In addition to the powers otherwise provided for improvement districts under this division, the board shall have the power to levy a utility tax, as provided by this article, on every person using water within any of the improvement districts established by this chapter or on every person using water within the service area of any retail water purveyor within any such improvement district.

Nothing in this article shall be construed as imposing a tax upon any person when the imposition of such tax upon that person would be in violation of the Constitution of the United States or the Constitution of this state.

The board shall enforce the provisions of this article and may prescribe, adopt and enforce rules and regulations relating to the administration and enforcement of this article. The board shall not prescribe, adopt or enforce any rule or regulation which has the effect, directly or indirectly, of altering the terms and conditions of service of a service supplier serving the general public. Rules and regulations prescribed and adopted by the board shall not be inconsistent with procedures established from time to time by a service supplier serving the general public for the purpose of billing, collecting and accounting for charges in the conduct of its business.

Whenever the amount of any tax has been overpaid or paid more than once or had been erroneously or illegally collected or received by the board, it may be refunded, provided that a claim therefor in writing is filed with the board within two years of the date of payment.

Notwithstanding the provisions of Section 72072.11, a service supplier may claim a refund or take as credit against taxes collected and remitted the amount overpaid, paid more than once, or erroneously or illegally collected or received when it is established in a manner prescribed by the board that the service user from whom the tax has been collected did not owe the tax; provided, however, that neither a refund nor a credit shall be allowed unless the amount of the tax so collected has either been refunded to the service user or credited to charges subsequently payable by the service user to the person required to collect and remit.