I've been reading a lot of product reviews, and filter/pump solutions seem to be very high maintenance, very heavy, or both. Are there any lightweight filters which can be relied on for many liters of water without requiring lengthy clean times, lots of extra cartridges, and/or spare parts?
I'd prefer a recommendation from someone who has used one on a lengthy hike (one requiring more than 20 liters of water filtering over several days).
Without getting into any specific recommendations, pretty much any decent water filter you can find will get you through well more than 20 liters and several days.
By decent, I mean the standard ones you will find at a good outdoor shop: MSR, SweetWater (now also MSR), Katadyn, PUR.
I've used filters with large groups (10 people) for 8 days. Assuming 4 liters a day, that is 320 liters on one trip... And then I used the same filter for the next trip... repeatedly.
Make sure you get one with a filter that can be cleaned -- and clean it (esp if filtering silty / dirty water). A good filter should have a wear indicator to let you know if you've cleaned it so many times it might not be effective.
I've used the Platypus GravityWorks filter with great success and found it to be reliable, easy to clean and it filtered water quicker than any hand-pump filter I've ever used.
What I really liked about this filter was that not only was it relatively small and light compared to other filters, but there are no moving parts whatsoever. If you were to need to replace a filter, you just replace the filter module.
The longest trip I used this filter on was a 7-day backpacking trip with one other person along Isle Royale's Minong Ridge (a lot of hiking on exposed ridges, so we definitely went through a lot of water).
I've use a Katadyn Hiker (not sure which model) on several multiday trips, pumping more than 20 liters per day. It holds up well. It is possible to break the plastic and clog the filter on any water filter, so you should have a backup plan in case it fails -- spare water filter, iodine tablets, enough fuel to boil water, etc.
If you get into some water with lots of silt (glacier silt or muddy water) it can clog up a filter. The ceramic filters seem more susceptible, but it will eventually happen with any water filter in water with lots of silt.
I prefer to carry an entire spare water filter rather than a filter cartridge. That way, I can still pump water no matter what fails on the first filter.
I would say that most filters will do just fine with 20 liters of water without the recommended maintenance.
If there was one I would consider it would be Sawyer Squeeze. The Squeeze is a hollow fiber filter which can be forced (squeezed). It is affordable, reliable and simple to use. The water is available immediately; you can even drink as you filter. I find it easier to use than a pump-style filter. You may also use it as part of a gravity system.
The Squeeze requires back-flushing using a syringe. In my experience, this is rarely required if the water is relatively clean. You may choose to bring the syringe with you although I personally would not. Another option is to mail it to yourself for long hikes (i.e. bounce box). With clear water it repeatedly worked just fine for weeks-long stretches. When it requires back-flushing you will notice reduced flow rates.
The filter is remarkably simple and does not have many moving parts. I did have problems with the O-Ring becoming misshapen, which resulted in leaks and un-usability. The problem corrected itself after a certain time. You should not tighten the bottle too hard as it may cause issues (now I know).
I also owned a MSR HyperFlow but had it failed on me in the field. I would not recommend it as it is more error-prone and more costly than the Squeeze. Ceramic filters are also reliable and field maintainable. However, I personally had bad luck with those as the cartridge broke down on a trip.
For non-filters, you could use a drops such as Aquamira. I would recommend transferring the contents of the bottles into a secondary container as the corners of the bottles tend to crack and leak. I've had it happen to me twice and I have met other hikers with the same problem. I believe Aquamira is aware of the problem but I do not know if they have corrected it. You could also keep them in the original plastic box which offers some extra protection for those sad cornered bottles.
SteriPens are great but unreliable for multi-week trips and costly (battery usage).
