There are many options for filters that are compact and lightweight. My choice on both the Pacific Crest Trail and the Continental Divide Trail was the Katadyn Hiker Pro. It weighs 11 ounces and you will get about 200 gallons of water (depending on the quality of the water you filter). It has quick release valves which are pretty handy and the output is about 1 liter per minute.
There are many options out there. Would love to hear some input.