A person who serves on the governing body of a district is immune from civil liability and is not subject to suit directly or by contribution for any act or omission resulting in damage or injury if such person was acting in good faith and within the scope of his official capacity, unless the damage or injury was caused by willful and wanton or grossly negligent conduct of such person. Nothing in this section limits or modifies the duties of such person to the district. As used in this section "official capacity" means any decision, act or event undertaken by the district in furtherance of the purpose or purposes for which the district was formed or any ancillary or additional purpose authorized by law.