Individual square shaped modules used in an assembly for underground storage of storm water and other fluid storage needs. Modules are assembled into a resultant square tilling shape for maximized structural strength and material use efficiency. Internal square shaped modules are assembled and encased by external square shaped modules. Internal adjacent modules are in direct fluid communications with one another through a channel-less chamber. Internal square shaped modules drain into square shaped modules chamber where fluid is either stored or drained. Assemblies include various top and side pieces along with access ports for entry into said assembly.
