How does a LifeStraw work?


Jake Port explains the way personal filtration devices save lives by cleaning up contaminated water.


A woman uses a LifeStraw filtration at her home at Mumias in Kenya's western province.
TONY KARUMBA/AFP/Getty Images
You’re out hiking in the wilderness and feel thirsty. You open your backpack and find to your dismay that you forgot to pack extra bottles of water. It’s OK though because you did remember to bring your portable filtration straw and there’s a lake nearby that you can drink from.

There are very few natural water reservoirs in nature that do not contain some form of parasite or potentially deadly microorganism. Water is a prime breeding ground for diseases such as cholera, typhoid and dysentery and many people die each year as a result of being forced to drink from contaminated sources.

A schematic shows the filtration levels of the LifeStraw
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Enter the LifeStraw, a simple piece of technology that takes water rife with pathogens and converts it to safe drinking water within the space of a 23-centimetre tube.

The LifeStraw is but one of a wide range of products developed to offer adventurers and those living in areas with contaminated water sources the ability to carry a water purifier with them. But how do they work?

While the specific details may vary, these purifiers follow the same principles.

A straw will have the first of many filters at its tip to block larger debris and contaminants such as insects from entering the straw.

Following this the water will travel through a series of ever finer membranes and filters, leading to holes as small as 15 microns in diameter.

While this will not filter out pathogens in the form of the smallest pathogens found in contaminated water - viruses - it does remove the vast majority of microorganisms.

In order to filter everything including viruses out, an ultrafiltration filter is used in larger purifiers, which has pores as small as 0.2 microns in diameter.

Some straws will also use chemical such as iodine to back up the filtration of the membranes to chemically kill microorganisms present in the water. There is however an ongoing shift away from the use of chemicals for filtration as they can be dangerous if consumed.

By the time the water reaches your mouth through the straw it is safe to drink, but there’s still one thing wrong with it. It tastes disgusting due to either the original taste of the contaminated water or the chemicals used to kill pathogens. The answer? Activated carbon, a type of carbon that has been heated to increase its surface area, sits just before the mouth piece to remove the taste and give the water a neutral flavour.

The LifeStraw is capable of filtering nearly a litre of water in eight minutes and can filter around 1,000 litres before it needs to be replaced. That provides approximately one year’s worth of water for one person.

Now that you’ve had your drink, you blow down the straw to help clear it out and get back to your hike. Safe in the knowledge that as long as there’s a water source nearby you’ll be able to get a drink.

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Jake Port contributes to the Cosmos explainer series.
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