No doubt that that USCG/SOLAS certified emergency drinking water is waaaay more expensive. Not sure if anyone has read the specs for testing, but they are pretty impressive.
I think for many of us being able to store some water in a vehicle without worrying about it freezing and bursting on cold nights, or leeching chemicals on hot summer afternoons, and being free from the hassle of constant rotation, is well worth the price for the small amount of water we are talking about.
Would I spend that kinda money for my main water stash at home? Certainly not! But limited quantities for the vehicles? For sure.
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MedB