How do I shut off the water to my apartment?
1) Have a look under the kitchen sink. If OZ practice follows UK practice, this is the place in a home where you expect to find the main stopcock (regardless of whether it's the point in a home nearest the road etc). It's usually hidden behind a bottle of bleach you'd forgotten you have. 

Whenever I change taps I install an isolating valve under the basin (builders leave them out to save money) so that I can subsequently work on a basin without emptying the cupboard under the sink and warning the family to cross their legs for a while.



2) Ask a neighbour