(a) If the revenue and income from the properties and facilities of the district are encumbered under the provisions of this subchapter, the expense of operation and maintenance necessary to render efficient service of the properties and facilities shall be a first lien and charge against the revenue and income. The first lien shall be prior to and superior to the lien of the encumbrance.
(b) No encumbrance shall be foreclosed because of default of the district until the default has existed for a period of 90 days and notice of the default has been served on the commission.