Still water is defined as water that is not flowing or moving. While commercially bottled still water is treated and sealed for consumption, the concern focuses on environmental or long-standing water that lacks movement and circulation. The safety of drinking this type of still water is low, as the static environment creates conditions that encourage the accumulation of biological and chemical hazards. Understanding these risks is the first step in assessing whether a water source is potable.
Microbial Hazards in Stagnant Water
The absence of flow transforms still water into an ideal incubator for pathogenic microorganisms, which are the most immediate threat to human health. Stagnation allows nutrients and organic matter to settle and concentrate, creating a rich food source for microbes. The lack of oxygenation and sun exposure further aids their growth, and bacterial communities can change significantly in as little as six days of stasis.
Pathogenic bacteria thrive in these conditions, with common threats including E. coli, Salmonella, and Shigella, which can cause severe gastrointestinal distress, diarrhea, and abdominal cramps. Protozoa and parasites, such as Giardia and Cryptosporidium, are also highly prevalent in contaminated still water sources. Ingestion of these parasites can lead to giardiasis and cryptosporidiosis, characterized by watery diarrhea and nausea, and they are resistant to common disinfectants like chlorine.
Viruses, including Hepatitis A and Norovirus, are transmitted through contaminated water and can cause symptoms ranging from acute gastroenteritis to more severe systemic illness. In rare but serious cases, a free-living amoeba, Naegleria fowleri, thrives in warm, still freshwater. If water containing it is forced into the nasal passages, it can cause a nearly always fatal brain infection.
Chemical and Toxin Accumulation
Still water bodies are susceptible to the accumulation of non-living hazards that concentrate over time. Environmental runoff from agricultural lands and industrial sites introduces pollutants like pesticides, industrial solvents, and high levels of nitrates. Nitrates, originating from fertilizers and sewage, are particularly dangerous for infants under six months, as they can cause methemoglobinemia, or “blue baby syndrome,” by impairing the blood’s ability to carry oxygen.
Natural toxins also flourish in warm, still conditions, most notably those produced by cyanobacteria, commonly known as blue-green algae. These organisms form dense surface blooms and release potent toxins, such as hepatotoxins and neurotoxins, that attack the liver and nervous system. Boiling contaminated water does not inactivate these chemical toxins, making the water unsafe regardless of purification efforts.
Water standing in plumbing systems, such as in vacant buildings or old municipal pipes, can leach heavy metals like lead and copper from corroded pipes. The concentration of these metals increases exponentially with the duration of the water’s stagnation, often rising sharply within the first 20 to 24 hours. Ingestion of these heavy metals can lead to neurological damage, kidney issues, and other serious long-term health effects.
Identifying Potentially Dangerous Sources
Identifying high-risk still water sources involves recognizing both the location and the physical characteristics of the water. High-risk environmental sources include:
- Stagnant puddles and slow-moving ditches.
- Ornamental ponds.
- Any water source near agricultural fields or industrial activity.
- Water collected in uncovered cisterns or rain barrels that sits for long periods.
In a household context, water that has been sitting in pipes for more than a day, such as after returning from a trip, poses a risk due to the loss of protective chlorine residual and the potential for metal leaching.
Visual cues that indicate contamination include cloudiness, a milky or murky appearance that suggests suspended solids or microbial growth. A reddish-brown or orange tint usually signals the presence of rust or iron from corroded plumbing. Sensory indicators are also red flags. An odor like rotten eggs suggests hydrogen sulfide gas, while a musty or earthy smell points to decaying organic matter or algae blooms. A metallic or bitter taste signals the presence of dissolved metals, confirming the water is chemically compromised.
Essential Steps for Making Still Water Safe
For emergency situations involving questionable still water, thermal treatment is the most reliable method for neutralizing biological pathogens. The standard is to bring the water to a full, rolling boil for a minimum of one minute at sea level. For elevations above 6,500 feet, the boiling time should be extended to three minutes to compensate for the lower boiling temperature. This process kills or inactivates all bacteria, viruses, and protozoan cysts, though it is ineffective against chemical toxins.
Chemical disinfection, typically using unscented household bleach containing 5% to 9% sodium hypochlorite, is a viable alternative when boiling is not possible. For clear water, eight drops of bleach should be added per gallon of water, or 16 drops if the water is cloudy. After stirring the mixture, the water must stand for a minimum of 30 minutes before consumption to allow the disinfectant to work.
Filtration should be considered a pretreatment step rather than a complete purification method. Passing cloudy water through a clean cloth or coffee filter removes sediment and organic matter, which increases the effectiveness of boiling or chemical disinfection. However, most basic portable filters do not have pore sizes small enough to remove viruses or dissolved chemical contaminants, meaning a secondary disinfection step is necessary to ensure safety.