I'd want a backup method in case it broke or failed.
Seems to me the only way you would know it failed is if you become ill with a water borne agent.
Yep. There's no reliable way that I've ever heard of to test a filter unless you've got access to some sophisticated lab equipment. There's no "home kit" that you can buy.
I guess you just have to replace your filter periodically or use other means. The lack of a means to verify that the darn thing works is a HUGE negative on filters.
HJ