The chlorine used by the Hastings District Council to clear the town's water supply is useless, says a rural water expert.
More than 4700 people have been hit by gastric illness after Havelock North's water supply was contaminated with campylobacter. Interim tests have found it was most likely the bug came from ruminants such as cattle, sheep or deer.
Chlorine was put in the Hastings water supply - which now supplies Havelock North - to combat the bacterial outbreak, although authorities did warn it did not always kill parasites.
Lucy Waldron, an animal nutritionist who has researched freshwater for 20 years, said the chlorine used in New Zealand water was cheap, volatile, only effective for seven days and did not break down pathogen build-up in waterpipes.
Ms Waldron said she questioned the district council over using swimming pool chlorine, but was told it was part of a standard operating procedure that could not be changed.
She said pool-grade chlorine was not good enough.
"It only lasts a maximum of seven days before it's all driven off, so it's not a long lasting persistent chlorine for maintaining chlorine and driving off pathogens.
In a statement, the Hastings District Council said it was currently dosing water supplies with sodium hypochlorite at an initial dose rate of one part per million, and that would be adjusted until residual levels reached 0.7 parts per million (ppm).
"The Drinking Water Standards allows a residual chlorine level in the reticulation of a minimum 0.2 parts per million up to 1.5 ppm," it said.
"A public swimming pool typically has in the order of up to 10 times more chlorine than the water supply reticulation.
"Council continues to test chlorine levels at points right across the water supply reticulation system that is being chlorinated; in Flaxmere, Hastings, Bridge Pa and Havelock North."
But Ms Waldron, a director of consulting company LWT Animal Nutrition, said the chlorine that the councils were using did not work on biofilms.
"Biofilms are where you get an oily build-up around joints on water pipes and the bacteria secretes this biofilm and that gives them a safe place to reside and multiply. If you don't get decent biofilm penetration then, although the water is rushing past that has chlorine in it, you've still got the reservoir of bugs living in the pipes."
The council was aware there were better systems but had to operate under standard operating procedures, Ms Waldron said.
Many rural areas used copper sulphate in troughs to get rid of pathogens but care was needed with that method, she added.
"It gives the animals a massive copper overload, which reduces their ability to uptake the other minerals.
"There is research in Australia that shows copper sulphate in drinking water for animals leads to broken bones because it interferes with the uptake of other minerals needed for bone strength."
Ms Waldron said councils needed to catch up.
"Sometimes these standard operating procedures are not taking the latest research into account and they get stuck in one thing that has been OK'd, been registered, been cleared. It becomes almost a political situation whereby that is the way that we've always done it and that's the way we're going to do it, irrespective of whether there is new technology out there or not."
Contaminated water affects herds
Ms Waldron said Canadian research had shown milk production could drop because of contaminated water.
At the peak of the milking season, an average cow produced about 24 litres a day over two milkings.
"Milk yields can be reduced by 1.4 litres a day if an animal is exposed to high levels of contaminated water.
"The other problem for dairy cows is they require a lot of water for production and they tend not to want to drink contaminated water supplies."
The quality of water also affected animals' overall health.
"If they are in taking pathogens - whether that be bacteria, protozoa, toxic algae - whatever it is, then of course that is going to have a major impact on the animal's welfare and the health overall as well."