How to read a filtration test: the case of fluorine and nitrates

At Pure Filters, we believe that transparency starts with a good understanding of data. That's why we're publishing the full results of the tests carried out by Envirotek Laboratories (USA), an independent laboratory, on Coldstream FTO+ filters.

But reading an analysis chart can be intimidating. Here are some key elements to better interpret the results, taking two examples that are among the most difficult to treat: fluoride and nitrates.

Why are fluoride and nitrates special cases?

Unlike other contaminants such as chlorine, bacteria or pesticides, ions such as fluorine (F–) and nitrates (NO₃–) are highly soluble and difficult to capture.

They require very specific filter media (usually based on activated carbon or ion exchange resins), and their rate of reduction is highly dependent on filter wear, water pH, and overall water composition. This is why these two parameters are very good indicators to objectively judge the real quality of a filter.

What the graph shows: Evolving performance

The results of the Coldstream FTO+ tests clearly show high efficiency at the start:

• Approximately 90% reduction of fluorine in the first 500 liters,

• More than 60% on nitrates at the same stage.

But over time, this efficiency decreases, as is always the case with activated carbon filters. At the end of the cycle (around 3000 liters):

• Fluoride drops to about 4.55% reduction,

• Nitrates at about 29.63%.

This data is not a weakness, but proof of a thorough test to the maximum wear of the filter media.

The main takeaways

• The Coldstream data sheet is not misleading: it announces a maximum capacity, as all manufacturers do.

• Pure Filters specifies that this capacity mainly concerns microbiological filtration (viruses, bacteria, cysts).

• For effective protection against chemical contaminants (such as fluorine, nitrates, PFAS), we recommend replacing the filters every 6 months or 1500 liters.

• And yes, we say it clearly, unlike other brands that only publish tests on 10 L. Our chart shows you why.

Our commitment is to provide you not only with high-performance filters, but also with the tools to understand their results and limitations. Because a well-understood filter is a well-used filter.

And what about other contaminants?

Laboratory results show that Coldstream FTO+ filters are particularly consistent on many other pollutants:

• Chlorine, VOCs, HAAs: Lifetime reduction of more than 95%.

• Pesticides, herbicides, pharmaceutical residues: very good stability as well.

• Heavy metals: reduction varies depending on the metal, but is effective at the beginning of the cycle.

• Microorganisms (viruses, bacteria, cysts): exceptional performance maintained up to 3000 liters.

In summary

For the majority of contaminants, Coldstream technology provides long-lasting protection, including against microbiological agents and organic pollutants.

Highly soluble contaminants such as nitrates and fluoride in particular require special attention to the duration of the filter's use.

Are you hesitating between several brands of purifiers? Don't miss the full analysis of "The Old News": a clear, neutral and well-researched video.