SteriPEN – Freedom Water Purifier

You know how Doctors tell you that staying out in strong sunlight may well give you Cancer, by damaging the cells in your skin? Well, the same principle is used to destroy the workings of tiny microbes in water by the UV-generating SteriPEN.


It’s all down to DNA, which is fairly fragile stuff really and easily broken down by strong UV. In organisms as complex as you and I, our bodies can mostly deal with the damage. But if you break down the DNA in a bacteria or other microbe then they cease to be able to replicate once they hit the cosy, warm environment of your stomach, and your body can fight them off.

The SteriPEN Freedom is a traveller’s kit, comprising of the UV-generating ‘stick’, a 500ml bottle, a solar charger and a collection of wall-socket adaptors for pretty much every country.

The pen itself is the size of a couple of 9V rectangular batteries, and has a removable cap over the business end – the light bulb. The other end has a status LED and a micro-USB charging port.

The idea is that you fill your little bottle with water from any semi-clear source. It won’t work with mud-saturated water, but will happily cope with any water that lets the UV light pass through it enough to reach all the microbes. The instructions say – I love this – “water as cloudy as weak lemonade”. That makes sense to me.

Dipping a charged SteriPEN in to water activates the UV light, as well as a blue/purple glow from the stick and a flashing green LED on the other end of the pen. A cleaning cycle involves stirring the water in the bottle with the submerged  wand for 48 seconds, until the LED glows constant green. If it isn’t able to complete doing its thing, it glows red instead… fairly idiot-proof.


The Freedom comes with a natty little solar-charger, which is about the same size as an iPod, and uses a USB lead to connect to the Pen. It takes around 18 hours to charge the SteriPEN, but from that charge you get 40 purification cycles, so it would indeed work OK if you strapped it out in the sun on a prolonged trip.

The bottle is clear plastic, with a measuring scale on the side and a wide-mouth twist-off top. That’s an important point because you have to remember that, although you’re sterilising the water in the bottle, and drops left on the mouth or lid of the bottle won’t be sterilised and will still contain breedable bugs.

The bottle is, of course, BPA free, and is pretty tough so should survive the rigours of travel quite well. The hanging-loop built in to the top feels a little exposed and may be inclined to break if you dropped a full bottle on to it – but that’s a suspicion rather than something I’ve proven.steripen3

The SteriPEN Freedom comes with a little neoprene pouch for carrying and protecting the Pen and solar charger. It’s a neat design, but it’s a very tight fit and I managed to scratch the screen of my solar charger almost immediately when inserting the Pen itself.

SteriPEN has been in use for a long time around the world, and has been proven to work extremely well. It has some limits – it’s not tested on worms and eggs, and doesn’t actually filter out dirt and bugs. For the best drinking water from the natural world, I’d be tempted to team the UV-sterlisation up with a physical filtering bottle, which would leave no bits and actually remove all those dead bugs before you drank them. That would also get around the issue of the droplets on the neck of the bottle not being treated.

That said, a water-filtration bottle on its own may not kill off viruses, bacteria and Giardia, which is what the SteriPEN does well – unless you pay roughly the same amount as for this SteriPEN for a viruside filter bottle. But then again, the SteriPEN doesn’t improve the taste of whatever you put in.