My relatives will be travelling in North America, UK, and Hong Kong. For environmentalism, they do not use bottled water, and need a water filter that:
removes chemicals, metals, and pathogens. They will always boil any filtered water as extra precaution.
can be transported (i.e. no installation or plumbing changes needed)
are not jug/pitchers (e.g. BRITA, Mavea, Pur) because 'They can reduce chlorine, but they are not the best home water filters for removing VOCs, fluoride, heavy metals and endocrine disruptors.'
These should be non-electrical (question for electrically powered filters here)