Cal. Wat. Code § 35520.33
When a district has levied an assessment and it appears to the board that the assessment or some part thereof, together with the interest thereon, will provide an amount greater than is required to meet all obligations incurred, or to be incurred for, the purposes for which the assessment or part thereof was levied, and if no bonds secured by the assessment are outstanding, the board may, by resolution, declare its intention to cancel all or any portion of the assessment, including any interest thereon, or all or any portion of the interest.
For the purposes of this section, the term "assessment balances" means the assessment and the interest thereon, and the board, in the manner and subject to the limitations provided in this chapter, may cancel any part of the assessment balance, including all of the assessment and the interest thereon, a part of the assessment and the interest thereon, all of the interest on the assessment, or a part of the interest on the assessment.
Ca. Water Code § 35520.33