Farmers irrigating just north of Christchurch are using the latest technology to ensure not a drop in wasted.
The water is drawn from the ancient, slow moving aquifer which also supplies domestic drinking water to the city's residents.
In the first project of its type in New Zealand, the latest in digital technology has been rolled out to Waimakariri Irrigation's farmer-shareholders, taking the guesswork out of irrigating.
The Waimakariri Irrigation scheme delivers river water to 200 shareholders and irrigates 23,000 hectares between the Waimakariri and Ashley rivers.
While the scheme was unusual in that almost half its shareholders were smaller and lifestyle blockholders, it was the 108 farming operations, which make up 90 per cent of its land area and take 95 per cent of its water, that were under increasing scrutiny to account for their watering decisions.
Environment Canterbury's Waimakariri water zone committee chairman David Ashby said the area had serious challenges to address in terms of low flows, groundwater depletion, and water quality.
A small number of dairy farms concentrated in the Eyre area (on the north bank of the Waimakariri River) had the technology implemented first.
"With 80 per cent of dairy development occurring in this area, which feeds into Silverstream, we have an issue with nitrate levels."
The Silver Stream winds its way through the Silverstream Reserve, a 52ha native bush reserve near the town of Clarkville. It was renowned for its clear, spring-fed waters, trout fishing and seasonal salmon and significance to local Maori for mahinga kai – the gathering of food.
Ashby was confident that technology would improve water quality. "Let's watch the next two to three years."
Waimakariri Irrigation chief executive Brent Walton said farmers were sent automated daily science recommendations to their mobile phone.
"A year on we have seen significant behavioural change in how farmers irrigate. Farmers have adopted a more scientific, information-based approach, rather than just turning on the irrigator because the neighbour has."
Waimakariri Irrigation's catchment area was also hydraulically-linked to a Belfast aquifer, used for domestic water and the controversial Chinese-owned Cloud Ocean Water bottling plant.
"Research has identified that some deep aquifer water under the Eyre zone moves under the Waimakariri River to the northern city aquifers around Belfast. This movement is long-term, over 50 to 100 years, but we want to take action to do the right thing now," Walton said.
By ensuring that irrigation is justified, auditable and recorded, "we can significantly reduce the nitrate leaching that is caused by irrigation and demonstrate that is the case".
Larundel dairy farm contract milker Ben McKerchar, with Regen chief executive Bridgit Hawkins. The farm's owners have spent hundreds of thousands of dollars on improved irrigation technology and effluent disposal.
Water, whether applied by rainfall or irrigators was measured, with Waimakariri Irrigation investing in about 20 weather stations which showed that rainfall varied significantly, even within its catchment area.
"If is forecast to rain today, then you stop irrigating yesterday. There is no point irrigating right up to the rain event as the ground is already wet. If you put rain on top of that, that's when leaching occurs."
All data was managed by agricultural software provider Regen and provides each farmer an individual five-day rolling irrigation recommendation via a mobile app, as well as recording what they do, for compliance.
Waimakariri Irrigation's catchment area is hydraulically-linked to a Belfast aquifer, used for domestic water and the Cloud Ocean Water bottling plant.
Larundel dairy farm contract milker Ben McKerchar said the technology complemented an on-farm investment, worth hundreds of thousands of dollars, in more water efficient centre pivot irrigators.
"It just pulls all the information into one app on my phone. In spring, when 11mm of southerly rain was predicted, we turned off the irrigators the day before and the recommendation was no irrigation for at least five days."
This meant soil moisture always stayed within the ideal range for pasture growth, while avoiding the risk of nutrient leaching.
A wet spring meant Larundel did not irrigate in November or December which had never happened before. "We started watering again on January 2."