A lot of people worry about water. I guess that makes sense as you can't live more than a few days without it, but we really shouldn't worry. When I am doing trips this is how I deal with water.
The things we are worried about contaminating our water are primarily Giardia, and Cryptosporidium. Both cause intestinal distress. There is no real data on how much of the free running water is contaminated in the United States, but it is always best to treat your water*. Some people worry about viruses in the water, but short of 'Katrina-esque' situations, we generally don't see viruses in the water in the US. All the major commercially available filters will get Giardia and Crypto though, so no worries there.
I usually have the ability to carry a lot of water in my boat. On long trips I have the capacity for close to five gallons of water. Three liters in a reservoir for drinking while paddling. A gallon in an MSR dromlite. 2.5 Gallons in an MSR dromedary. I find the 'droms' easy to deal with in the boat and easy to work with around camp, and I like the platypus big zip for my personal drinking water when I am paddling. But how do I treat it? I use a couple of different methods.
I own a sawyer two bag, gravity fed system. It is fast and easy, and I never have to replace the filter cartridge. Guaranteed for a million gallons. I like this because there is no pumping. I was once on a backpacking trip when someone said "I will wash every dish, but I am not pumping anymore water!" So with big groups I like gravity systems.
Sarah and I also used Aqua Mira in Alaska - which is what NOLS uses and how I learned about it. A great chemical system. Mix seven drops of "A" with seven drops of "B". When it turns yellow add it to your water. 30 minutes later you are good to go. It was great when we were paddling past water, and didn't want to get out of the boats to hang a filter bag. Do it all in the cockpit.
For my uses, I don't like steripens. Primarily because they use batteries (or charge via USB) and are an electronic device that can break. They also don't work if the water isn't clear - though you can pre-filter the water and then use the device. They are very light, and very convenient. if you can work around their short comings they are awesome.
I have used the sawyer squeeze, and it is a great product, but it is surprisingly hard to fill the bags. I am a big fan of the MSR sweetwater. Fast, reliable. light. Great option for shorter trips with smaller groups. It is really about finding what works for you.
*unless you are in a life threatening situation. It is always better to treat untreated water, than to die of dehydration.