If smoking inside public buildings is prohibited by law in your state or locality, acquire a copy of the law or regulation to confirm its alignment with LEED requirements.
The building's original system design specifications and airflow rates are not relevant to this prerequisite. Designing a system to achieve ASHRAE compliance does not mean that the system is delivering airflow at those rates under current operating conditions.
For mechanical and mixed-mode ventilation systems, follow the guidelines specified in ASHRAE 62.1-2007, Section 6 (detailed below) and use the provided 62MZCalcs calculator to determine ASHRAE-compliant ventilation rates for each air-handling unit and zone in the building.
For naturally ventilated buildings, follow the guidelines specified in ASHRAE 62.1-2007, Section 5.1 to assess compliance with the requirements. If your building has the proper ratio of operable windows or roof openings to floor area as described in the ASHRAE standard, you are likely to be able to show compliance. You may also show compliance by meeting the requirements of EQc1.3:
A graywater collection system or other source of non-potable water may require a moderate investment unless a readily available source exists, such as a municipal water reclamation plant.
Sub-meter irrigation systems to track water consumption and efficiency. Review irrigation system sub-metering records to check for leaks or other malfunctions that may be leading to excessive use of potable water.