Originally Posted by nicuribe
I'm now faced with the prospect of installing cistern tanks (at least 1,000 liter capacity) on my roof so as to first store the water
This tank could weigh 2200 pounds.
The water company can supply you with likelihoods of X continuous days without water or with low pressure and the NWS may be able to supply you with rainfall data.
The recent past may predict the near future.
I don't know if the WaCo will give you these data because it makes them look bad. You might have to write to your state's attorney to pressure them into giving you this info.
You can then size your tank appropriately, based on, let's say, a 50%, 95%, or 97.5% chance of always having water.
Normal water usage is 70 gals per person per day.
You might want to consider a well. Half the wells in the US are between 80' and 240' and 95% are between 25' and 470', but I have only one sample of a price: 12 kilobucks for 520' well. Avg. depth is 200'.