Arsenic occurs naturally in the Waikato River. File photo. Photo: RNZ / Cole Eastham-Farrelly
Auckland's water provider says the supply from the Waikato River will be tested every day, to keep an eye on arsenic levels.
Slightly elevated - but safe - levels of arsenic have been confirmed in Waikato and Auckland's drinking supply.
Watercare chief operations officer Mark Bourne said arsenic occured naturally in the river and it was not unusual to see low levels in water samples.
"What is unusual is seeing it as this level - we've been sampling the Waikato river since 2002 and its the first time we've ever seen a result like this."
He says sampling would be done daily until the arsenic returned to normal levels.
Bourne said Watercare's first response to the elevated levels of arsenic was to reduce the volume of water produced from the Waikato treatment plant.
"The volume that was reduced there was made up from other water supplies, so there's no need for Aucklanders to be concerned about either the quality, or the quantity, of water that's available."
He said testing was under way to determine the location point of the contamination - which will help to determine what caused it.
National Public Health Service regional clinical director Dr William Rainger said drinking water with slightly elevated levels of arsenic for a short period of time was unlikely to affect people's health.
"People who are drinking water sourced from the Waikato River do not need to be alarmed. The limits in the New Zealand Drinking Water Standards are based on the level of risk from a lifetime of drinking the water."
