The Hazen-Williams equation is an empirical formula regarding irrecoverable frictional losses in piping. This method of estimating frictional losses is only valid for water and has a long history of use in the municipal water industry and fire protection industry. Users can specify pipe friction in AFT Fathom by choosing the Hazen-Williams option and entering the appropriate Hazen-Williams factor. Using the Hazen-Williams equation enables users to be compliant with NFPA 13 and congruent with NFPA reporting standards.