Snow is frozen water, but consuming it requires careful consideration due to potential health risks. As snow falls and accumulates, it collects pollutants from the atmosphere and the ground, often requiring purification before consumption. Furthermore, the sheer cold poses an immediate physical challenge to the body. Although snow can serve as a hydration source in an emergency, it is not as simple as direct consumption.
The Physical Danger of Eating Unmelted Snow
Consuming large quantities of unmelted snow introduces a direct cold load into the digestive system, rapidly lowering the body’s core temperature. In cold conditions, this internal cooling effect increases the risk of hypothermia, a significant threat in survival scenarios. The body must expend substantial energy to melt the frozen water and warm it to body temperature. It takes approximately 117.5 food calories to melt and warm one liter of snow to the body’s core temperature.
This caloric expenditure represents a net energy loss that can exacerbate the effects of being cold, hungry, or dehydrated. When maintaining core warmth is paramount, the body’s resources should be conserved, not spent on melting ice. Therefore, always melt the snow into liquid water before drinking it, especially in cold environments or survival situations.
Identifying and Avoiding Contaminated Snow
Snow is an efficient scavenger, collecting airborne contaminants as it falls and accumulates. This atmospheric deposition means that even freshly fallen snow contains particles, including soot, dust, and microscopic pollutants. Urban snow is particularly concerning because it readily absorbs polycyclic aromatic hydrocarbons (PAHs) from car emissions, which are toxic and carcinogenic organic pollutants.
Visual cues are the first line of defense; any snow that is not pristine white is considered unsafe for consumption. Snow with yellow, pink, or gray discoloration may contain urine, algae, or concentrated dust particles and must be avoided. Location is also a factor, as snow near roads accumulates exhaust fumes, oil, gas, and road salts. Snow collected near industrial areas is likely to contain heavy metals such as mercury, zinc, and cadmium. The safest snow is freshly fallen, deep, and collected from an open area away from human activity, trees, or structures that could introduce debris.
Necessary Steps for Safe Consumption
The process of turning snow into potable water begins with careful collection. Use a clean container to scoop only the cleanest, top layer of snow, avoiding bottom layers that may contain concentrated ground contaminants. Because snow is mostly air, a large volume is needed to yield a small amount of liquid water. Once collected, the snow must be melted slowly to prevent scorching the pot, as the trapped air acts as an insulator.
To melt snow effectively, place about an inch of water in the bottom of the pot first to act as a heat conductor. Gradually add the snow to this water, stirring frequently, and continue adding snow as the existing volume melts. Once fully melted, purification is the final step to kill potential waterborne pathogens. Bringing the melted water to a rolling boil is an effective method confirmed to kill bacteria, protozoa, and viruses. The Centers for Disease Control and Prevention recommends a minimum of one minute of rolling boil, or three minutes at altitudes above 6,562 feet.