The 18-year-old will spend five days consuming only $2.25 worth of food and drink as part of a poverty challenge to raise money for victims of sex trafficking.
She will be joined by others nationwide participating in the global Live Below The Line campaign, which encouraged people to spend five days living on just $2.25 a day - the global poverty line equivalent.
In New Zealand, the challenge was being held from September 23 to 27 and would see participants raise money for 22 different partner charities.
Miss Williams, a University of Otago student, had already raised more than $500 for Tear Fund New Zealand with a fellow Salmond College resident also undertaking the challenge.
They hoped to generate $700 for the charity, which aimed to rescue and rehabilitate victims of sex trafficking in Southeast Asia.
Miss Williams planned to eat porridge made only from oats and water, as well as half a banana for breakfast, two pieces of bread and a sachet of soup for lunch, and lentils or a bland stew for dinner.
''The $2.25 worth of food includes salt and everything, so there's not too much you can glam it up with,'' she said.
She could not accept food gifts during the week, and was grateful she did not have an addiction to coffee.
''I'm a water drinker, anyway, so that does make it easier. I think the hardest thing will be sticking to three staple meals with nothing in between - no night eating or snacks.''
Miss Williams said she would try to maintain her normal level of academic, social and sporting activity despite her restricted diet, and hoped an exam on Tuesday would go well.
She looked forward to enjoying fresh fruit and vegetables, and possibly a batch of home-made brownies, upon completion of the challenge.
''It's just trying to get people aware of poverty. It's such an easy thing to just go about your day and shun like it's not our problem.''
