Potable Water

"Water, water every where, Nor any drop to drink."
- Samuel Coleridge, The Rime of the Ancient Mariner

While recent evidence indicates that there may be frozen water on Mars and the Moon, it is Earth that is unique as the Blue Planet with 71% of the surface covered in water. Sadly very little of this water is potable (meaning safe to drink).

97% of the Earth's water is salt water. NEVER drink salt water no matter how thirsty or near death. It takes twice as much water for your body to process seawater as you get from it.

Of the 3% fresh water, most of it (80%) is tied up in the polar ice caps. There is a survival lesson here too - DO NOT eat snow. Recall the Rule of Threes and how maintaining body temperature (shelter) trumps thirst. Eating snow lowers your core body temperature which can lead to hypothermia or shock.

Of the fresh, non-frozen water about 99.5 percent is not potable due to pollution or it is inaccessible (too deep, trapped in the soil, etc.). This leaves us .03 * .20 * .005 = .003% of the Earth's water available for drinking. If one liter represents all water the world, the useful-potable amount of water is just a one drop.

Say despite the odds, you have found fresh water. Is it safe? Maybe not. Giardiasis (gee-ar-die-a-sis with a soft "G") is an infection of the small intestine that is caused by a parasite that lives in fresh water. Up to 2.5 million cases of giardiasis occur each year in the US. Up to 20% of the world's population is chronically infected with Giardia lamblia.

How to Avoid Giardiasis, e-Coli and other dangers in fresh water

• Do not drink from fresh water streams or lakes without boiling or filtering the water with a pore size of less than 1mm.
• Do not use ice or drink beverages made from water that may be contaminated.
• Do not brush teeth with water that may be contaminated.
• Do not eat uncooked or unpeeled fruits or vegetables grown in conditions in which contamination with Giardia might occur.

Bottom Line
Water contamination is not just limited to mountain streams and ponds. You might get sick swallowing the water in a public swimming pool. The public tap water in many countries is unhealthy by American standards. There's a story about a tourist in Mexico was very careful to avoid tap water by drinking only Coca Cola. However he caught Montezuma's Revenge from the ice cubes in the Coke glass.