If your Delta faucet has a loose base, there are a few things you can do to tighten it. First, try tightening the screws that hold the baseplate to the counter. If this doesn't work, or if the screws are already tight, you may need to replace the O-ring that seals between the baseplate and counter. To do this, remove the handle and escutcheon plate, then unscrew the retaining nut and pull out the old O-ring. Install a new O-ring of the same size and shape, then screw on the retaining nut and reassemble the rest of the faucet.