In certain parts of Australia, summer temperatures can exceed 40C. Domestic water meter performance under these extreme conditions is not well understood. The internationally adopted standard for pattern approval and verification (OIML R49-2 2006) does not require determination of the influence of both elevated water and ambient temperature on the error of measurement of the meter. A study was therefore undertaken to investigate these aspects using three positive displacement mechanical meters: two new 20mm nominal diameter (DN20) meters and one using 32mm nominal diameter (DN32) meter.