If you just want to sip from a stream or filter water from a bottle as you're hiking, get a Sawyer mini. (It's better than the life straw, I think, in every measurable way. Maybe not weight, but every important way.)

If you need it to filter viruses or radiation, then upgrade accordingly. Water-born viruses and radiation are not typically an issue in North America, by the way ... but hey, it's good to be prepared, right. This is the only filter I know that does radiation: https://www.amazon.com/Water-Bottle-Filtration-System-Contaminants/dp/B006AVLS22/ref=sr_1_2?ie=UTF8&qid=1498568450&sr=8-2&keywords=radiation+water+filter

There are low-flow pumps that will filter viruses (https://www.amazon.com/Survivor-Filter-Purifier-Emergency-Nanofiltration/dp/B00QFXGSIY/ref=sr_1_1?ie=UTF8&qid=1498568633&sr=8-1&keywords=virus+pump+water+filter) This thing it tiny; fits in a cargo pocket with room to spare. You're not going to provide water for a whole camp, however; it is very low-flow. It also doesn't feel like it will last more than 4 seasons.

Berkey gravity filters are super convenient, except they are large. Upgrade to the black filters (which filter viruses). If you go to their website, check out the "scratch and dent" area for huge deals. Otherwise you may find better prices for Berkeys at https://edenvalleyfood.com/