Groundwater levels prior to the start of this irrigation season in mid-Canterbury (1 September 2025) were among the highest observed over the past 20 years, based on various ECan monitoring bores of depths typically used for irrigation. This marks an impressive rebound from the low winter and summer groundwater levels of 2024.

These current high-water levels are thanks to a significant amount of aquifer recharge that has occurred over the previous autumn and early winter, including the effect of the rainfall event that caused widespread flooding in the Selwyn District in early May. Aquifer recharge is the process by which rainfall on the land surface and river seepage replenish groundwater stored in the underlying aquifers. Across the Canterbury Plains, recharge is largely driven by rainfall and alpine river flows from preceding seasons. Monthly rainfall totals during the 2024–25 summer and autumn were well above average, providing a major boost to groundwater storage going into this irrigation season. The higher summer rainfall meant that abstraction was lower, and the winter recovery of groundwater levels started from a higher baseline.

Adequate aquifer recharge is essential to balance groundwater abstraction and maintain reliable water supplies, and water allocation rules are designed to ensure that this balance is maintained. While groundwater levels are expected to fluctuate between years, a decline year-on-year can reduce bore yields and affect ability to access consented abstraction volumes, as well as having effects on groundwater-dependent ecosystems such as lowland streams. Water use within sustainable limits helps ensure that groundwater remains a dependable resource for the ecosystems, communities and businesses that depend on it in future years.

In Canterbury, some resource consents to take groundwater are subject to adaptive management conditions: an assessment of the groundwater levels before the irrigation season which influences how much water can be taken under these consents over the summer. If groundwater levels in designated monitoring bores are below specified thresholds in spring, a consent-holder may have their allocation reduced over the following irrigation season. While surface water users are used to managing around restrictions when river flows are low, it is a relatively uncommon situation for groundwater users to be restricted in this way. The restrictions can be severe: if groundwater levels are very low, there is a risk that no allocation at all will be available. Based on current monitoring, most adaptive management groundwater consents are unlikely to face restrictions to their water supplies this irrigation season — welcome news for groundwater users, as those farming will know well that any reduction in water allocation for a season may have a substantial impact on farm management and productivity.