For the preppers prepping to live off grid.
Let me know if it can work
Great idea short term and if you don't trust local water. But don't put any long term reliance on rainwater in any one area. We have no idea how climate patterns will change.
There are seasons, that it won't rain for one second in a full month.
That may be the problem you refer to.
So i think you need dozens and dozens of vases to collect enough water for one full month in just a few hours of raining.
You need to be able to collect at least 30-40 Lt when it rains, to be prepared to one month of drought. (Plus the water for showering)
And when you need to drink, you fill a glass and purify it with silver at the moment.