banks Peninsula District	Medium	7,700	8,100	8,400	8,600	8,800	9,000	1,300	17
Waimate District	Medium	7,800	7,400	7,100	6,800	6,600	6,300	-1,500	-19
Mackenzie District	Medium	4,200	4,300	4,400	4,500	4,500	4,500	300	8
Total		494,900	509,900	524,600	536,900	548,100	558,000

(1) These projections have as a base the estimated resident population at 30 June 1996.

Note: Owing to rounding, individual figures may not always sum to the stated totals.

8.1.2 Efficiency of Water Use

Water scarcity can sometimes lead to efficiency in water use, and Tauranga is an example. Tauranga District Council installed water meters in a programme that started in 2000 and was completed in 2003. Water meters were installed primarily to manage demand and increase efficiency. The efficiency of water use has apparently increased since the council started installing water meters. Water production was 400-500L/person/day between 1995/1996 and 1998/1999. Water production by 2002/2003 declined to around 325L/person/day (Spier pers. comm.).

8.1.3 Future Water Use and Allocation

Domestic water use is currently an estimated 46% of allocation (Section 5.1.1). Future growth may therefore be accommodated within existing allocation. For example, Rotorua City Council has found that current water allocation in the eastern, central and Ngongotaha supply areas are sufficient to cope with projected population growth to 2027 (Manzano pers. comm.).

8.1.4 Surface Water Catchments

Allocations in all regions except Auckland for domestic use in the Lincoln Ventures (2000) allocation categories of cws, dom, dom/stock, mun, nulltype, pws and rws are multiplied by regional growth estimates (Table 27) and by estimated use of 46% to project future use.

Future use in Auckland is estimated by a different method because of the assumption that future Auckland water supplies will come from the Waikato River, i.e.:

water use in 2021 from the Hunua, Nihotupu, Huia and Waitakere reservoirs will be the same as 1999
total Auckland water use in 1991, of approximately 2.1 million m³/week (Appendix 3) will grow by 36% to approximately 2.9 million m³/week in 2021 because population growth is estimated as 36% (Table 27)
the Waikato River will supply all the growth in future use
the growth in use to 2021 is estimated at around 760,000m³/week which means that Auckland's take from the Waikato River in 2021 is an estimated 794,000m³/week

Estimated use in 2021 will be largest the Waikato River, Wairoa (Auckland) and Clutha catchments (Table 29). Water use for domestic supply is projected to decline in some catchments with greatest declines in the Oreti catchment (Southland) and Taranaki catchments.

8.1.5 Groundwater Aquifers

Future use of groundwater aquifers is estimated using allocations in all regions for domestic water use in Lincoln Environmental's (2000) cws, dom, dom/stock, mun, nulltype, pws and rws water allocation classes multiplied by regional growth estimates (Table 27) and multiplied by estimated use.

Use of groundwater is estimated as largest in the Christchurch-West Melton, Heretaunga Plains, and Hutt aquifers (Table 30).

Groundwater use is predicted to decline for a number of aquifers because the populations of some regions are predicted to decline to 2021 e.g.:

coastal aquifers, Southland, decline of 7878m³/week
Heretaunga Plains, Hawkes Bay, decline of 5063m³/week
Wairau groundwater (Southland), decline of 4154m³/week

8.2 Industry

Specific projections of water use by industry are not made as 20-year-ahead predictions of the type and location of industry are not known to the writers. However, some hint of the future requirements of industry are given by the trends in domestic water use (Table 29 and Table 30) as industry commonly takes water from municipal supplies.

Table 29: Projected Water Use of Surface Water Catchments by Domestic Users in 2021 - Catchments with the 20-Largest Estimated Uses
Rank	Catchment number	Catchment name	Region	Estimated use 2021 m³/week
1	2	Waikato	EW+ARC	2231360
2	275	Wairoa	ARC	853705
3	1	Clutha	ORC	545505
4	147	Hutt	WRC	344885
5	726	Waipapa	NRC	309312
6	860	Huia	ARC	298376
7	902	Nihotupu	ARC	254218
8	72	Kaituna	EBOP	243249
9	30	Rakaia	CRC	237348
10	414	Waimapu	EBOP	219576
11	9	Taieri	ORC	215231
12	435	Kerikeri	NRC	207527
13	45	Waihou	EW	195742
14	377	Waiwhakaiho	TRC	175271
15	19	Waiora	NRC	173521
16	22	Ruamahanga	WRC	172340
17	494	Kopurerua	EBOP	150024
18	20	Oreti	SRC	147798
19	3	Waitaki	CRC	136843
20	381	Wainuiomata	WRC	94059

Table 30: Projected Water Demand of Groundwater Aquifers by Domestic Users in 2021 - Aquifers with the 20-Largest Estimated Uses
Rank	GNS aquifer name	Region	Estimated use in 2021m³/week
1	Christchurch-West Melton	CRC	1722895
2	Heretaunga Plains	HBRC	501301
3	Hutt	WRC	473994
4	Auckland volcanics	ARC	264579
5	Ashley Downs	CRC	251885
6	Central Plains	CRC	213496
7	Rangitata-Levels plains	CRC	174696
8	Central Otago	ORC	164459
9	Manawatu	HMW	155918
10	Mamaku Plateau	EBOP	149859
11	Upper Wairau Valley	MDC	144660
12	Lower Taieri Plain - East and West	ORC	143962
13	Rakaia-Ashburton plains	CRC	127600
14	Coromandel volcanic	EW	116694
15	Upper Confined	TDC	101709
16	Whakamuru Ignimbrites	EW	86360
17	Wanganui	HMW	84722
18	Rangitaiki Plains (assumes shallow system)	EBOP	74567
19	Raumati-Paekakariki	WRC	59748
20	Matahina Ignimbrite	EBOP	52784

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Printed: 25/11/2009