Ceramic-based filters like Katadyn or MSR, if you are going to be moving. Do NOT use any paper or membrane based unless you are filtering from a well. Katadyn also make "Expedition" version for larger groups. Size of a bicycle tire pump.
Problem in unknown or traveling situations is often mud or other contaminants. Paper-type filers cannot be cleaned like ceramic.
Have bet my life on Katadyn ceramics many times in remote parts of Sub- Sahara Africa. Handled extremes of pond-scum, algae-covered stagnant pools, standing rain-water in jungle, and down-stream from cattle crossings (grossest!). Both hand- filter and expedition versions. Carry the hand version plus 1-2 spares in my BOB as essential. Truck has Expedition version plus spares.
Get yourself some used 20-liter Swiss Army rubberized water bladders to hold clean water (eBay). They are nearly indestructible. Have carried them in jungle, desert, and on bed of trucks with guys sitting on them.
In my opinion, a "complete" portable water system includes a couple foldable water buckets (to carry unfiltered water), Katadyn or other high-end ceramic water filter plus spares, 3-liter camelbacks (preferable mil-spec), and 20-liter (5 gallon) Swiss army surplus water bladders.
Only thing the ceramic filters won't deal with is viruses and cholera. Has handled water containing dysentery, worms, and ghiardia with no problems for me. If cholera a danger, best to boil for 5+ minutes (full boil for 5, not just heating up), then filter too (takes out particles & mud). Or chlorine-based tabs or drops or bleach (2nd best, my opinion, but functional), then filter.
Btw, in East Africa, we calculated 1 liter per person, per hour - walking or riding. Just as point of reference. Don't know what military calculates - that was our experience. So 30 mile walk @ avg 3 miles per hour (incl rest stops) = 10 hours = minimum 10 liters per person needed to carry, or to find along the way. During dry season, means carry that much on your back, plus gear. Not fun, but necessary.
Trust me. Running out of water in middle of 30 mile hike is NOT an experience you ever want to have when the temps are over 110.
Last thing we often do, since dehydration is as much a risk as dysentery from bad water - we carry powdered Gatorade or similar. Diluted (never full strength), helps with hydration and taste of water from the rubber camelbacks. The sugar in Gatorade is heavy, so we keep the amount carried to minimum.