Well the pipes (main) shouldn’t really be outside. If they are outside they have to be below the frost line and generally come below your basement or ground level via DC WASA. If they are inside they should be in a conditioned space or heated. You could try heating the pipe with a wire from your local home store and since its probably copper, the heat would carry. If you are just talking about a hose spigot outside, you need to shut it off from inside and empty any retained water.
Pipes generally dont freeze outward and break but what happens is they cause damage inside your house because of city pressure. A small trick in the meantime would be on very cold days to leave a tap on inside your house at a very low pressure. This wastes water but for one day you could always keep a big bucket and water plants with it and it could help prevent major damage.