It’s that little hole near the top edge of some sinks. Its job is to stop your sink from flooding if it fills up too much — the water gets redirected down the drain instead of spilling all over your nice kitchen floor.
They’re super common in bathroom basins, but not something you see in every kitchen sink.

Here’s the interesting bit, according to the Aussie National Construction Code (NCC) and plumbing standards (AS/NZS 3500), you’re not required to have an overflow in your kitchen sink.
Those rules mostly apply to bathrooms and laundries, where a water overflow could cause bigger dramas. Your kitchen sink? Not considered a “wet area fixture,” so the codes don’t insist on an overflow there.
Basically: it’s optional, not mandatory.

If you’re choosing a multi-bowl sink (double, 1.5, or 1.75 bowl), here’s a handy bonus: some act as built-in overflows.

How it works:

• If your main bowl is plugged and filling up,
• and the second bowl is unplugged,
• with a divider lower than the sink rim…

Water flows into the second bowl instead of spilling over. No stress, no mess. Just keep that second bowl unplugged to get the benefit.

Examples include Caroma Urbane II sinks, Turner Hastings Cuisine Inset Undermount with Drainer, and Seima Oros multi-bowl products.

Honestly? For most people, a kitchen sink without an overflow is totally fine. But here’s when it might be worth considering one (or a sink design that acts like one):

• You’ve got little ones or forgetful teens who love to leave taps running
• You’re in a multi-storey apartment and really don’t want water going through the floor
• You want that extra peace of mind (even if you never actually need it)

• Overflow holes can get grotty if you don’t clean them every so often
• Not all sink designs offer them – especially if you’re going for something stone or custom
• Some strata buildings might have their own rules, so it’s worth checking if you’re unsure