Snow can be used as a source of drinking water, a necessity that often arises in winter survival or emergency situations. While the abundance of snow suggests an accessible water source, converting it into safe, potable liquid requires specific knowledge and technique. The seemingly clean nature of fresh snow can be deceptive, and consuming it without proper preparation can lead to health risks. The process requires understanding contaminants, melting mechanics, and purification steps to ensure the water is safe.
Contaminants and Safety Risks
A common misconception is that fresh snow is pristine and safe to consume directly. However, snow is not pure distilled water; it acts as an atmospheric scrubber, collecting particles and substances as it falls. Even in remote areas, microbial life is present, as bacteria and other microorganisms are dispersed by wind. These microbes, while dormant in the frozen state, become active and potentially pathogenic once the snow is melted.
Environmental pollutants pose a significant concern, especially near industrial or urbanized areas. Snowflakes pick up black carbon, or soot, from vehicle exhaust and combustion sources, along with other airborne chemicals. Heavy metals and pesticide residues can also accumulate in the snowpack, particularly if the snow is not freshly fallen. Even seemingly white snow can contain invisible hazards that require purification before drinking.
Proper Techniques for Melting and Purification
Safely converting snow to water begins with selecting the cleanest source possible, avoiding snow that is discolored or near roads, buildings, or animal tracks. The melting process must be managed carefully to avoid scorching, which wastes fuel. Since snow is mostly air and acts as an insulator, placing a large quantity directly over heat can burn the bottom of the container before the snow melts.
The most efficient method is to begin with about an inch of liquid water in the pot to help transfer heat. If no water is available, start with a small handful of snow and allow it to melt gently, stirring constantly. Add snow incrementally, a handful at a time, allowing each addition to melt into the existing water before adding more. Keeping a lid on the pot helps trap heat and steam, improving melting efficiency and conserving fuel.
After the snow is melted, purification is necessary to eliminate microbial threats. The most reliable method is bringing the water to a rolling boil, which effectively kills bacteria, viruses, and protozoa. Maintain a vigorous, rolling boil for at least one minute, or up to three minutes at very high altitudes where water boils at a lower temperature. As an alternative, chemical purification tablets containing iodine or chlorine can be used if fuel is scarce, following instructions for the correct water-to-tablet ratio and contact time.
Understanding Snow Volume and Water Quality
A practical challenge is the sheer volume of snow needed to produce usable liquid water. Snow is primarily trapped air, giving it a high volume-to-weight ratio. The typical snow-to-water ratio is approximately 10-to-1, meaning 10 inches of average snow melts down to one inch of liquid water. This ratio can vary widely, from 5-to-1 for heavy, wet snow, to 20-to-1 or more for dry powder.
This high ratio directly impacts energy expenditure, requiring substantial fuel to melt enough snow for hydration. The resulting water often tastes bland or “flat” because melting and boiling removes dissolved gasses and minerals. While this demineralized water is safe to drink, the lack of minerals can be off-putting. Adding an electrolyte tablet or flavoring can improve the taste and help replenish trace minerals.