Donations, grants, and other revenue sources will be used to either (1) not borrow as much as we possibly can or (2) help make the annual bond payments.
Think of it like a mortgage. Donations and grants that we receive before we issue bonds are like a higher down payment on your house. Your mortgage is smaller.
On the other hand, donations and grants we receive after we issue the bonds are like getting an inheritance that you use to help with your mortgage payment. We can use those to pay our annual bond payment meaning taxpayers have to chip in less.