Cal. Wat. Code § 51336
Incidental expenses, as used in this article and in Section 52560 include, among other things, the difference in amount between the par value of refunding bonds and the amount less than par for which the bonds are sold, and also the amount necessary to be made available for the payment of interest upon the refunding bonds directed to be sold from the date of sale thereof to the date of maturity of the bonds to be refunded out of the proceeds of the sale.
Amounts assessed for incidental expenses for the difference in amount between the par value of the refunding bonds and the amount less than par for which they are sold, with any interest thereon shall be assessed against the several parcels of district land in the same proportion as the original assessment, or any subsequent reapportionments thereof which secure the payment of the refunding bonds sold for less than par value.
Ca. Water Code § 51336