I live in a unit in Sydney Australia, I am trying to figure out how to turn off my water so that I can replace the washers on the taps in the basin. Is this possible so that I don't disturb my neighbours? I have looked everywhere inside my unit for a tap which turns off the water but can't find it...
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
There are usually local shut-off valves under the basin specifically for that purpose. If not, I agree that asking the building manager/owner/landlord/superintendent is the most straightforward answer.