Each forest preserve district may create, maintain, and increase a separate fund to be known as the “Endowment Fund” to pay all costs and expenses incurred or anticipated by the forest preserve district for the long-term maintenance and improvement of forest preserve facilities and lands, and for the future purchase of real property. Only one “Endowment Fund” may be created by a forest preserve district, but the fund may provide for the collection, maintenance, investment, and expenditure of monies for more than one purpose. All revenues deposited in the Endowment Fund shall be designated by purpose and appropriated and expended for the purpose for which it was designated. No appropriation in the Endowment Fund shall lapse, and the monies received and designated for a specific purpose shall not become part of the general funds of the district or considered an asset available for appropriation for another purpose in a subsequent year unless the purpose for which the monies were originally appropriated has been completed. Revenues deposited in the Endowment Fund must come from private sources, whether received before, on, or after the effective date of this amendatory Act of 1995. No revenues shall come from any Federal, State, or local government source, except for those received as a result of agreements obligating the district to the long-term maintenance of improvements constructed on district lands. The Fund shall be audited annually by a licensed certified public accountant.