E. coli has been found in the drinking water for two Waiheke schools.

Waiheke High School principal Jude Young said the school, which uses bore water, discovered a "high" E. coli count in its water on Wednesday.

The neighbouring Te Huruhi Primary School tested positive for E. coli two weeks ago.

The Education Ministry was alerted to the contamination last night and is looking into the incident. The cause of the contamination is unknown.

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Young told the Herald parents were alerted by email on Wednesday. None of the high school's pupils had become sick but she would not comment on the situation at the neighbouring primary.

"We needed to replace some filter systems, which has happened today," she said.

The high school must wait until it receives three clear tests back before it can start using the water again, which may take about a week.

Until then, the school will be shipping in clean drinking water on a daily basis.

E. coli-related illness can cause stomach pains, mild to severe diarrhoea, vomiting and fever.

Symptoms can be severe for children, elderly people, or those with weaker immune systems.

Young said the high school's water testing was clear when Te Huruhi Primary School's water tested positive a fortnight ago.

She would not comment on the primary school's process after the readings came back. The primary school could not be reached for comment last night.

The high school has a roll of 517 students while the primary school has 389.

The Ministry of Health said the matter would be handled by the Auckland Regional Public Health Service, which did not respond to Herald inquiries last night.

The Ministry of Education only learned of the contamination last night and a spokesman said it was being looked into.

The discoveries come not long after E. coli was found in Lower Hutt water.

Chlorine has been added to Lower Hutt's water supply after a reservoir tested positive for E. coli earlier in the year.

Hutt City Council said it started chlorinating the supply for 76,000 residents after a routine test from the Naenae reserve came back positive.

Before that, an outbreak of gastroenteritis in Havelock North in August last year was linked to E. coli contamination.

About 5500 people, or a third of Havelock North's population, fell ill after drinking water contaminated with campylobacter.

The illnesses was linked to three deaths, and three people contracted Guillain-Barre Syndrome, a neurological disorder.

It was confirmed earlier this month that the most likely source of the contamination was sheep faeces that ran off a paddock following heavy rain.

What is it?

E. coli are bacteria normally found in the gut of warm-blooded animals and people.

There are many harmless types of E. coli but some types that can cause disease.

Illness-causing E. coli can be transmitted through contaminated water or food, or through contact with infected animals or people.

It can take about 2-10 days for symptoms to show after the bacteria is ingested.

What are the symptoms?

If someone contracts an E. coli related illness, they can experience stomach pains, mild to severe diarrhoea, and vomiting, as well as a possible fever.

Symptoms can be severe for children, elderly people, or those with weaker immune systems.

When to go to the doctor:

Most symptoms last from a few days to a week. Contact a doctor if:

- You have diarrhoea that isn't getting better after four days, or two days for a child.

- You have a fever with diarrhoea.

- If stomach pains don't improve after a bowel movement.

- If there is pus or blood in your stool.

- If you can't keep liquids down well.

- If you have been vomiting for more than 12 hours. If a baby under three months shows symptoms, contact a doctor immediately.

- If you become extremely thirsty, dizzy, or have a lack of urine. These could be symptoms of dehydration.