In addition, held the High Court recently, you are entitled to inspect the source documents underlying the account (a source document, held the
Court, being “a tax invoice or any document of prime entry no matter what label it carries”). 

If you have difficulty in getting what you need from the municipality, seek legal assistance – the Court in this instance ordered that the applicant be allowed to inspect all source documents, and clearly would also have ordered the production of original invoices if that had not been rendered impossible by a technical failure in the municipality’s billing system.