What does a water filter test report contain?

Claims such as 'removes PFAS' or 'filters 99% of contaminants' sound clear, but on their own they tell you very little.

After all, which PFAS are we talking about? What was the concentration before filtration? How much was left after filtration? Was that measured only with a new filter, or also after hundreds or thousands of litres of water had passed through it?

That is why at Helder. we prefer to look at the actual test report.

What is a water filter test report?

A laboratory report describes how a water filter performed under certain test conditions.

Depending on the test, you will find things like:

• the filter element or filter system tested;

• the laboratory that carried out the test;

• the test method or standard used;

• the substances examined;

• the concentration before filtration;

• the concentration after filtration;

• the calculated reduction percentage;

• the amount of water filtered during the test;

• various measuring points during the test.

Not every report contains all of this information.

The more information is available about the test conditions, the better you can judge the result.

The key figures: influent and effluent

In laboratory reports you will often come across the terms influent and effluent.

Influent is the water before filtration.

Effluent is the water after it has passed through the filter.

Suppose a laboratory measures 1.00 µg/L of a certain substance before filtration and 0.01 µg/L after filtration.

The calculated reduction is then:

99%

That does not mean the substance has disappeared completely. The measured concentration has been reduced by 99%.

That is why we actually find the concentrations before and after filtration more informative than a big reduction percentage alone.

What does '<' mean in a test report?

In a laboratory report you might come across something like this:

<0.01 µg/L

That does not automatically mean that exactly 0.01 µg/L was measured.

A value such as <0.01 µg/L means that the concentration was below the limit stated by the laboratory. Which limit exactly is meant, for example a reporting limit or a detection limit, has to be clear from the laboratory report in question.

On the basis of such a result, the laboratory therefore cannot say exactly how much lower the actual concentration was.

That distinction is important.

<0.01 µg/L therefore does not mean the same as 0.00 µg/L.

Why is the number of litres tested so important?

Suppose two water filters show a reduction of 99% for the same substance.

For filter A, that result was measured after 10 litres had passed through the filter.

For filter B, the same reduction is still measured after 1,500 litres have been filtered.

The reduction percentage is the same, but the information the two tests give is clearly different.

That is why we don't only look at:

How much is reduced?

But also at:

After how many litres was that measured?

Some reports use several measuring points. You can then see how the filter performs over the course of the test.

Test capacity is not automatically the service life

This is an important distinction.

If a filter was examined up to 1,500 litres in a laboratory test, that does not automatically mean the filter has to be replaced after exactly 1,500 litres.

Conversely, a service life stated by the manufacturer of, say, 5,000 litres does not automatically mean that every individual reduction claim was independently tested over the whole 5,000 litres.

So there are two different questions:

1. Up to what amount of water has the reduction of this specific substance been examined?

2. What service life or replacement guideline does the manufacturer give for the filter element?

These two figures can differ from each other.

The actual service life is also influenced by the composition of the water, the concentrations of various substances and the amount of water filtered each day.

What are NSF/ANSI 42, 53 and 401?

With water filters you regularly come across references to NSF/ANSI 42, NSF/ANSI 53 and NSF/ANSI 401.

These are standards with requirements and test methods for drinking water treatment systems.

Broadly speaking:

It is important to know that a number such as NSF/ANSI 53 does not in itself tell you which substances a specific filter reduces.

You always have to look at the specific reduction claims for which the product has been tested or certified.

Certification for one claim within a standard does not automatically mean that a filter is certified for all possible claims within that standard.

Tested according to NSF/ANSI is not the same as certified

This is probably the most important distinction when reading water filter claims.

A laboratory can examine a filter according to a test method from an NSF/ANSI standard.

That does not automatically mean that the complete product is also NSF certified.

Certification assesses more than a single laboratory test. Depending on the certification, performance, materials and construction are assessed, among other things. Ongoing product certification also includes checks to verify that the product continues to meet the requirements.

That is why at Helder. we distinguish between wordings such as:

'tested according to the NSF/ANSI 401 test methodology'

and:

'certified to NSF/ANSI 401'

These two statements do not mean the same thing.

Also look at who carried out the test

A test report in PDF format is not in itself proof that a test was carried out independently.

So check who carried out the study.

Look, for example, at:

• the name of the laboratory;

• the report number;

• the test date;

• the name of the product tested;

• the test method used;

• the measurement results;

• any accreditation or certifying body.

Also check that the report actually relates to the filter you want to buy.

A test of a particular filter material alone, for example, does not automatically tell you how a complete filter element performs.

Pay attention to the test concentration

Laboratory tests are carried out under defined conditions. Certain concentrations of a substance may be deliberately added to the test water.

These concentrations can be considerably higher than the amounts normally found in Dutch tap water.

That does not make a laboratory test any less valuable. It is precisely because of the controlled conditions that performance can be examined reproducibly.

It does mean, though, that you should not translate a laboratory result one to one to the situation at home.

A filter that reduces a substance by 99% during a test does not automatically guarantee that every household, with every water composition, will achieve exactly 99%.

Look per substance, not just at the filter

A common mistake is to extend one good test result to all other substances.

Suppose a filter reduces lead by 99%.

On its own, that tells you nothing about the reduction of:

• PFAS;

• medicine residues;

• pesticides;

• fluoride;

• nitrates;

• microplastics.

Even within a single group there can be big differences.

With PFAS, for example, a filter may perform differently for PFOA than for PFBS. With medicine residues, the reduction of ibuprofen may differ from that of carbamazepine.

That is why the question:

'What percentage does this water filter filter out?'

is actually too general.

A better question is:

'How well does this filter reduce this specific substance, under which test conditions and up to which tested capacity?'

An example: 99% reduction doesn't tell you everything

Suppose you see these two claims:

On this basis you cannot simply conclude that filter A is better because 99% is higher than 98%.

Among other things, you need to know:

• was the same substance tested?

• was the starting concentration the same?

• was the same test method used?

• do the results come from independent laboratories?

• is it a single measuring point or several?

• under which conditions was it tested?

So never compare just the highest percentage.

How do we assess test reports at Helder.?

When we write on Helder. that a filter can reduce a certain substance, we try to go back to the original test data as far as possible.

In doing so, we look in particular at:

1. Which substance was actually tested?

2. Which filter element was tested?

3. Who carried out the test?

4. According to which test method?

5. What was the concentration before filtration?

6. What was measured after filtration?

7. Up to what amount of water was it tested?

8. Is it a laboratory test or a certification?

That is also the reason why in our articles on PFAS and medicine residues, for example, you see not only percentages but, wherever possible, the original measured values and test capacity too.

How do you compare two water filters fairly?

When comparing two filters, preferably use the same checklist:

When two manufacturers use different test methods, concentrations and capacities, you cannot simply set their reduction percentages directly against each other.

What does a test report not prove?

Even a good laboratory report has its limits.

A report proves how the filter tested performed under the test conditions described.

It does not automatically prove:

• that exactly the same percentage is achieved at home;

• that every substance is reduced;

• that the performance continues to apply indefinitely;

• that a filter stops working immediately after the tested capacity;

• that a tested filter is automatically certified;

• that every other filter with the same material performs the same.

It is precisely by stating these limitations clearly that a test report becomes much more useful.

Our most important tip

With a water filter, don't just read what the manufacturer says the filter removes. Look at what was actually measured.

A reduction percentage only gains meaning when you also know:

which substance + which starting concentration + which final concentration + which test method + which capacity.

That gives you much more information than a claim such as 'removes up to 99.9% of contaminants' alone.

Conclusion

A good test report helps you tell a marketing claim from a measurable result.

Don't just look at the highest reduction percentage. Check which substance was examined, how much was measured before and after filtration, up to which capacity it was tested and who carried out the study.

Pay close attention, too, to the difference between tested according to an NSF/ANSI test method and certified to an NSF/ANSI standard.

At Helder. we therefore try to use the original laboratory data as far as possible.

Not because a percentage of 99% or 99.9% sounds impressive in itself, but because only with the data around it can you judge what such a percentage really means.

FREQUENTLY ASKED QUESTIONS

What does 99% reduction mean for a water filter?
A reduction of 99% means that the measured concentration of a certain substance was reduced by 99% under the test conditions in question. It does not mean that the substance has disappeared completely from the water.

What does <0.01 µg/L mean in a test report?
This means that the concentration was below the limit stated by the laboratory. Which limit exactly is meant, for example a reporting limit or a detection limit, has to be clear from the laboratory report in question. It does not automatically mean the concentration was zero.

What is the difference between NSF/ANSI 42, 53 and 401?
NSF/ANSI 42 covers, among other things, aesthetic effects and specific reduction claims for, for example, chlorine, taste and odour. NSF/ANSI 53 contains requirements for specific health-related reduction claims. NSF/ANSI 401 focuses on specific reduction claims for so-called emerging compounds, including certain medicines, pesticides, herbicides and other chemical substances.

Is tested according to NSF/ANSI the same as NSF certified?
No. A laboratory can examine a filter according to a test method from an NSF/ANSI standard without the product automatically being NSF certified as a result. Certification includes additional assessments and, with ongoing certification, checks as well.

Why is the tested capacity important?
A reduction percentage tells you more when you know after how many litres of water the result was measured. A high reduction at the start of a test says less about performance over the service life than several measuring points over a longer test period.

Is the tested capacity the same as the service life of the filter?
Not necessarily. The tested capacity indicates up to which point a certain performance has been examined. The recommended replacement interval of a filter may be different, and the actual service life depends on water quality and use, among other things.

Can I compare the reduction percentages of two water filters directly?
Only if you also take into account the substance examined, test method, starting concentration, measuring points and tested capacity. Two percentages from different laboratory tests are therefore not always directly comparable.

Sources

• NSF: Water Filtration, Testing and Certification
• NSF: Water Filters FAQ
• NSF: Certification vs. Compliance
• NSF: NSF/ANSI 42, 53 and 401 Filtration Systems Standards