Out of nowhere my jacuzzi tub's cold water pressure dropped to a trickle. Hot is fine. All other faucets in the house work perfectly. Not sure what could make the water go from 100% to 10% overnight.

Hi Sluggosan:

Possible that the washer has loosened and is dislodged and blocking flow out of the valve. Here, you would shut water off to jacuzzi, remove handle, and then remove the stem and inspect the washer. If the washer is loose, you may just need to tighten it. While the stem is out, pulse the water on for a second or two (cover valve with a towel for this) to clear line of any sediment/debris that may have gotten stuck in the valve and then reassemble and see if that fixed it.

If this doesn't fix it then you may need to replace the stem assembly OR check for water volume at the closest cold water shutoff to the jacuzzi. Possible that here, something is blocking the shutoff... ;)

Start by removing the stem unit and see from there.

Let me know if you have questions...

MARK