However, before that happens the 35 applicants - all upstream of the Waitaki dam and as far west as above Lakes Tekapo and Pukaki - who want the water will have to get resource consents from Environment Canterbury (ECan).
Those applications, some dating back more than six years, will come under the scrutiny of a three-commissioner panel appointed by ECan from September 21 at hearings expected to last up to 10 weeks, the bulk in Christchurch, with some in Twizel.
The panel is chaired by former Environment Court judge Prof Peter Skelton.
Applicants and opponents, supported by legal counsel, have indicated about 80 expert witnesses may be called for the hearings.
A group of 19 applicants have combined to form the Upper Waitaki Applicants' Group to present their case.
Meridian Energy Ltd, who has a big stake in water use in the catchment because of its Waitaki hydro electricity system, is also closely involved.
The two big issues applicants face are the effect land use intensification from irrigation will have on pristine lakes, rivers and stream in the upper Waitaki catchment and the effect on the landscape.
The landscape effects are likely to be controversial.
Already environmental groups - such as Royal Forest and Bird - and the Department of Conservation and Canterbury Aoraki Conservation Board are voicing opposition to turning large areas of the region into green pastures.
The effect irrigation has on the landscape is already graphically evident between Omarama and Twizel where the Benmore irrigation scheme has turned what was tussock land, infested with hieracium and patches of scrub, into pasture or arable areas, including a dairy farm.
Prof Skelton has already indicated that landscape issues may be relevant in relation to the water applications, although he has yet to make a final decision, depending on legal arguments.
Irrigation would cut across proposals for a dryland park in the region as well as having a major effect on threatened flora and fauna habitat, critics say.
Te Runanga of Ngai Tahu and its Moeraki, Waihao and Arowhenua runanga are also involved, along with the New Zealand and Central South Island Fish and Game Councils.
On the other side are farmers and community members, who argue irrigation will provide a lifeline for properties under threat, stop wind-blown soil erosion and offset the loss of land through tenure review.
It will boost the region's economy and provide more jobs, they say.
The water quality issue is another many applicants will face.
Many are funding a study, which has already produced a draft report, from Mackenzie Water Research Ltd, on the cumulative effects of all the irrigation proposals on water quality and possible mitigation.
That report, which will be the first to be considered by the panel when it starts sitting is likely to take five days, including evidence from consultants who have prepared it.
The applications will have to be considered in conjunction with the Waitaki catchment water allocation regional plan, which sets minimum flows for streams and rivers, lake levels, efficiency of water use and allocates volumes of water for various uses.
In the catchment above the Waitaki dam, the plan set an annual allocation of 275 million cubic metres of water a year for agricultural and horticultural use.
The applications to be considered propose using 146 million cubic metres of water a year.
The applications will be split into sub-catchment groupings and heard in an order which reflects the way the allocation plan has been written.
After the water quality report, applications in the headwaters will lead off the hearings with the panel working its way down to the Waitaki dam.
Wanting water
> 126 applications from 35 applicants above the Waitaki dam.
> Most of the applications are to renew or for new irrigation.
> More than 27,000ha of irrigation.
> Water takes range from upstream of Lakes Pukaki and Tekapo down to the Waitaki dam.
> Hearings may last up to 10 non-sequential weeks starting September 21 and concluding December 18.
> Bulk of hearings in Christchurch, some in Twizel.
> Hearings panel commissioners, former Environment Court judge Prof Peter Skelton, chairman, (Christchurch), environmental consultant Mike Bowden (Kaiapoi) and a third to be appointed.
