How dose water get in my tv ariel makeing my tv to go off?

Some TV sets have a "no signal" timer that will shut the set off after 10-15 minutes of no signal condition. This might just be what you are referring to as for the set going off. The cable connections that are outdoors, should be using an outdoor connector. These connectors use a water resistant gel inside the connector itself. Some cable manufacturers use this gel in the cable itself. At the very least, the outdoor connectors should have an "O" ring in it to help keep water from getting into the center conductor area. If your set, or set top box is digital, and you experience a signal loss, there will be no picture. Not like og TV where the signal just gets snowy. With digital, it's either there, or it's not.