The water inlet pipe is 2 inch copper. The water supply is municipal. I want to install a leak detector that requires only a one inch pipe. I plan to cut the two inch copper pipe and install one foot of one inch copper pipe and then return to the 2 inch pipe. This will be done in line. The two inch pipe supplies a house and farm. What effect on will this have my water pressure and flow rate?
First, check on what @ThreePhaseEel said then, as a "rule of thumb", a 2" pipe can carry the flow of 4- 1" pipes, so the 1" pipe will only carry 1/4 of water of the 2" supply pipe. Under a no flow condition the pressure will remain relatively the same but there will be reduced maximum flow and reduced pressure when a large flow is utilized.