Water separation from diesel fuel is a critical requirement for modern diesel engines. The main reasons are: corrosion, wear on the fuel system, irregular combustion and acceleration of microbiological growth that clogs filters, pumps and prefilters. Due to this, agencies regulate water content in diesel (like DIN EN590 ) and biodiesel (like DIN EN14214 ). Also international institutes release standards to define the correct procedures, equipment and boundary conditions to confirm water separation filter efficiency (like ISO 4020  and ISO/TS 16332 ).If you consider the Brazilian diesel conditions and fuel system configurations, the existing specifications, procedures and boundary conditions don't represent actual field conditions. The key differences are water droplet size, flow rate, temperature, biodiesel content and fuel aging effects which all impact the water separation properties. Due to these factors, fuel systems should be developed and validated for regional conditions to ensure proper durability and/or proper function in light of these different field conditions.This paper studies the influence of different factors on the water separation filter performance and proposes a new specification for validation testing. This information leads to more robust components development and generates know-how regarding local Brazilian fuel conditions.