There's no doubting the most contentious issue in farming is water; not only the storage and harvesting of this most precious of commodities but, perhaps more importantly, the maintenance of its quality.

To that end, on The Country, we hosted the Great Water Quality Debate last week. In the red corner we had the controversial and outspoken water scientist, Dr. Mike Joy from Massey University, and in the blue corner it was Jacqueline Rowarth, a Professor of Agribusiness from Waikato University.

In conjunction with the on-air radio debate we ran a poll on our website asking, "Is intensive dairy farming degrading our waterways?" At the time of writing, from 650 respondents, 74% said yes, 22% no and 4% did not know.

Although it was somewhat of a leading question, it did confirm the real bias many New Zealanders have against dairy farming.

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Follows is what Mike Joy had to say:

# The Havelock water crisis has highlighted the degradation of water in New Zealand from intensive agriculture. Ground waters in agricultural and urban catchments are being degraded with increasing nitrate levels found at 39 percent of monitored sites nationally. At a further 21 percent of sites, groundwater is contaminated, with pathogen at levels exceeding human drinking standards. That was in 2007, so it's very likely to be worse now.

# Surface waters in lowland agricultural areas such as Southland, Canterbury, Manawatu, Hawkes Bay, Taranaki and Waikato exceed guideline levels for nitrogen, phosphorus and pathogens. We know groundwater is fed by surface waters.

# We may never know the exact cause of the campylobacter outbreak but we do know from DNA the source is likely a ruminant.

# There are large feed pads on the banks of the Tukituki River upstream from the aquifers. There was a flood 10 days before the peak of the outbreak, and when the river is in flood it flows at more than 10km/hr thus the whole catchment has the potential to be the cause. The most numerous ruminant in the catchment is cattle thus the probability is high that this will be the source, but hopefully the inquiry will have some kind of answer.

Jacqueline Rowarth countered with these arguments:

# There is considerable confusion out there. Drinking water in municipal jurisdictions in developed countries is mostly treated (chlorine, ozone, UV) to ensure microorganisms don't infect drinkers. New Zealand has relied on the depth of aquifers but top-of-bore contamination has occurred recently in places such as Darfield, where bore contamination from sheep is thought to be the cause. Infection from this source is prevented as long as treatment occurs before water goes into domestic pipes.

# New Zealand has relatively high rates of campylobacter. But most infections come from incorrectly prepared or cooked food.

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# As for the river issue, dairy animals are being fenced off to ensure no direct contamination. Drystock farms are working on fencing, sediment traps etc. Now they know the problem they are working on changes, just as the dairy industry has.

# Sediment remains a problem. Slips and slumps are natural, as is bank erosion in flood. The Parliamentary Commissioner for the Environment has pointed out that construction, forestry and cultivation all have an effect in increasing potential sediment loss.

# E coli increases in rivers in flood and when water is warm and static. But most rivers are in the range that Europe and Australia call good quality for swimming.

I thought I'd leave the final say to another of my radio guests last week, Dr Graeme Coles, the technical director of Knewe Bio-Systems. In response to Mike Joy's claim that we need to rid the food chain of animals by 2050, Coles said dairy produce is an efficient and cost-effective food source.

He cited the example of the number of people you can feed from one hectare - dairy can feed nearly four-times as many people as the best plant-based foods, even though he reckoned dairying needed to be more sustainable.

When I asked him if animals are, as many claim, inefficient converters of water to food, Coles countered by saying animals recycle water and it's used as many as four to five times on the journey from the well to the sea. Contrast that to a cropping scenario, he said, where the water is used once then evaporates into the atmosphere.

I like Mike Joy but he thinks I set him up for a fall on my radio show. That's not true. I've given him a fair hearing. But when you want animals out of the food chain, in a country that pays its way in the world off the back of dairy and meat production, you are truly swimming in murky waters against the tide of farming opinion.