Tap water is universally safe for drinking and cooking in New Zealand, except for exceptional circumstances. Major cities have regulations set in place to ensure the major contaminating organisms are removed, to supply a safe drinking water level.
Nearly all residential areas offer safe drinking water from the tap. There may be a one-off case where local water is not safe to drink. However, this will be indicated and you will be warned in these areas.
In fact, New Zealand's cities have some of the world’s best tap water, offering better quality than most major international cities. New Zealand's water supply is currently chlorinated, so it may taste quite different to some international visitors. If the taste is not to your liking, leave a full jug of water in your fridge overnight as the chlorine naturally dissipates.
The majority of our tap water is also fluoridated. However some consider fluoridation a negative measure to their health, so some areas have floride free water.
Avoid buying plastic water bottles, and be sure to grab yourself a reusable or sustainable bottle, and make the most of our high-quality water supply.