I bought this water bottle to take on a month-long trip to China and what a godsend it was.
Even Chinese people cannot drink their tap water as it is totally undrinkable. But whatever you put in this flask comes out totally safe and tasting really good (I filled up from taps and lakes). I saved a fortune in bottled water, stayed hydrated for the duration, reduced plastic waste and was the envy of other travellers.
The best bit is that when it no longer works, it prevents you from drinking from it so you are never in any danger of drinking something nasty. This is the best travelling gadget I've ever owned and I can't praise it enough.