Conn. Gen. Stat. § 7-237: Sinking fund.

The legislative body shall provide for the establishment, from the net revenues of such waterworks system, of a sinking fund for the payment of the bonds and interest thereon and any charges connected therewith, plus ten per cent of the amount required for such payment, as a safety margin. Any surplus from the bond proceeds over the cost of establishing the system shall be paid into said sinking fund.