When we want to preserve food, we put it in the fridge because we know that the cold will slow down the bacterias that cause spoilage. Does this principle apply to water? Does cold water contain fewer germs than warm water?
Before you drink from a cold stream, recall that fresh water contains a variety of microscopic creatures: viruses, like Hepatitis A; bacteria, like Cryptosporidium; and parasites, like Giardia. Some studies show that Cryptosporidium can be found in more than half of the lakes and streams in the U.S. Many of these germs can cause symptoms ranging from intestinal trouble to severe illness and even death.
So, is cold water safer than warm water? Not really. Germs, like Giardia, may be affected by the cold, but cold alone won't kill them. They float along in the water waiting for you to ingest them so that they can grow in your body. While cold doesn't clean water, heat does. Boiling water for five minutes is the most reliable way to kill all types of disease-causing creatures.