Mine froze solid last week when it was cold. Since I don't have them completely full (there is a gap at the top of about 6 inches because the overflow valve is at that level, they were ok.

It's possible that the connections can be damaged and may need to reseal them at some point, but so far, I don't see any major damage. I guess it depends on how thick they are.

Mine expand and contract and are thick enough plastic to handle the freeze. No problems. Just ice!

GGG

I think if rainwater collection is to be taken seriously by those who build houses then some regional standards need to be put in place that treat this like any other utility in the home. That is, it needs to be in some kind of housing that not only keeps it from freezing but protects it from get overly contaminated by debris, insects and other contaminants and maintains the integrity of the tank. These tanks really aren't much to look at, putting them underground is probably a good solution so that outdoor living space is maximized and larger tanks could be used.

In the meantime incandescent flood lamps and being wrapped with insulation could help for brief deep freezes in this area. That way the water can be used for the week or more of extremely dry weather that tends to follow cold fronts.

If you're using a pump and there is frozen water in the connectors then they can break when you go to turn the water on.

Maybe we should get this put on the agenda and discuss it with county commissioners. While we're at it we could fight to make rainwater collection systems mandatory for new construction. Something like this could prevent so much of the green industry from suffering and eases some of the strain on the water system for outdoor watering.