Brita makes a charcoal filter that's widely available, at least here in the States. They claim it improves flavor. I don't know how effective it is at removing heavy metals, but you'd probably be able to find more detailed information on them online. The filters fit down inside a water bottle, which can be either their own special made bottle (heavy) or just a reused disposable water bottle with a pop-top cap/spout. The cap holds the charcoal filter in place and creates a tight seal when you screw it on.

I'm not lucky enough to be one of the majority that enjoy clean chemical free water on my local trails. The areas most accessible to me have a history of mining and ranching, so heavy metals and other pollutants are a potential concern unless I take a road trip. The best practice around here is to cache your water (easy to do since the trails are crisscrossed with county and forest roads).

ETA: A quick note about the Sawyer Mini. They clog really fast, sometimes after (or during) a single bottle/bag of water being filtered, depending on the quality of the water you're filtering. That's not that big of a deal, because they can be back-flushed pretty easily in the field. I found it to be a big hassle though, when I was using the included syringe. I discovered (saw it on Youtube) you can use one of those Smartwater flip-top spouts on the top of your clean water bottle to back-flush, and now I don't mind so much. I just give it a quick squirt every time I filter whether it really needs it or not.

EDIT: It turns out Brita ONLY claims the bottle filters with remove chlorine and particulates, not heavy metals. https://www.brita.com/why-brita/what-we-filter/