Irrigation is increasing on Rangitikei's coastal sand country and Horizons Regional Council has measures in place to pull it back if there are adverse effects.
Over the last five years more and deeper bores have been sunk, Horizons science and innovation manager Abby Matthews said. Land use is changing from a mix of sheep and beef and forestry to dairy, irrigated sheep and beef, cropping and some horticulture.
Some irrigated dairy farms use 10,000 cubic metres of water a day - the same amount as the whole town of Marton.
The newest bores are mostly 200m to 250m deep and can be up to 400m deep, sunk to get guaranteed water after levels in 50m-100m deep bores declined between 2007 and 2015.
If "trigger" points are reached, the owners of the new bores will have to cease or limit their water takes in the following season. That gives them "some level of risk" to their farming business, Ms Matthews said.
"If the decline continues the person can be cut off or drop back next season."
The new measures have been in place for about 18 months, and no trigger points have been reached so far.
The owners of new and deeper bores have also had to install extra monitoring wells, as part of their resource consents. The OB Group, with a new dairy farm near Koitiata, has even installed a salt water intrusion monitoring station, the seventh along the Horizons Region coastline.
The intrusion of salt water from the sea is possible if freshwater underground is depleted enough.
Under resource management law the council can't unnecessarily restrict water takes, but it does have to make sure they are sustainable. New applications for water take have slowed, with four since January 2015.
"I'm confident there's enough ability for us in that framework to limit things if we start to notice [the takes] having an impact," Ms Matthews said.
It's hard to say exactly how much underground water can be taken in coastal Rangitikei without affecting the amounts available for other people and for replenishing aquifers and coastal lakes and wetlands.
Ms Matthews said current takes are perhaps 20 to 30 per cent of what is possible. Only 10 per cent of what is taken is used for public water supply.
Water levels in 50m-100m bores declined from 2007 to 2015, but they have stabilised now, perhaps because of the last very wet winter and spring.
Under climate change this area is expected to have drier summers, more wind and wetter winters and springs.