The county shall impose tolls and other charges for use of the project in amounts that are sufficient to:

1. (1) pay operation and maintenance costs of the project;
2. (2) pay principal and interest when due on the bonds;
3. (3) establish a reserve fund if required; and
4. (4) establish an adequate depreciation and replacement fund.

Acts 1995, 74th Leg., ch. 165, Sec. 1, eff. Sept. 1, 1995.