Glossary
Pressure loss
The drop in water pressure between a meter's inlet and outlet caused by the meter itself. ISO 4064 and OIML R 49 set a maximum pressure loss across the meter's working range.
Why it matters
Where supply pressure is already low, as at the tail end of many networks, a high-loss meter can leave upper floors short of water. Check the stated pressure loss at the expected flow when sizing meters.
Source
ISO 4064-1:2014; OIML R 49-1:2013