Those last 2 sentences contradict themselves, don’t they? (Storing tap water for a few weeks? And observing use-by dates)
You can actually of course store tap water in your fridge, ideally in a metal, not plastic, bottle, but I think the quantities you might need to cover cooking as well as drinking would necessitate a big fridge!) but given that the water companies distribute big containers of drinking water when the supply is threatened or cut off, I don’t see the problem.
How, out of interest, do you see most gardeners having their water issues sorted ?
Water butts will only store rain water which means it has to rain, hosepipe bans might last well into this winter so sprinklers are out, perhaps rethink the whole idea of gardens?
Personally I think agriculture and our food supplies are a much greater problem than my petunias or lawn and this applies right across Europe and beyond.
More and better reservoirs, better planned, better managed and better maintained infrastructure must lie at the root of managing our future water supplies.