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By Daniel Collins

I mentioned previously how much water we are allowed to use in NZ. The amount varies markedly from region to region, and is growing over time, with Canterbury and Otago accounting for well over half of the consumptive takes (excluding the Manapouri hydro scheme). But seeing as Kiwis seem to know less about our aquifers than our rivers, I’d like to turn now to the issue of where we can take our water from — rivers, lakes, aquifers or reservoirs (or storage lakes).

SWGWAllocation

About two thirds of the water NZers are allowed to take is from surface water — rivers and lakes. This is for all non-hydro schemes and other non-consumptive uses; the data come from a 2010 report from Aqualinc Research for MfE. About a third comes from groundwater. Five percent comes from reservoirs, which are largely fed by rivers.

Looking across New Zealand, we see that the relative importance of surface water, groundwater and reservoirs differs among regions. In Otago, surface waters are relied upon for 84% of the allocated water supplies; in Auckland, it’s 4%. In Hawke’s Bay, groundwater accounts for 74%; in Otago and Taranaki it’s 7%. And in Auckland, reservoirs account for 74%; in Waikato and Manawatu-Wanganui it’s zero.

So why do these proportions vary so much?

There are three key factors behind this: whether there’s enough water in the rivers; whether there are accessible and productive aquifers; and how important reliability of supply is to the water user.

Otago, for example, only has a smattering of significant aquifers, so they get most of their water from rivers. Hawke’s Bay, Southland and Tasman each have productive aquifer systems available. In the Auckland region, where over a third of NZ’s population needs to be provided with a reliable supply of drinking water, they turn to reservoirs and more recently to a reliable supply from the Waikato River via a tunnel. On the Canterbury plains, water from rivers and aquifers are both readily accessible and both highly used, though it is typically easier and cheaper to take water from rivers, even if the reliability of supply isn’t as high. You can see maps of NZ’s key aquifer systems here.

So we can see, yet again, that the physical environment has a huge effect on the availability and reliability of water supply in New Zealand. In posts to come, we’ll see what exactly this water is used for.