Find lightweight water filters with the features you're looking for.
How Much Lighter are Lightweight Water Filters?The big things in your backpack, the tents and sleeping bags, are obvious areas to reduce weight, but it's the smaller things, like water filters, where if you put a little work in and find the lightweight alternatives you can really reduce the weight or your backpack and practice lightweight backpacking.
There isn't a whole lot of variety in the water filter market, as a quick glance at the list of water filters will show you, but that doesn't mean there aren't heavy and light water filters. Take for example the Katadyn Combi filter, which is a pump filter that weighs a total of 580 grams, or 1.3 pounds. The MSR HyperFlow Filter, on the other hand, is a comparable pump filters that weighs only 221 grams, or .5 pounds....
- Katadyn Combi Filter - 580 grams / 1.3 pounds
- MSR HyperFlow Filter - 221 grams / .5 pounds
The Features of Light Water FiltersEven though there aren't all that many water filters on the market to choose from, there are some innovative features that separate out the lightest water filters from the rest.
- UV Water Filters - The UV Water Filter is a unique idea. The weights listed over on the list of water filters page can be deceiving because they don't include the weight of the batteries, but even with the batteries included they should still be considered ultralight water filters. When considering a UV water filter, you should also be aware that the water isn't actually filtered, just purified. Meaning that when you dip your water bottle in some stagnant water and it comes up as cloudy, the UV water filter will neutralize all the cloudy stuff in there, but you're still ingesting all that cloudy stuff. A low tech solution to this is to use a shirt or bandana as a crude sort of filter. Not perfect, but it will do a decent job.
- Chemical Water Treatment - Why take the filter at all? Using chemicals to kill everything in the bottle is an alternative water treatment method popular with lightweight backpacking enthusiasts, mainly because the chemicals weigh almost nothing. You can take a look at the MSR MIOX water purifier, or check out some of the other chemical treatment options available. Keep in mind though that like UV Filters, you're not actually filtering your water, so watch out for the cloudy stuff.
The Drawbacks of Light Water FiltersWith most ultralight water filters, the most common problem you're going to run in to is the amount of water that can be pumped before the filter needs to be replaced. As you can see on the list of water filters, there are some that can be used almost indefinitely without needing to replace anything, and this is because you can clean them yourself. With UV water filters, the most pressing problem is going to be the battery. For a short trip you probably wouldn't have to carry extra batteries, but on a longer trip that could be a problem that you run in to, and it's no fun carrying extra batteries.
And as mentioned above, UV Filters and chemical water treatments don't actually filter the water, and while this is an easy problem to fix, it's another hassle that you might not be interested in dealing with. In the end though, there's no perfect water filtering system, they all have their drawbacks.