The best thing we have right now is ANSI standards 42, 53, and 401, NSF will issue certifications for individual contaminants listed in these standards. The issue is there are so many things to filter out of water that it's extremely expensive to test for all of them, so most companies pick several that are common and certify for those. If you know what you need to filter then you can look for filters that are certified for that thing, but if it's something uncommon then you might not find anyone who's tested for it