Queensland has some of the strictest plumbing licensing rules in Australia. The list of work you legally cannot do yourself is long. Get it wrong and you can void your home insurance, lose any sale contract, and face fines from QBCC.
What you can legally do
Replace a washer in a tap. Clear a blocked sink or toilet with a plunger, hand auger, or chemical cleaner. Replace a shower head or hand-held shower hose where it screws on to an existing outlet. Replace tap handles (the decorative top) where it just unscrews. Replace a flexible water connector if you can do it without altering the pipe.
That is about it. Even replacing a full tap assembly where you cut into the supply pipe is licensed work in Queensland.
What you cannot do
Anything involving cutting, soldering, or joining water supply pipes. Anything connected to the sewer system, including replacing a toilet pan or installing a new vanity basin. Anything to do with gas. Hot water system installation or replacement. Backflow prevention devices. Anything that goes through a wall, floor, or ceiling cavity.
Why it is worth following
Two reasons. First, dodgy plumbing causes serious damage. We have seen DIY hot water installs that flooded houses, gas connections that leaked into roof cavities, and burst joins that destroyed downstairs ceilings.
Second, your home insurance often excludes damage caused by unlicensed work. Same with sale contracts - an unlicensed install can void the warranty on a brand new hot water system.
What it actually costs
The savings from DIY plumbing are usually smaller than people think. A licensed plumber replacing a tap is $80 to $150 including the part. You would spend $30 to $60 on the part yourself plus an hour or two of your time, and that is assuming you do not damage anything. For most jobs, the time saved is not worth the risk.
The grey area
Replacing a kitchen mixer where you are swapping like-for-like and only undoing flexible connections technically requires a licensed plumber in QLD, even though many people do it themselves. If you are selling or making an insurance claim, errors here matter. If you are staying in the home long-term and you are confident, it is a low-risk job.
When in doubt
Call a licensed plumber. The peace of mind is worth $150.