I'd stay away from a cistern. There's a much higher chance for contaminated drinking water with a cistern (affectionately known as bird drop soup.) While you can filter water to render it potable, there is a fair amount of upkeep in doing so and a problem could go undetected for quite some time. Plus, with a cistern you're also relying on Mother Nature to provide the rainwater. Talk to a well driller about your particular geographical area-if there is commonly good plentiful water deeper or if installing larger storage tanks would provide you the extra water you need for those high use times using your current well. A deep, properly installed well may be your best bet.