Hydrova works by gravity: nothing to charge, nothing to pump, no power source at all. You fill the 3.8-litre bag at a freshwater source, hang it from a branch, a hook or your backpack, and gravity pushes the water through the inline filter to the tube, where it comes out safe to drink. You hang it up and get on with your day while it does the work.

The hollow-fibre membrane is designed to trap the bacteria, protozoa and parasites found in water, as well as microplastics and sediment, up to 99.99% according to lab tests. It's made for natural freshwater sources, not for salt water or for water contaminated by chemicals, fuel or heavy metals.

Streams, rivers, lakes, dams and harvested rainwater all work. For clearer water and a longer filter life, fill the bag with the cleanest water you can get to and avoid mud and thick silt. Stay away from salt water and any water you suspect contains chemicals or industrial waste.

None of the above. Hydrova runs entirely on gravity: no electricity, no batteries, no chemical tablets and no waiting for a tablet to dissolve. That's exactly what makes it dependable when load-shedding or a power cut hits.

Up to 5 678 litres of drinking water over the filter's lifetime, depending on water quality and how regularly it's maintained. Dirtier source water and skipped cleanings bring that figure down: a backflush after every use keeps the flow at its best.