A pine tree does not need constant watering unless it is freshly planted, in which case it needs water two to three times a week for a year. Fully grown pine trees capture most of the moisture they need in their soil.
Fully grown pine trees only need to be watered during extreme dry spells. A pine tree can still be watered to make it stay green and healthy during the year, but care needs to be taken to not overwater. Pine trees do better with deep and slow soakings as opposed to simply dumping a bucket of water on the ground under them.