New Zealand compared to the rest of the world has an amazing plumbing network and code. We have drinkable lead free water that wont make you sick we have fantastic pressured (in high density places) and we have ample supply.
Having personally worked all over the world on plumbing systems I can comfortably say this is due to our strict code and licensing system.
Checking if your plumber is actually a plumber is very easy to do. All you need to do is Go only to PGDB (Plumber, Gasfitter and Drainlayer Board) website and either type in your plumbers name or license number and a page will pop up with there current licenses. Here is the link
https://www2.pgdb.co.nz/public-register?login=Trade+Login
The dangers of hiring a handyman can be drastic and you get end up getting everyone in your household very sick.
Weather you in Mount Albert, Meadowbank, Mount Eden or Grey Lynn you should always check the register to find out who your dealing with.