Gabriela,
As Mohamad suggested it depends on the location (availability of water), facility density, building material, occupance, hydrants availability, residency type etc. and different city/municipality has different requirements. Insurance company has their own requirements. No one in the forum will suggest you the exact number as this depends on your criterion.
AWWA M31 manual will give you some idea about fire flow requirements
This link will show you the TOC of the manual.
http://www.awwa.org/portals/0/files/publications/documents/toc/M31ed4.pdf
To understand modeling and theory/logics behind it, always refer to books. Click on the "Books" in my signature and try to find/buy one or two books.