There’s numerous types of water filter available. Mechanical pumps, electrical infa-red devices, water bottles with filters built in and gravity systems like this one from Platypus. The principle is a very simple one … fill a reservoir with dirty water, suspend it from a tree, your handlebars or whatever and allow the marvellous force of gravity to take effect … your dirty water simply drains into a ‘clean’ reservoir, on its way passing through a filter suspended between the two. No pumping, no batteries, no messing about … dead simple!
Both reservoirs hold a claimed 4 litres and Platypus rate the filter as good for 1.75 litres per minute, so you should be able to transform 4 litres of forestry, drainage sludge into 4 litres of lovely clean water in 2.3 minutes. The filter element has a life of 1500 litres, it’s not serviceable so once it stops doing what it’s meant to, you’ll need to buy a replacement. The whole kit, two reservoirs, filter element and hose come in a little mesh bag so you can keep everything safely together in one place … total weight for the lot on my scales is 419 g (platypus claim 272g for the same kit but with a newer type filter element). Not staggeringly light then but as I’m sure someone, somewhere once said ‘what price clean water?’.
I think the system really proves its worth in group situations, especially those when your camping spot doesn’t have a decent supply of water right next to it. In use I’ve found that once full, there’s enough water to supply 3 people overnight, that includes cooking, brewing and even a little pot washing for those who go in for that sort of thing. Both reservoirs have a zip lock type affair across the top so are very easy to fill, clean and dry after use. The zip lock itself isn’t the easiest thing to use though, there seems to be an art to closing the seal. With cold, wet hands it’s often easier not to bother attempting to close the dirty reservoir once full, as you’ve only got a 50/50 chance of success anyway. Platypus please can we have some other kind of closure, a roll top maybe or even a screw on lid would be better and would cause much less swearing in the woods and mountains!
I said earlier that the weight for the entire system was 419 g but in reality there’s no need to carry the full kit. Imagine you want some water for a brew or maybe fill your water bottle, it’s unlikely you’ll bother decanting water from the clean reservoir into your pot or bottle … you might as well just filter it straight into your container of choice, so lose the clean reservoir and stuff sack and you’ll be down to a weight of 256 g, a smaller pack size and no loss of performance.