I'm attempting to add an under-sink water filter to my existing wall-mounted kitchen faucet. There is no shut off valve in the sink cabinet for the wall-mounted faucet. The 1/2" copper cold water supply line for the wall-mounted faucet runs straight up the inside of the wall, turns 90 degrees, comes out of the wall and connects directly to the wall-mounted faucet (i.e., the faucet body itself connects directly to the copper supply line coming out of the wall; there is no flexible supply line between the faucet and the copper supply line). The water filter assumes you have a shut-off valve and a flexible supply line from the faucet that would connect to the 3/8" compression fitting on a typical shut-off valve.
Since I have neither the shutoff valve under the sink nor the flexible supply line from the faucet, here's my plan: I have no problem accessing the 1/2" copper supply line in the wall so I want to cut the supply line, attach a pipe at 90 degrees that comes into the kitchen sink cabinet, and then attach a standard under-sink shut off valve. Then I will connect the water filter to the 3/8" compression fitting on the shut-off valve.
The faucet itself will still be connected to the 1/2" copper supply line and so I would have to connect that supply line back to the 3/8" compression fitting on the water filter. If I do that, though, what I will end up with is a 1/2" water supply line TO a shut-off valve with 3/8" compression fitting TO water filter TO 3/8" compression fitting (built into the water filter) TO a continuation of 1/2" copper supply line TO the faucet.
My question: does going from the 1/2" supply line down to the 3/8" compression back to the 1/2" supply that attaches to the actual faucet going to cause a pressure or water flow problem? If so, any other ideas on how to tackle this?