For domestic water systems it's required where there is a direct connection to the main supply to prevent back-flow and possible contamination of the public supply in the event of a pressure failure in the supply. Your system, like mine is quite new and plumbed direct into the supply, without a header tank so requires a NRV. New outside taps plumbed into the rising main must have a NRV. Older domestic systems have a header tank where there is an air gap between the supply (ball valve) and the contents of the domestic system so back-flow cannot occur.