def _calculate_conductivity(row):
    """ formula from https://in-situ.com/wp-content/uploads/2015/01/Specific-Conductance-as-an-Output-Unit-for-Conductivity-Readings-Tech-Note.pdf
    """
    r = 0.0191
    return (row['water_specific_conductivity_mS/cm'] * (1.0 + (r * (row['water_temp_C'] - 25.0))))