I'm heartened by Labour's proposal to charge a royalty for water use and earmark that money for cleaning up our rivers.

Not because I think this is the best policy response, it just shows to me that a threshold of concern has been reached. A majority of people in this country want something done about our polluted waterways, and quickly.

Labour would never have announced the policy unless it thought it would go down well with a good many voters. It is too poll driven to go out on a limb. Which is one good thing about political gradualism, if enough people want it politicians can eventually get around to doing something about it, or at least the appearance of doing something.

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There's been condemnation of course. If you're a farmer, a water bottler, you don't want the extra cost.

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And maybe, if Labour is elected, introducing the royalty will be the straw that breaks the cow's back for some indebted dairy farmers. Though I'd suggest rising interest rates and the next spike in oil prices will do this first.

But if we take a longer view than electoral cycles, the evidence is pretty clear that intensive dairy farming for export - by far the main factor behind our polluted rivers - has no future in New Zealand.

Global food production is incredibly competitive. The average food buyer has many options at the supermarket, with a significant trend emerging towards plant-based products. Think vege burger washed down with a soy milk smoothie.

Apart from the environmental and health factors that motivate many people, plant-based proteins are going to claim a bigger share of the world market because plant crops require less land and water than your average one tonne cow.

Meat and dairy substitutes derived from plant products will impact the price and quantity of milk powder and other dairy products sold.

But the more significant trend is the producing of food closer to where it's consumed. The environmentally conscious are demanding it. The increasing cost of transport, as the oil price rises, will dictate it.

To be seen to be doing something about global warming, governments worldwide are going to have to put in place taxes and restrictions on the use of fossil fuels. This will be hard fought politically, but the trend won't go away.

A combination of taxes and oil shortages will contract world trade for basic commodities. Planes and freighters don't run on renewables, and the laws of physics mean they never will.

So the way we feed ourselves will simply have to change. People will grow a larger portion of their own food in their backyards, more food will be grown closer to cities, even within cities, as new technologies and attitudes allow.

If I was a dairy farmer I'd be tempted to get out now before the rush. Or convert land to something more sustainable and supply a range of food products to the local market.

Dairy farming in New Zealand will eventually retreat to the most suitable climatic regions and supply a local population.

There won't be a surplus to sustain Fonterra board members, corporate shareholders or big banks. Massive dairy herds in Canterbury will be thing of the past.

New Zealand's waterways will recover. We'll be swimming in our rivers again and the world will be a very different place.