Using a UV-C pen correctly

UV-C is a short-wave part of ultraviolet light. It damages the genetic material of microorganisms – their DNA or RNA. The pathogens do not necessarily die immediately, but they can no longer reproduce and therefore cannot cause an infection. This is called inactivation.

The dose is what matters. It results from the strength of the light and the time the water is irradiated. Every device is designed for a specific volume of water; with more water the dose is not enough. Used correctly, such devices inactivate bacteria, viruses and protozoa according to the manufacturer.

UV light only works where it reaches. Particles in the water cast shadows in which pathogens are protected. Drops on the threads or the bottle rim are outside the water and are not irradiated at all. And unlike chlorine, UV leaves no residual protection: if dirt gets into the water later, it is unsafe again.

Clarity first: use only clear water. Let cloudy water settle and pour it through a coffee filter or cloth, or pre-filter it. If the water is clearly coloured or stays cloudy, choose another method such as boiling instead.

Fill exactly the volume the device is designed for into a clean wide-mouth bottle. Keep the threads and rim dry while doing so. Switch the device on, immerse it and stir or swirl as instructed until the cycle is complete. Only if the device indicates success does the water count as treated.

When drinking, it is best to use a clean cup or wipe the threads dry first. Do not top the bottle up with raw water, or everything is untreated again.

UV-C light damages eyes and skin. Never operate the lamp outside the water and do not look into it. Store the device so that children do not use it as a toy torch.

If the device shows an error or the cycle stops – for example because of a flat battery – the water counts as untreated. Cold reduces the performance of batteries. If you go into cold regions, keep batteries warm against your body, carry spares or have a second method with you, such as tablets or a stove.

UV does nothing at all against chemicals and salt. If chemical contamination is suspected, you need another source.

A UV pen suits travel where tap water is of doubtful quality but clear, and clear spring or stream water. It works quickly, does not change the taste and suits individuals and small volumes.

It is less suitable for cloudy or coloured water without clarification, for large volumes in groups, for water that is to be stored for longer, and for long trips without a way to charge. Some bottles have a UV lamp in the cap; the principle is the same, and the effective dose and duration are given by the manufacturer.

UV disinfection is an established process in public water supply. Portable devices transfer this principle to the bottle. Their effectiveness, however, depends heavily on clarity, dose and correct use – and only the manufacturer can specify these values for its device.

The sunlight method SODIS also uses UV radiation, but from the sun and over many hours. A UV-C pen works with much stronger, targeted radiation and therefore needs only a short time. Both need clear water.