I'm a big fan of the MSR Guardian Purifier... I've had it for a couple of years now and its incredibly fast (especially for large groups), cleans basically any water source, and is pretty robust. The only downside is its very expensive (I waited until it was on sale) and its a bit bigger than other purification methods. I also carry a lifestraw for day hikes and as an emergency backup. Its light, fairly cheap, and is good for a long time...
- I've used tablets and drops - I am personally not a fan of limited supply and the wait time, but they are still used by many for their small weight/size
- I've used the gravity/squeeze bags - which IMO take way too long, but are popular for their smaller weight/size for backpacking
- I've used UV pens - but didn't really enjoy worrying about extra batteries and issues with cloudy water
This is a super slick system, especially for day hikes or trail runs when you want/need to carry a smaller/lighter pack! I've only used it while backpacking, not for day trips yet, but I am so excited that this summer I'll just carry a tiny filter instead of 2-3 extra liters when I'm out doing a 20+ mile day!)
I use the Sawyer Squeeze, and carry (3) one quart bags. I also have the Mini, but the Squeeze is a lot faster for a bit more weight and bulk. I've heard a lot of people complain about the bags busting, and they do, but they weigh next to nothing so carrying empty bags isn't a biggie. I've busted two in the last 8(?) years, so it's not that often. On my last trip, I dropped my soft bottle and poked a hole in it, so I pressed an unused Sawyer bag into service as a bottle, and then later in the trip managed to bust my "dirty water" bag, so I was glad I had the spares. I carry either a one liter soft bottle or one liter Nalgene to drink from. Despite the weight, I can get the Nalgene in and out of the side pocket of my pack easily, where I have to fight with the soft bottle to get it in.
I used the Katadyn Befree system this week on Mt Whitney. Great waterflow and great reviews. It filters bacteria, protozoa and "crud" but not viruses.
That said, if you're hiking the traditional routes at the Canyon (Bright Angel and/or South Kaibab and then going up North Kaibab, you won't need to filter water. There's potable water at numerous places. I do R-2-R frequently (live in Scottsdale) and will be there again in September for a R-2-R-2-R crossing.
Still using my old MIOX generator. Lightweight, compact and tough as nails, and just all eat up with techno cool factor. Uses electricity from C23 photo batteries to hydrolize a brine solution you make from rock salt and raw water. Click a little button one to four times, depending on how much water you need to disinfect. The little bit of water starts to bubble and foam, and the smell of chlorine fills the air. Nearby hikers start sniffing and turn their heads to see where it's coming from. Folks gather around to watch. Dump the solution in with your raw water, wait a few minutes, and you've got clean disinfected water.
Just to be clear for people who may be looking for an actual purifier, the Sawyer Squeeze mini (and original) as well as the Katadyn BeFree are not purifiers but rather just filters. They are both great but they will not purify your water. Water filters and water purifiers are not synonymous.
The MSR Guardian is an excellent water purifier if you don’t want chemical treatments or will be using cloudy water where a UV filter isn’t trustworthy.