Portable water purification

Drinking water hazards

Untreated water may contain protozoa, bacteria, viruses, and larvae of higher-order parasites such as liver flukes and roundworms. Chemical pollutants like pesticides, heavy metals, and synthetic organics can also be present, along with substances affecting taste, odour, and appearance, such as turbidity from soil, colour from humic acid or algae, odours from Actinomycetes producing geosmin, and saltiness from brackish or sea water. Common metallic contaminants like copper and lead can be treated by raising pH with soda ash or lime, which precipitates them, followed by decanting or filtration; aluminium and zinc cannot be removed this way because higher pH re-dissolves their salts.

Salt removal requires reverse osmosis or distillation. Most portable treatment focuses on human pathogens and particulates. Significant pathogens in the developed world include Giardia, Cryptosporidium, Shigella, hepatitis A virus, Escherichia coli, and enterovirus. In less developed countries, risks include cholera, dysentery, and tropical enteroparasites.

Giardia lamblia and Cryptosporidium spp. cause diarrhea and are common in backcountry areas of the United States and Canada. In Hawaii and other tropical areas, Leptospira spp. are a concern. Less common in developed countries are Vibrio cholerae and Salmonella strains causing typhoid and paratyphoid. Pathogenic viruses may also be present.

Larvae of flukes, dangerous in areas frequented by sheep, deer, or cattle, can form cysts in the brain or liver if ingested, and this risk extends to plants like watercress.

Techniques

No single method handles every waterborne threat. While combining flocculation with filtration is often considered ideal, it’s hard to pull off without precisely controlling pH and settling. Using alum carelessly as a flocculant can leave too much aluminum in the water. If you need to store treated water, halogens provide ongoing protection.

Heat kills germs, though some need more heat or longer exposure. You don’t have to sterilize water—just make intestinal pathogens harmless.

Boiling won’t remove most pollutants or leave any lasting protection. The World Health Organization says bringing water to a rolling boil and letting it cool naturally is enough to inactivate harmful bacteria, viruses, and protozoa. The CDC recommends boiling for one minute, but at elevations above 6,562 feet, where water boils at a lower temperature, boil for three minutes.

All bacterial pathogens die quickly above 60°C, so the time it takes to reach a boil usually makes water safe from bacteria. Encysted protozoan pathogens may need higher heat. Pasteurization—killing enough pathogens—happens at 63°C for 30 minutes or 72°C for 15 seconds.

Some threats, like Clostridium botulinum, require temperatures above boiling (118°C), most endospores need 120°C, and prions need even more. A pressure cooker can reach those higher temperatures. Combining heat with ultraviolet light, as in the sodis method, lowers the needed temperature and time.

Did You Know?

• Human water-borne diseases usually come from other humans, so human-derived materials should be kept far from water sources.
• In some wilderness areas it is recommended that all waste be packed up and carted out to a properly designated disposal point.