If you experience air in your plumbing system, it is likely to be the result of the water being off and then turned back on. When the water has been turned off because of a water leak, either in the street or in your plumbing system, the air is introduced into the pipes.
When repairs have been completed and the water is turned back on, this air is pushed to every fixture in the house. It remains there until the faucet or fixture is opened to allow the air to escape.
When relieving this air, do it slowly, barely opening the cold water side on your fixture. Leave the fixture open for several minutes until all of the air and sediment has been removed.