Finnish expert warns: tap water spoils quickly during hikes

Finnish Institute for Health and Welfare researcher Ilkka Miettinen warns that tap water brought from home starts to spoil at room temperature due to microbes within three to four days. The water and microbiology expert shares practical advice on how hikers can avoid drinking contaminated water.

Summer is here and hiking season is in full swing, but many people heading out on trails don't realize that tap water brought from home can become a health hazard within just a few days. Ilkka Miettinen, a researcher at the Finnish Institute for Health specializing in water and microbiology, shares warnings that are also useful for Estonian hikers.

Why does water spoil so quickly?

According to Miettinen, the growth of microbes in water speeds up significantly at room temperature. "Microbial growth accelerates within three to four days at room temperature," he explains. If the water is in an open container or the bottle has been handled repeatedly, bacteria from the surrounding environment can enter it, further accelerating the spoilage process.

Tap water does contain a small amount of chlorine added during treatment, which inhibits microbial growth, but this protective effect quickly diminishes when stored at room temperature. The situation is particularly dangerous if a hiker fills a bottle with a multi-day supply and keeps it in a warm environment.

Practical tips for hikers

Experts recommend that hikers follow a few simple rules. First, it's a good idea to use sealed and cleaned containers that minimize the chance of bacteria getting in. Second, water should be kept as cool as possible, for example in a shaded spot or packed in a thermos. Third, it makes sense to prefer smaller water bottles that can be consumed quickly, rather than carrying a large reserve container.

For longer hikes, Miettinen recommends considering the use of water purification tablets or a compact filter that allows safe drinking from natural sources. Estonia's forests have plenty of springs, but their water should not be consumed without prior purification either.