When flow to a faucet fouls up, the first thing to check is the aerator... No, this isn't something you fly with. The little screen that is usually screwed onto the faucet where the water comes out.
However, on a water-fall type faucet, I wasn't sure where to start looking. Especially since the hot water started slow flow long before I had the issue with the cold.
My fear was that the entire pipe in that area might be slowing down from sediment buildup... a fear made greater by the fact that the cold slowed down right after turning on and off the main house shut-off several times while doing other pipeworks. Is the pressure tank so full of sediments that it knocked them loose from turning the valve a lot?
So my first area to check was how much sediment was in the pressure tank.
I connected a water-hose to the drain valve near the tank and watched the outflow in a white bucket outside while hubby turned on, off, on, and turned off and on the electric to the pump as well.
While this poured out a small amount of sediment that must have been in the pressure tank, it wasn't nearly enough to be causing an entire pipe to slow down... especially since the other sinks and tubs didn't seem to have this issue.
So hubby and I removed the pipe to the problem sink and I alternately plugged the end and released the water with the check-valve open. This sprayed more sediment from the pipes, but again... not enough to be causing the flow issues.
I felt up into the pipe attached to the sink and felt more sediment, but it didn't seem to be coming out with a pipe-cleaner. A rough dig with a wad of toilet paper brought out the offending sediment... and... the screen it was caught in!
Since the sink had no aerator screen on the flow side, it had individual screens on each intake.
Removal and cleaning of the screen on each side, and now the water flows like the faucet is brand new. And forcing the water flow out into buckets also should reduce the sediment in the pipes and hopefully the screens will not clog up again for quite some time.
Lesson learned... just because you can't see the screen doesn't mean it isn't there.
Kinda like life... Just because you don't see the problem jamming up the flow of your life, doesn't mean there isn't one there. Sometimes it takes a little digging in the least expected places.