The 1992 law which governs the application of IVA says that those services which are continuous over time should be charged at the rate valid at the time of billing.
As you know, IVA was increased to 18% on the 1st July. That rate applies to telecommunications, electricity and gas; water is now charged at 8%.
That means that any bill you receive for utilities after the 1st of July or has a payment date after the 1st July even though it is for the period prior will show the new rate. It might seem unfair but it is legal.