It is the same in most states an is really a maximum we should be using. As there are so many variables the actual individual usage varies greatly. A lot of people make statements of less useage, and while that is fine, the figures are calculated on a property having scheme water usage only.
Things taken into account are 2 reasonable showers per person per day, garden water (which is generally the biggest user if you have big lawns), average laundry washing loads, generic use for washing cars etc, average toilet flushes, air conditioners. If we look at it the 155l per person is quite generous. Of course if you own a pool you may not think so, but exemptions can be obtained for initially filling a pool or refilling.
We are way under, I think we average about 25-30 litres per person per day or less as we have rain water and a bore for the garden.
It is something that is relative and there is no clear answer. Ultimatally we should use as little as possible anyway.