It really is not relevant whether the water falls from the sky, is from the local river, is collected from low area pools or ponds or flows from the utility pipes, ALL water is a SHTF situation should be considered suspect.
89% of the deaths from disease world wide are due to a water related issue, either parasites or microscopic agents or chemicals. It does not have to be a nuclear war, tsunami, fire or flood, it only takes a few days for diphtheria, typhoid, cholera or dysentery to start breeding in polluted water.
I know you don't think those things are relevant in a first world nation but in GB you are only meters away from someone that just got off the plane from Ziare yesterday, or some equally strange place like Brighton.
It took Omicron variant about 8 days to get from South Africa to London.
Brita filters are yuppie fridge water containers and not efficient "water filters". You get about the same filtration from a coffee filter as a Brita.
Berky filters were designed for use in remote regions of the world where the water will kill you on sight. No kidding, over most of Africa you can die from just wading in the water in your bare feet!
You can collect muddy river water from a cattle pond in the Congo, run it through a Berky, and drink it safely.
Thanks to the kidney dialysis technology we now have, (the tech is the same) there are fine filter cartridges available such as the Berky and the small Sawyer, and the Life Straw.
The Sawyer filter is the standard of adventurers world wide these days. Here in the States long distance hikers use them universally and no longer feel the need to carry reserve water in their packs. They just top off their supply from any available source and drink directly through the filter. We used to have to carry several liters of safe water and it was a load!
The Sawyer and life straw cost less than a carton of cigarettes or a case of good beer, or even a bit of that exotic coffee you insist on, and they will give you 100,000 liters of safe water, and they can be carried in a jacket pocket.
My Berky is good for several hundred thousand liters. I forget how many but it was a 10 year supply for me. The two filter cartridges were about $40, US money
https://www.youtube.com/watch?v=_gx2nDtEDXo