Microscopic organisms can contaminate drinking water sources. Consuming water tainted with pathogens, such as amoebas and related protozoa, can lead to gastrointestinal illness. Filtration is a widely adopted strategy for mitigating this risk, but the effectiveness of a water filter depends entirely on the technology used. Understanding how filtration works is key to ensuring your drinking water is safe from these contaminants.
What Defines Waterborne Amoebas and Parasites
The primary waterborne threats are parasitic protozoa, such as Giardia lamblia and Cryptosporidium parvum. These organisms exist in the environment as cysts (Giardia) and oocysts (Cryptosporidium), which are their dormant, infectious stages. Their protective outer shells allow them to survive outside a host for extended periods, making them highly resilient in water sources.
The physical size of these protozoan cysts determines whether a filter can remove them. Giardia cysts are relatively large, typically measuring between 8 and 14 micrometers (µm) in diameter. Cryptosporidium oocysts are smaller, generally ranging from 4 to 6 µm. Effective physical filtration must have a pore size small enough to physically block these microscopic shells.
Why Common Filters Do Not Provide Protection
Most common household filtration devices, such as water pitchers or faucet attachments, are not designed to remove microscopic pathogens. These filters primarily use activated carbon to improve the water’s taste and odor by adsorbing contaminants like chlorine. While carbon is effective for aesthetic improvements, its pore sizes are typically too large to reliably block protozoan cysts.
The limitations of these filters relate to their performance rating, which is often nominal rather than absolute. A nominal rating indicates that the filter removes only a percentage of particles at a specified size, perhaps 80%. This means a significant number of cysts can still pass through the filter media, offering inadequate protection. For safety, a filter must provide a near-complete physical barrier, which nominal filters do not guarantee.
Proven Methods for Removing or Inactivating Amoebas
Absolute Filtration
Achieving reliable protection against waterborne protozoa requires methods that physically block the organisms. For physical removal, the filter must utilize an absolute rating, which guarantees the removal of 99.9% or more of particles larger than the stated micron size. To effectively remove Giardia and Cryptosporidium, a filter must have an absolute pore size of 1 micron or smaller. Specialized filter types, such as ceramic filters or those utilizing hollow fiber membranes, are often engineered to meet this standard.
Reverse Osmosis (RO)
Reverse Osmosis (RO) systems are also effective. They force water through an exceptionally fine semi-permeable membrane. The pore size of an RO membrane is often down to 0.0001 microns, easily rejecting protozoan cysts along with many other dissolved contaminants.
Inactivation Methods
Non-filtration methods are reliable for inactivating these organisms. Boiling water is a simple and effective technique; bringing water to a rolling boil for at least one minute will destroy all protozoan cysts. This thermal inactivation is a dependable method when other treatment options are unavailable.
Ultraviolet (UV) purification systems work by exposing the water to UV light, which damages the genetic material of organisms like Giardia and Cryptosporidium. This disruption prevents the protozoa from reproducing, effectively rendering them harmless, even though they remain physically in the water. This method is useful because Cryptosporidium is resistant to standard chemical disinfectants like chlorine.