Power Play - New Zealand has long relied on its clean green image, but could this become hard for tourists to swallow after thousands of people fell ill from drinking contaminated water?

Photo: Wikicommons

Tourism New Zealand has doggedly persevered with its 100 Percent Pure campaign to promote New Zealand overseas, even after Prime Minister John Key was raked over the coals about it on BBC's Hardtalk programme five-years ago.

During that interview Mr Key admitted the intensification of dairying in New Zealand had had "some impact" on the country's river quality.

According to Statistics New Zealand, between 1990 and 2012 the estimated amount of nitrogen that leached into soil from agriculture increased by 29 percent.

Nitrogen and phosphorus, which also increased in prevalence over that time, are considered nutrients in waterways.

This means that while they are natural parts of an aquatic ecosystem, if they reach high levels, algae in the water grows at an exponential rate and essentially suffocates the water by taking up all the available oxygen.

So that is all bad news for the health of the river - but what about the health of people?

Aside from heavy metals in water, human health is also affected by another contaminant - Escherichia coli or E coli, which comes primarily from faecal contamination, or more plainly, poo.

This was the contaminant found in Havelock North's water, with 5200 people struck down by gastrointestinal illness in the biggest water-borne outbreak in the country's history.

Opposition parties have been using that event to attack the government, saying it is allowing the quality of the country's water to rapidly deteriorate.

But this has not just been happening under the current government's watch - New Zealand's water quality has long been heading in the wrong direction.

The problem is current and historical land-use practices, as has been well documented.

Is this good enough? Cattle get free access to Canterbury's beautiful Lake Taylor beside DoC's public camping ground pic.twitter.com/UbszCVUH09 — Fish and Game NZ (@FishandGameNZ) January 19, 2016

Pictures often shared by environmentalists of cows standing in rivers are dramatic, but that is not really the true source of the problem.

There are two main ways water is polluted: from a point or a diffuse source.

A point source of pollution comes from an identifiable single source, for example a pipe into a river.

A diffuse source is where the pollution has no specific point of discharge - and this is the main cause of New Zealand's water quality problems.

Animal faeces, urine and fertiliser spread on land leach contaminants into the soil, which then make their way into the groundwater, feeding into aquifers and streams.

Controlling diffuse source pollution is a hugely difficult task and for a country with an economy reliant on primary production it is a monumental problem, as New Zealand's other big money spinner, tourism, relies heavily on having clear, clean waterways.

Watch any Tourism New Zealand campaign video and you'll see people frolicking in rivers, paddling across beautiful lakes or admiring gushing waterfalls.

In 2014 the government set the national bottom line for water quality as "suitable for wading or boating".

Currently 98 percent of waterways meet that target, so the government can safely claim almost all of the country's waterways meet its water quality standard.

But is that a real measure of the health of the country's water?

Environmental groups argue the measure is ridiculous, and creates no motivation to improve water quality.

They, and the Green Party, want the bottom line for water quality to be set as "suitable for swimming". Currrently more than 60 percent of rivers fail the health standard for swimming.

However, Minister for the Environment Nick Smith said it was impossible to make all the country's lakes and lagoons swimmable because of all the birds pooping in the water.

That may be so, but what would the harm be in setting a target that at least inspires some action towards tackling the ballooning problem of water degradation?

Yes it would mean a rather unsavoury statistic, but with thousands of people getting sick from drinking a glass of water from their tap, at least it would be a more honest assessment of New Zealand's water quality.

It might, of course, also mean having to change the country's tourism slogan to 40 Percent Pure.