How to best insulate an exposed waterpipe during the cold season
Insulation only helps keep in heat, but if there is no source of heat (ie: cold water or standing hot water), it will eventually cool and freeze.  Your options are:


Burry it below the frost line (take advantage of geothermal heating)
Install heat tape (electronic pipe heater)
Keep it running (or have it intermittently run; running water won't freeze easily, but this is a huge waste)