The first suspect would be debris in the cold water line. Shut off the cold water shutoff valve under the sink and unscrew the flexible supply line from it. Get a bucket and put it under the valve and turn it back on. If the flow is unobstructed, then your problem isn't there. Unscrew the other end of the flexible supply line and use another sink to run some water into one end to see if water comes out the other end. If that's clear, the issue is in the faucet itself and you may need some air pressure or water pressure to reverse the flow and see if you can't clear it.

I am with Green, I would suspect debris in the shut off valve.

Buy some plumbing tape (teflon tape) to put back on any metal joints before you screw them back together.

Will try to troubleshoot when I get home. Oh btw how do we prevent this from happening in the future? How did the debris get in there?

Thanks!!!

Debris comes from many sources - old pipes (not necessarily from your house).
Grit from water source, etc
Years back, the Smith water heaters had a tube that disintegrated and lots of little pieces of plastic blocking the faucets - even after they back flushed our pipes, we still had debris episodically.

If it does turn out to be junk in the water line,
you might think about having plumber put a very *basic* filter
in main water line coming into the house.
Swap out the filter every 3 - 6 months for a few $$.
This would keep that sort of thing from happening again,
^and^ will lengthen the life of your hot water heater..

Most go bad when very small stones in water line fly
into the tank at high enough velocity to make cracks
in the glass liner.

Once cracked, the tank begins to rust; eventually the tank begins to leak.
No cracks, lifetime might be in decades.
.

City Boy - great idea!

Often you get a little debris in the line during the construction phase or even the manufacture phase of faucets or valves. You will often see instructions to run faucets without the aerators for the first time and that is specifically to clear the debris out before it gets caught in the faucet.

I would suspect it came from your construction or the manufacture of a new line, valve or faucet and you will be fine in the future once you clear it out if this is not a problem you have had before with your old plumbing.

You can also get debris clogging up the cartridge. I've had either the hot or cold side get clogged up on a few bathroom faucets, oddly enough always on faucets that are rarely used.

I've changed out a couple myself, but these days I just call my plumber. It's a quick and easy process if your plumber carries your cartridge in his truck.

Do you soften your water? Do you have very hard water? Some plumbers (most?) only soften hot water so that you aren't drinking softened water... That said, you could get hard water deposits in the cold lines (and those could break off and clog your faucets).

Thanks guys...

We are still at the stage of just trying to figure out the right pipe to buy to flush out the cold water line. LOL! Two trips to the hardware store already but we are getting there...

How do I know if its the "cartridge" that is clogging up? What is that??

oK guys we just did it and tested it close to the supply line. The cold water flow is really low so it is obstructed :(. so I guess there's something in the lines below the supply and it's time to call the plumber? Or should we try anything else?

Unless you are comfortable cutting copper it is time to call the plumber. If you are where I think you are, it is probably the shut off valve.

If you are comfortable cutting copper and you have another shut off downstream, I would cutoff the valve and replace it with a sharkbite which does not require sweating copper together. I have about 1/2 sharkbites and 1/2 sweated valves in my current house and haven't had leak problems with either.

Plumbers aren't cheap but should be a fairly easy fix so not big $$'s.

This happened in our shower but it was the hot water that disappeared. It turned out to be a broken valve inside the faucet lever. My DH figured out how to fix it by watching a youtube video. It worked.

Success! We got our contractor to come over and he unscrewed the anglestop and tried to clear it out. Turns out there was this gross piece of gum (about 1/2" diameter) stuck in the angle stop. Not sure how it got there from the supply line?? Anyway it has been removed and cold water has been restored! PHEW! Thanks everyone.