When people hear the word filtration, they often imagine one simple goal:

Remove as much as possible.

It sounds logical.

If something is in the water, why not remove it?

However, water treatment is more complicated than that. Water naturally contains minerals and other dissolved substances. Some are undesirable at certain concentrations, while others are simply part of the water’s natural composition.

That is why the goal of good filtration is usually not to remove everything.

Instead, it is to remove or reduce the substances that actually need to be controlled, while keeping the rest of the water suitable for its intended use.

Is purer water always better?

Not necessarily.

The word “pure” can mean different things depending on the context.

Water used in a laboratory may need extremely low concentrations of dissolved substances.

Drinking water has different requirements.

Process water for a manufacturing application may need a completely different composition again.

Therefore, there is no universal definition of “the best water.”

The right treatment depends on:

the intended use
the source water
the substances present
the required quality
the treatment technology

In other words:

Good filtration starts with a water-quality target, not with the smallest possible number of dissolved substances.

Natural drinking water contains dissolved minerals

Water naturally picks up substances as it moves through soil and rock.

Calcium and magnesium are common examples.

They contribute to water hardness and can influence taste and scaling.

These minerals are not automatically contaminants that need to be removed.

The WHO recognises calcium and magnesium as naturally occurring constituents of drinking water and notes that they contribute to its mineral composition. [WHO, Nutrients in Drinking Water, https://www.who.int/publications/i/item/9789241595827] (who.int)

So a filter that removes calcium and magnesium is not necessarily producing “better” water.

It is producing different water.

Whether that is useful depends on the application.

Reverse osmosis is a good example

Reverse osmosis can remove a very broad range of dissolved substances.

The membrane acts as a barrier that allows water molecules to pass while rejecting many dissolved salts and other substances.

That makes RO highly useful when very low concentrations of dissolved solids are required.

However, RO also produces a relatively low-mineral permeate.

Depending on the application, additional treatment may therefore be needed to adjust the final water composition.

The U.S. EPA identifies reverse osmosis as a technology capable of removing many dissolved inorganic and organic contaminants, while also noting the importance of concentrate management. [U.S. EPA, Overview of Drinking Water Treatment Technologies, https://www.epa.gov/sdwa/overview-drinking-water-treatment-technologies] (epa.gov)

Why does this matter for drinking water?

Drinking water is not simply H₂O.

It naturally contains dissolved minerals.

Those minerals can influence:

taste
hardness
scaling
alkalinity
overall water chemistry

Removing some of them can be useful.

Removing all of them is not automatically an advantage.

This is why drinking-water treatment often focuses on meeting health-based and operational targets rather than producing chemically pure water. [WHO, Guidelines for Drinking-water Quality, https://www.who.int/publications/i/item/9789240045064] (who.int)

“Zero” is not always the best target

A common marketing approach is to present zero as the ultimate goal.

Zero minerals.

Zero dissolved solids.

Zero contaminants.

But a target of zero only makes sense if zero is actually required.

For some substances, a very low concentration may be appropriate because of health concerns.

For others, complete removal may offer little practical benefit.

The right question is therefore:

What concentration is appropriate for this substance and this application?

That is a much more useful question than simply asking how close a filter can get to zero.

Selective filtration can make more sense

A selective filter aims to target specific substances.

Instead of removing everything indiscriminately, it can focus on the compounds that matter.

This can have several advantages.

The filter may:

preserve desirable minerals
reduce unnecessary treatment
use less energy
extend media lifetime
simplify downstream treatment

The exact benefit depends on the technology and application.

Nevertheless, the principle is simple:

Targeted treatment can be more efficient than maximum removal.

This is where adsorption becomes interesting

Adsorption works through interactions between a substance and a surface.

The filter medium does not need to remove every dissolved component.

Instead, its surface can interact more strongly with certain target substances.

Activated carbon is a familiar example.

It can adsorb many organic compounds, although performance depends on the specific contaminant and water chemistry.

Other adsorptive materials can be designed around different target substances.

Therefore, adsorption can support a more selective treatment strategy.

Water chemistry still matters

A selective filter does not operate in isolation.

The surrounding water can influence how strongly a target contaminant interacts with the filter medium.

Important factors can include:

pH
dissolved minerals
natural organic matter
contaminant concentration
temperature
flow rate
contact time

For activated carbon, the EPA identifies water chemistry, organic matter, flow rate and contact time as important factors affecting treatment performance. [U.S. EPA, Overview of Drinking Water Treatment Technologies, https://www.epa.gov/sdwa/overview-drinking-water-treatment-technologies] (epa.gov)

So even a highly selective filter needs to be matched to the actual water.

What if the water is already low in minerals?

This is another reason blanket filtration can be inefficient.

Imagine source water that already has relatively low concentrations of certain dissolved substances.

A highly aggressive treatment system may remove them anyway.

The result may then require additional adjustment.

In contrast, a treatment system designed around the actual water composition could focus only on the substances that require reduction.

That approach can reduce unnecessary treatment.

Filtration should match the problem

Consider three different examples.

Drinking water

The objective may be to reduce specific contaminants while maintaining suitable taste and mineral composition.

Laboratory water

Very low concentrations of dissolved substances may be essential because even small residues can interfere with analytical results.

Industrial process water

The required composition depends entirely on the production process.

Each application needs a different treatment target.

Therefore, asking “Which filter is strongest?” is usually the wrong starting point.

Ask instead:

“What does the water need to achieve?”

A stronger filter is not necessarily a better filter

Imagine two filtration systems.

System A removes almost everything.

System B selectively removes the target contaminants while preserving most of the existing mineral composition.

If both systems meet the required water-quality target, System B may be preferable.

Why?

Because unnecessary removal can require additional treatment, energy or materials.

The most technically sophisticated system is not automatically the most appropriate one.

Treatment should be proportional to the problem.

Over-treatment can increase resource use

Every treatment stage requires resources.

Depending on the technology, that can include:

energy
water
filter media
chemicals
maintenance
replacement parts

Reverse osmosis, for example, can produce a concentrate stream. Ion-exchange systems can require regeneration. Activated carbon eventually needs replacement or regeneration.

Consequently, removing substances that do not need to be removed can increase the overall resource demand without improving the actual treatment outcome.

What about TDS?

TDS, or total dissolved solids, is often used as a quick indicator of dissolved material in water.

A lower TDS value can sound better.

But TDS does not tell you which substances are present.

Two samples can have similar TDS values while having very different chemical compositions.

Conversely, water with a higher TDS value is not automatically unsafe.

The WHO treats TDS as one water-quality parameter rather than a complete measure of drinking-water safety. [WHO, Total Dissolved Solids in Drinking-water, https://www.who.int/teams/environment-climate-change-and-health/water-sanitation-and-health/chemical-hazards-in-drinking-water/total-dissolved-solids] (who.int)

So:

Lower TDS ≠ automatically better water.

What about minerals and taste?

Mineral content can influence how water tastes.

Calcium, magnesium, bicarbonate and other dissolved substances contribute to the overall sensory profile.

If a treatment system removes much of this mineral content, the taste can change.

That does not automatically mean the water has become better or worse.

It means the water chemistry has changed.

Taste is therefore one consideration when defining the desired final water composition.

More treatment can also mean more maintenance

Highly intensive treatment systems can require additional components.

For example, an RO system may need:

pretreatment
membrane cleaning
membrane replacement
concentrate management

A multi-stage system may require several cartridges.

Each additional stage adds another component that needs monitoring and maintenance.

Therefore, the simplest system that reliably achieves the required water quality can often be the most practical.

The goal is controlled treatment

A good filtration system should answer three questions:

What needs to be removed?

Identify the target contaminants.

How much needs to be removed?

Define the required concentration or performance target.

What should remain?

Preserve substances that are useful or harmless for the intended application.

This creates a much more precise treatment strategy.

“Remove everything” is especially problematic with complex water

Natural water contains many substances.

Some are contaminants.

Others are simply part of its chemical composition.

A treatment system that removes everything cannot distinguish between the two unless it has been designed to do so.

Selective treatment therefore becomes increasingly valuable as water chemistry becomes more complex.

What does this mean for PFAS?

PFAS provide a good example of targeted treatment.

If PFAS are the concern, the treatment objective is to reduce the relevant PFAS compounds to the required level.

There is no reason to assume that every mineral in the water must also be removed.

A treatment strategy can therefore focus on the target contaminant while preserving other parts of the water composition.

The appropriate technology depends on the specific PFAS, concentration and water chemistry.

The same principle applies to other contaminants

The idea is not limited to PFAS.

Different substances require different treatment mechanisms.

For example:

particles may require physical filtration
certain metals may respond to ion exchange or adsorption
organic compounds may be treated with activated carbon
dissolved salts can require membrane processes
microorganisms require disinfection or appropriate microbiological barriers

There is no single treatment mechanism that is optimal for every contaminant.

That is why water analysis should come before filter selection.

The Klar2O perspective

Klar2O’s Smart Surface Technology uses biochemically coated silica beads designed to interact with target contaminants through adsorption rather than relying solely on physical pore size. [Klar2O, About Us, https://klar2o.com/about-us]

This reflects a broader shift in filtration:

from maximum removal toward more targeted interactions.

Instead of treating every dissolved substance as something that needs to be eliminated, the filter can be designed around specific interactions with target contaminants.

That approach can help preserve more of the original water chemistry while addressing the substances that actually require treatment.

Can a filter be too good?

Yes, if “too good” means removing substances that did not need to be removed in the first place.

The best filter is not necessarily the one that produces the lowest possible TDS.

Nor is it necessarily the one with the highest removal percentage.

The better question is whether the system achieves the right water quality with an appropriate use of resources.

That means considering:

target contaminants
required concentrations
water chemistry
treatment technology
energy use
water recovery
maintenance
filter lifetime

The bottom line

Water treatment is not a competition to see how close we can get to zero.

For some applications, extremely pure water is exactly what is needed.

For others, removing everything would simply create additional treatment requirements without providing a meaningful benefit.

The goal is not maximum removal.

The goal is appropriate removal.

A well-designed filtration system removes what needs to be removed, preserves what can remain, and does so with as little unnecessary resource use as possible.

In modern water treatment, selectivity can be more valuable than brute-force purification.

Verschlagwortet Adsorption, Drinking Water, Reverse Osmosis, Selective Filtration, Sustainable Filtration, TDS, Water Chemistry, Water Filtration, Water Quality, Water Treatment

Can a Filter Be Too Good? Why Removing Everything Is Not Always the Goal