Section 58D. If a rate or charge for which a lien is in effect under section fifty-eight C has not been added to or committed as a tax and remains unpaid when the assessors are preparing a real estate tax list and warrant to be committed by them under section fifty-three of chapter fifty-nine, the manager of municipal lighting shall certify such rate or charge to the assessors, who shall forthwith add such rate or charge to the tax on the property to which it relates and commit it with their warrant to the collector of taxes as part of such tax. If the property to which such tax or rate relates is tax exempt, such rate or charge shall be committed as the tax.