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• 3.0 Water Use

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• 3.1 Domestic; the "dom1" and "mun1" Categories
• 3.2 Stock Water
• 3.3 Industrial Water

This section summarises existing information on water allocation and water use in New Zealand. The aim is to estimate water use from water allocation figures in the domestic, stock and industrial categories. To do this, ratios of use to allocation across New Zealand are estimated using information from published data and unpublished surveys.

Actual use of water will vary over time. For example: water demand in summer is higher in summer than winter; water demand will rise and fall with population changes and changes in the efficiency of use; and long-term changes in industrial water use will vary with the mix of industries using water. It is appropriate to apply an estimate of the ratio because little data exists for New Zealand users.

3.1 Domestic; the "dom1" and "mun1" Categories

We estimate that an average of 46% of domestic water allocation is used by water suppliers for water suppliers outside Auckland. This estimate is taken from the mean of the use/allocation ratios (Table 13) for Ruapehu DC, Wanganui CC, Manawatu DC, Rangitikei DC, Palmerston North CC and Christchurch CC.

1. About 10% of Auckland's water comes from the Waikato and daily supply is "around 340,000 cubic metres" (Watercare website [external link]).
2. White and Sharp (2002) and unpublished data.
3. White et al., 2003.

The use/allocation ratio for Water Care Services's Waikato River consent (Table 13) is not considered typical of general use and so is not included in the estimation of average use. Water Care Services water use data is described in Appendix 3.

Not all water taken by municipal suppliers is used for domestic supply (Table 14). Therefore, two categories are defined that describe the use of domestic allocation (Appendix 2).

• dom1 - use of domestic allocation by domestic users
• mun1 - use of domestic allocation by industrial users

The dom1 class aims to estimate the water use by domestic users (U_dom1):

U_dom1 = 0.46 x 0.76 x A_dom

Estimated use of allocation by domestic users

0.76 - Estimated portion of allocation by domestic (i.e. non-industrial) users from mean of values in Table 14
A_dom - Allocation to domestic users

The mun1 class aims to estimate the use of domestic allocation by industrial users (Section 3.3).

Source: GNS surveys of water suppliers (unpublished). Christchurch City can account for 83% of its water use and of that an estimated 25% goes to commercial and industrial uses (Kerr et al., 2004) and the balance goes to other water uses.

3.2 Stock Water

Significant volumes of water are allocated for stock watering. However seepage from the water races, and to a lesser extent evaporation, account for substantial losses from these systems. Therefore use by stock is significantly lower than allocation (Table 15).

* "not more than"
1. Scott and Thorpe, 1986.

A recent study of the Paparua Scheme (Scott pers. comm.) gives 7% use by stock of the total water entering the stock race (Table 16). We therefore assume that the ratio of use to allocation is 7% for stock water.

3.3 Industrial Water

Water use by industry is commonly less than allocation (Table 17). Use of water by industry (U_ind) is estimated as:

U_ind = 0.4 x A_ind + U_mun1

0.4 - Estimated use of allocation by industrial users
A_ind - Allocation to industrial use
U_mun1 - Estimated use of mun1 allocation by industry

Use of allocation is assumed at 40% (Section 5.1.1) with the exception of the surface consents for Water Care Services. The use estimates in Table 17 give only a broad guide to use, leading to adoption of the 40% figure. Actual water use by Water Care Services of consents in the Auckland area (Appendix 3) are the figures in the allocation data; the Water Care Waikato consent uses 23% of allocation.

U_mun1 =0.46 x 0.24 x A_mun1

0.46 - Use of domestic allocation (Section 3.1)
0.24 - Fraction of domestic allocation for industry (Table 14)
A_mun1 - Sum of Lincoln Environmental (2000) mun and pws allocation.

The Lincoln Environmental water allocation data categories of mun (municipal) and pws (public water supplies) are combined into the mun1 use class. It is assumed that the water use of this water by industry is 0.46 times 0.24 i.e. 46% of the allocation is used and industrial users take 24%.

1. White et al., 2003.
2. GNS survey of water uses, unpublished.