Water filtration doesn't get much more convenient than the BeFree filter from Katadyn. Compact and extremely easy to use, it's essentially a sturdy sports cap with hollow fibre filter built in. Ours came with a 0.6 litre flexible bottle to attach the filter to but other sizes are available right up to a 2 litre camp friendly version. You collect water in the flexible bottle before either sucking clean water directly out of the cap or squeezing it into a pan, hydration bladder or whatever else you fancy. All this simplicity means that the BeFree is not only very light (70g empty) but also folds down to a fist-sized package when not in use.
Although not compatible with regular bottle threads we regularly use ours to top up bike bottles and hydration bladders on the move, as filtering through it is a fast and painless process. In fact, the bag is where the real innovation lies and where the BeFree elevates itself against the competition - it makes a great personal water solution but also allows you to fill yer boots and anything else you care to decant into with lovely clean water.
The filter has a rated lifespan of 1000 litres, removing bacteria and protozoan cysts (yum), but not viruses so you still need to take care and be aware of the water supply. Any major sediment clogging the filter can be removed by shaking the bottle or swishing the filter in water to remove, but as time goes on the flow rate will inevitably reduce as the fine filter slowly clogs. For our test period though it performed admirably, just take care of that fragile bag to prevent punctures and tears.