The GST is a tax on domestic consumption. It is paid when money is spent on goods or services in Singapore.
We do not exempt basic necessities from GST in Singapore, because multi-tiered GST systems benefits the better off more as they spend more on everything, including basic necessities. Such a system is also administratively costly to implement.
Instead, what we have is a fairer and more effective system. We collect GST from all taxpayers, including the higher-income households who spend more, foreigners residing in Singapore, and tourists. We then directly help lower- and middle-income Singaporean households and seniors who pay GST for their expenses, through the permanent GST Voucher scheme and other subsidies/schemes. By doing so, lower-income households pay a much lower effective GST rate than higher-income households; this approach is fairer and more effective, rather than waiving GST for some goods for everyone, whether rich or poor.