What happens if I drink water from a mountain stream without treating it?

It depends on whether that particular water is contaminated. You might be fine, or you could pick up parasites like Giardia or Cryptosporidium, which cause diarrhoea, stomach cramps, and other unpleasant symptoms lasting two to six weeks. The risk is there even in clear, fast-flowing streams because contamination from wildlife and livestock is invisible.

Does boiling stream water actually kill everything?

Yes, boiling is the most reliable method. Bring water to a rolling boil for at least one minute (three minutes above 2,000 metres) and it kills bacteria, viruses, and parasites including Giardia and Cryptosporidium.

Do water purification tablets work against Cryptosporidium?

It depends on the type. Chlorine and iodine tablets are largely ineffective against Cryptosporidium, but chlorine dioxide tablets can tackle it if you use the correct concentration and wait long enough—sometimes up to four hours.

Common Hazards

Can You Safely Drink from a Mountain Stream?

Clear, fast-flowing water high on a mountain can look cleaner than anything from a tap, but there may be grazing livestock, animal waste or even a dead sheep just beyond the next bend. This guide looks at how risky untreated upland water really is, whether choosing a fast-flowing source makes any difference, what filters and purification tablets actually remove, and what to do when the alternative is continuing the walk without enough water.

19 October 20268 min read