Maintaining a drinkable water supply isn’t much of a problem if you only ever

pitch up at well-maintained campsites and/or carry a supply in the van, but it’s worth having a contingency plan if you routinely stray off the beaten track.

SteriPEN makes a range of portable ultraviolet water sterilisers and its latest model is small enough to fit into a pocket.

Weighing just 74g (2.4oz), the SteriPEN Freedom is reckoned to be able to destroy 99.9% of bacteria, viruses and protozoa in 0.5 litres of water in just 48 seconds just by stirring it around — one litre can be sterilised in twice that time.

A fully charged SteriPEN is good for 40 treatments and it can even be recharged from the USB port of a laptop, making it a fuss-free addition to the van for emergencies.

The SteriPEN will be available in the US this autumn for $120 (around £75), but UK availability has yet to be finalised — keep an eye on the UK suppliers’ web page for more details.