My bathtub's cold water facets drips out if the knob handle when the water is running. No prob when the facet is turn off...

What needs healing? Is it fatal? Should I call P-911 or are we talking plumbing 101?

Thanks in advance...

Remove the knob and the chrome cover plate. You should see two brass nuts on the stem. The top nut is the bonnet packing nut. Turn on the cold water until it leaks past the stem. Now tighten the bonnet packing nut clockwise until the leaking stops. STOP TIGHTENING! Over tightening will make it hard to turn. Put everything back together. Good luck, Tom