Purewell Personal Water Filter Straw: features, specs and who it suits

The Purewell personal water filter is a straw-style filter that you drink through directly or fit to a bottle. It is a lightweight piece of kit for camping, hiking and backpacking, and for emergency kits where clean drinking water may be hard to get. Here is what its stated specs mean.

How a filter straw works

A straw filter pushes water, as you suck on it, through a membrane with very small pores. Particles and organisms larger than the pores are held back, and the rest passes through. Nothing needs charging or pumping, and there are no parts to assemble beyond the straw itself.

Purewell describes two ways to use it: get down to a stream or lake and drink straight from the source, or fill a bottle and insert the filter to sip from it.

The 0.01-micron membrane

Purewell lists an ultrafiltration hollow fibre membrane with 0.01-micron filtration accuracy. A micron is a thousandth of a millimetre, so ultrafiltration is a very fine level. The brand says the filter removes up to 99.9999 per cent of tiny material, sand and sediment. Ultrafiltration membranes generally remove bacteria and many protozoa, but typically do not remove dissolved chemicals or salt. For what the filter is and is not designed to handle, rely on the manufacturer's documentation.

The four stages

According to the brand, the water passes through four stages:

1. A hollow fibre UF membrane.
2. PP cotton (a polypropylene pre-filter that catches coarse particles).
3. Coconut shell activated carbon, which generally helps with taste and odour.
4. A second PP cotton stage.

Purewell says the plastics are food grade and BPA-free.

Lifespan

The listing says the filter can supply up to 1,500 litres of drinking water. As with all filters, the real life depends on how cloudy the source water is, so follow the care and replacement guidance in the manual. Dirty water tends to clog a membrane sooner.

Using it in the field

The listing gives no dimensions, so check the product's size and weight against your pack. In general, a straw filter is easy to carry, but you can only drink from it as you go, rather than filtering large volumes for camp. Many hikers carry a second method for group use or for water they are unsure about.

Who it suits

It suits day hikers, campers and backpackers who want a light personal filter, as well as people building a basic emergency kit. It is meant for one person drinking, not for treating water for a group.

What to check before you buy

• Your water source: know what you might encounter, and whether chemical contamination is a possibility, since filters like this are not built for that.
• Cold weather: filters with hollow fibre membranes generally should not be allowed to freeze, so check the manual.
• Care: follow the instructions on cleaning, flushing and storing the straw.
• Use limits: confirm the maker's stated use and lifetime for the model you receive.
• Backup: consider a second way of treating water on longer trips.

The short version

• A personal straw-style water filter from Purewell.
• 0.01-micron ultrafiltration membrane, with four stages including activated carbon.
• Rated by the brand at up to 1,500 litres.
• Drink directly from a source or through a bottle.
• Follow the manual and local guidance for water treatment.

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