The MSR Trailshot is a compact and lightweight water filter for use in the great outdoors. Photo: Bob Smith/grough

Weight: 138g
Country of manufacture: USA

Keeping hydrated in the great outdoors seems simple: take plenty of water.

But every litre of water you pack in your rucksack adds a kilogram, and it seems a little nonsensical when we choose to keep a close eye on the weight of our gear to pile on the pounds by packing lots of liquid.

One way to cut down on carrying so much water – and I can easily get through 3 litres on a mountain day walk – is to find it en route. But using streams as your source has risks. The best advice says take your water from fast-flowing streams where the water passes over rocks.

But there’s always the chance the water contains pathogens that can lead to upset stomachs or worse.

The main groups to worry about are bacteria, viruses and protozoa parasites. The last includes nasties such as giardia and cryptosporidium.

Some water may contain chemicals from agricultural processes and heavy metals from old mines. Streams in the UK often contain particulates from peat.

We would never advise taking water from lowland sources where animal faeces are common and farm chemicals could have been used, but on the hills and mountains most of us have drunk water from streams and becks with no ill effects. But the potential for picking up pathogens is always there. Boiling water at camp will kill most nasties but chemicals, metals and particulates will remain.

One solution on the trail is to use a drinks bottle that contains a filter. But that means you’re limited to using that bottle and its capacity. For those of who use a hydration reservoir in the pack with a drinking tube, refilling this from a filter bottle is a tedious and sometimes impossible task.

The Trailshot is easy to use: dangle the hose in the water and squeeze the bulb. Photo: Bob Smith/grough

MSR’s Trailshot filter is a neat solution.

It consists of a plastic bulb containing a hollow-fibre filter, with a drinking spout covered by a tethered cap.

A 40cm (16-inch) plastic hose is attached to the bottom of the bulb, and at the end of this is a housing containing a pre-filter.

Using the Trailshot is easy. Dangle the end of the tube into the stream from which you want to extract your water and squeeze the bulb a few times. The water will spurt from the spout and you can either drink straight from this or refill your bottle or hydration reservoir. The tube is long enough to drink directly from a stream in a crouching position, rather than having to lie down as is the case with some rigid filter systems.

MSR says it takes about 60 seconds to filter one litre of water, but we found that on the optimistic side unless you’ve got the hand strength of a gorilla. It took us about 1min 30secs to fill a one-litre bottle, still quite acceptable. It takes 60 squeezes of the bulb to provide a litre of water.

The whole set-up is fairly compact and will fit in many rucksack hipbelt pockets. The Trailshot comes with a broad rubber band to keep things neat, but a small waterproof pouch would be a useful addition without great extra weight or cost, as the filter retains a few drops of water after use, which will dampen a pocket.

The Trailshot scored highly in our test. Photo: Bob Smith/grough

The MSR Trailshot will remove bacteria, protozoa and particulates but not viruses, whose organisms are much smaller. It won’t deal with chemicals either.

The filter is good for 2,000 litres of water, but using it on silty or muddy water will clog the filter more quickly. MSR advises finding the cleanest water you can before filtering.

It is also advised to clean the filter by backflushing it after eight litres of filtering. This is done by half filling the bulb and shaking it for 20 seconds then removing the hose and pumping the water out of it before reconnecting the tube.

The MRS Trailshot Filter is a good piece of kit for anyone heading into the hills and countryside for any length of time – as long as your route passes a water source, of course. We were able to carry less water, sure in the knowledge we could replenish and rehydrate en route.

It’s simple in use and works well, though it’s not cheap. It takes up little space and adds less than 140g to the pack weight.

Performance: 52/60
Ease of use: 17/20
Quality: 8/10
Value for money: 6/10
Total score: 83/100

The Trailshot was supplied to grough by MSR.