Are you in an area that quakes with the fire rating nudging up to EXTREME by July? What are your fire insurance rates like? If you installed a cistern that was equipped with a hydrant valve that firefighters could hook up to to aid their efforts, could you receive a fore discount? These are all questions to ask.
Where we live in the Highlands of Victoria BC, we have had to use our multiple cisterns to irrigate and dampen the surrounding landscape a few years back. Our well would not have been able to keep with its flow rate of 6 gallons/minute – but the three irrigation pumps with garden hose fittings could push 50 gallons per minute and thus douse the embers that were falling all around as a neighbours house burned.
Check with your municipality and ask what volume is useful, and what valve they can hook up to.