29th Oct 2018

Cryptosporidium Doesn't Care About Your Filter's 1µm Label

Cryptosporidium oocyst are typically between 3µm and 6µm in size. Common sense would suggest that a 1µm rated filter would filter out all cryptosporidium oocysts from the source – since they’re larger than the filter’s pore size – providing clean, potable water at the outlet. 

However, that unfortunately is not the case.


It is a popular misconception that the filters are rated by measuring the size of the pores, but the structure of most process filter media makes this impractical. Instead, the rating of the filter is established by challenge tests using fine particles. Typically, ISO Fine Test Dust (with a minimum particle size of 0.97µm) is passed through the filter. The target is set at a removal efficiency of 99.98% or similar.

This may appear impressive, but typically the testing is carried out at a single flow rate and under one set of test conditions. It’s more than likely that these test conditions do not line up to your everyday use conditions. 

In addition, this data may not be supported by specific cryptosporidium testing to verify the 1µm rating provides the level of risk-mitigation required for cryptosporidium retention applications.

Since the 1µm rating is applied without consideration for specific cryptosporidium retention, it cannot be relied on for this use.


Our specialised testing process takes the 1µm rating further, giving you additional cryptosporidium removal efficiency data. This information can be used to help develop a comprehensive risk assessment for your water source.

Our filters go through an additional testing process (carried out at an independent laboratory) that gives a significantly greater assurance that the filter will provide the level of protection from cryptosporidium contamination required, regardless of its use conditions. These performance tests include a group of additional cryptosporidium challenges under a variety of conditions.

The filter’s cryptosporidium removal efficiency performance is tested with both higher and lower flow rates than are typically used. This allows us to confirm that there is a safety margin in cryptosporidium removal performance in respect to the flow variations that may be found in water supply operations.

We also carry out cryptosporidium challenge testing on filters that have reached the end of their functional life (exhibiting high differential pressure)  and at higher than normal flow rate, providing the user with assurance that cryptosporidium control will be maintained up until the point when the filters are replaced with new units.

Our approach to testing our filters extensively provides confidence that our filters (when being used in real-process conditions, not just within the laboratory) are going to provide significant protection against cryptosporidium contamination. In addition, we we’re confident that our filters will continue to provide the optimal cryptosporidium removal throughout and to the end of the life of the product, until it’s replaced.

More information on Municipal Water


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