When a faucet has a weak or intermittent flow, the problem is often with the aerator. Aerators contain a fine wire screen that mixes water with air to provide an even flow. Over time this screen can become clogged with mineral deposits or debris, reducing the amount of water coming through.
To solve the problem, unscrew the aerator from the end of the faucet, and soak it overnight in a cup of white vinegar. The acid in the vinegar will dissolve any deposits and make the aerator as good as new.