Turbidity measures the cloudiness or haziness of water, caused by the presence of suspended particles such as clay, silt, organic matter, and microscopic organisms. While cloudiness itself is not directly harmful, high turbidity indicates that water quality has been compromised. This condition suggests the water treatment process may be failing or the source water is heavily polluted, violating clarity standards for safe drinking water.
The Primary Health Risk: Microbial Contamination
The primary danger posed by highly turbid water is the failure of standard disinfection processes to eliminate disease-causing microorganisms. Suspended particles create a physical barrier, shielding bacteria, viruses, and especially protozoa, from chemical disinfectants. This protective phenomenon, known as the “shielding effect,” allows pathogens to pass through the water treatment facility and into the public supply.
Protozoan parasites, such as Cryptosporidium and Giardia, are particularly concerning because their cyst or oocyst forms are highly resistant to chlorine, the most common disinfectant. When high turbidity is present, these protected organisms can survive in infectious doses, leading to outbreaks of acute gastrointestinal illness. Symptoms of these waterborne diseases often include severe diarrhea, vomiting, and abdominal cramps, which can cause dangerous dehydration, particularly in the elderly and young children.
The Hidden Danger: Chemical Adsorption
Beyond the microbial threat, high turbidity introduces a secondary health risk through the binding of chemical pollutants to the suspended solids—a process called adsorption. Fine particles, especially those composed of organic matter and certain clays, have large surface areas that act as magnets for toxic substances. These adsorbed chemicals include industrial waste products, pesticides from agricultural runoff, and heavy metals such as lead and mercury.
When turbid water is consumed, the body ingests these contaminated particles, which then release the bound chemicals into the digestive system. Unlike the acute illness caused by microbes, the ingestion of these chemical contaminants poses a risk of long-term or chronic exposure. Depending on the specific chemical, this exposure can lead to serious health issues over time, including potential neurological damage, kidney problems, or an increased risk for certain cancers.
What to Do When Water is Highly Turbid
If your water appears cloudy or an advisory has been issued, the immediate action is to use a heat-based method to ensure safety. Boiling water is an effective way to kill pathogens, but the process requires bringing the water to a full, rolling boil and maintaining it for a minimum of one minute. For those living at altitudes above 6,500 feet, the boiling time should be extended to three minutes to compensate for the lower boiling point of water.
Before boiling or filtering, it is advisable to let the solids settle out of the water, which can be done by leaving the water undisturbed for several hours. Using a clean cloth or coffee filter to strain the water after settling will remove the larger particles, which improves the effectiveness of subsequent disinfection. If using a water filter, it must be a certified system designed to remove fine particles, such as those with a pore size of one micron or less, to trap the shielded pathogens.
Home filtration systems, like those using activated carbon, may struggle when water is highly turbid, as the high particle load can quickly clog the filters, reducing their efficiency and flow rate. In these situations, bottled water should be used for drinking, cooking, and brushing teeth until local authorities confirm the water supply has returned to a safe turbidity level. Always follow the specific instructions and updates provided by your municipal water utility or public health department during a high-turbidity event.