It depends on your travel style. In the US West, I enjoy "dispersed camping," easy to do on public land. You might find an otherwise perfect site with no water other than a suspect source of surface water, especially in cattle range country. If you have the option to treat water, you might have many more excellent camping options, even just off pavement. Many would not consider this kind of camping and for them water purification would be a silly thing to carry.
As an alternative to a filter, consider AquaMira drops--lighter and cheaper. You'll probably never need it, and it's easier to justify carrying less.