Several Auckland suburbs were issued a boil water notice after E coli traces were found. Photo / 123rf
By Nik Dirga of RNZ
Explainer: What does it mean when a boil water notice is issued because of possible E coli contamination? Here’s what you need to know.
Several Auckland suburbs were put under a boil water alert on Monday night after routine water sample testing showed traces of E coli.
The notice was for about 7500 households in parts of Hillsborough, Mt Roskill, Royal Oak and Three Kings.
That doesn’t necessarily mean there’s a major E coli outbreak.
“From time to time, a single E coli result can occur for reasons that don’t reflect a problem in the network itself,” Watercare chief operations officer Mark Bourne said.
“For example, it could be caused by contamination at the sample tap, or environmental factors like wind or rain during sampling.”
Watercare is continuing to monitor the situation and has said it will update the public.
E coli scares in water have happened several times before.
It’s short for Escherichia coli and basically, it’s a kind of bacteria.
We all actually carry it around in our lower intestines, and that’s where it should stay in healthy people as part of your digestive system.
But if certain strains of E coli are consumed by drinking contaminated water, eating contaminated foods such as undercooked meats or raw milk or contact with animal faeces, then you’ve got a problem.
Most types of E coli are harmless, Health NZ says, but some can cause diarrhoea or gastroenteritis.
That’s not pleasant for anyone, of course, but in some people – young children, older people or those with compromised immune systems – it can be much more dangerous.
“We test for it as part of our regular monitoring programme, which sees us sample all of Auckland’s water supply distribution zones at least once a day,” Bourne said.
A strain of E coli known as Shiga toxin-producing can cause severe disease – symptoms include abdominal cramps and diarrhoea that may in some cases progress to bloody diarrhoea, the World Health Organisation says.
Last year, a Christchurch man said his daughter got violently sick and was hospitalised for 10 days after drinking Shiga E coli contaminated water at a north Canterbury campground.
“She was very sick, she had diarrhoea, stomach cramps, she was very lethargic, she was hooked up to an IV line and fed intravenously – she wasn’t well,” the father told RNZ.
“Most patients recover within 10 days, but in a small proportion of patients (particularly young children and the elderly), the infection may lead to a life-threatening disease, such as haemolytic uraemic syndrome,” WHO writes.
There’s no specific treatment for E coli, other than rest and drinking plenty of fluids to prevent dehydration.
Health NZ’s website also offers more tips for dealing with gastroenteritis.
The best way to avoid getting E coli is to wash your hands regularly and follow food and water safety advice, Health NZ says.
If your symptoms haven’t gone away in seven days or you have bloody diarrhoea or a fever, you should see a healthcare provider.
For children, watch to see if they’re not drinking, not passing much urine, if they have a dry mouth or sunken eyes or seem drowsy. If so, they need to see a doctor as soon as possible.
Regular water samples are conducted by authorities to check for quality and safety.
Bourne told Morning Report that all other testing in the area showed normal results, and the boil water decision was made to protect public health while investigations continued.
“Typically we’re taking about 40 samples throughout the networked area of Auckland each day. Those samples are then analysed for a range of parameters. One of those parameters is E coli.”
Bourne said Watercare was investigating how E coli could have possibly entered the water supply.
“Part of our rapid response yesterday evening and overnight was we’ve undertaken investigations of the local reservoir that supplies the area, and we’ve walked all of the upper reaches of the water supply pipelines.”
“Our water treatment plants are also continuously monitored for water quality parameters to make sure we meet the Drinking Water Quality Assurance Rules set by the Water Services Authority Taumata Arowai and provide safe and reliable drinking water to our customers.”
“When it comes to these rare positive results, we have taken guidance from Taumata Arowai and are working with them to take a precautionary approach,” Bourne said. “That means if we get a positive result, we may issue a boil water notice while we carry out further testing.”
Boiling water in an electric kettle is sufficient to kill bacteria and other organisms, Watercare notes on its website. The water only needs to be boiled once, then it can be cooled before use.
“All we need to do is literally boil [water] in an electric jug, and then if you want to drink it cool, let it cool down,” Bourne said.
“These are rare events – on average we might see around three isolated detections a year – and in those cases, all other test results have been normal, and follow-up testing confirms the water is safe,” Bourne said.
“We have robust processes in place to maintain our network’s integrity and minimise the chance of contamination.”
There have been other incidents around Aotearoa.
A study in 2023 found that about half the groundwater wells across the country monitored long-term were contaminated with E coli.
And last year, the Water Services Authority said the risk of E coli contamination in many school water supplies is extremely high.
The authority’s Drinking Water Regulation Report for 2024 said 71 schools reported at least one instance of faecal contamination of their drinking water last year.
Bourne said Watercare’s approach “puts public health first and is increasingly being adopted across New Zealand”.
“Once we are confident that all results are back within drinking water standards, the notice is lifted.”