[LazyPup]

The Standard Atmospheric Pressure is 14.69psi while the code minimum for residential water pressure is 35psi, or nearly twice the atmospheric pressure. This means that it is a technical impossibility for air to get sucked into the water lines as long as the supply pressure is present.

If you have a shallow well with an above ground pump the intake side of the pump is operating at a negative pressure (Below Standard Atmospheric Pressure) therefore if you have a crack in a line or a loose fitting air could be getting sucked into the intake then being pushed through the pump and pressure tank into the distribution system.

If you are on a municipal supply you should contact your service provider and have them check for the presence of air in the mains.