Brisbane's water crisis affected by population growth?

I've toyed with a theory about Brisbane's water crisis over the past few months that goes something like this: we have a weekly influx of 1500 people coming to live here permanently, and they use water like the rest of us. At that rate, even with arbitrary water restrictions of 140 litres per person per day, our water needs are increasing at a rate of 1.47 million litres per week. By the end of one year of population growth at that rate, our water needs have increased by 76.44 million litres per week.

Our "level 5" water restrictions are meant to save us 48 litres per person per day. If the current population is 2 million people (which is an overestimate) level 5 water restrictions will be overtaken by population growth and increased water demands in just over a year.

Mokalus of Borg

PS - I did some calculations on required rainfall for water tanks too.
PPS - But I'm not confident enough to post them.