If it deems it expedient, the board of trustees of the regional water and sewer district may assess the real estate as provided in the resolution to improve and collect such assessments, or may issue bonds in anticipation of the collection of such assessments before the work is done or contracted for. The board may delay such assessment until the work is completed and upon the filing of a certificate showing the completion of the work assess the real estate as provided in the resolution to improve. Any person so assessed may pay his proportion of the assessment in cash within thirty days from the date of the levy thereof upon due notice being given. If any such assessment is twenty-five dollars or less or if any unpaid balance of an assessment is twenty-five dollars or less, it shall be paid in full and not in installments at the time the first or next installment would otherwise become payable.