Clean Water Starts at the Source. Why treating healthcare micropollutants before dilution deserves a bigger role in our water strategy.

When we talk about pharmaceutical residues and other micropollutants in water, the discussion quickly turns to wastewater treatment plants.

And for good reason.

Municipal wastewater treatment plants process enormous volumes of wastewater every day. Additional treatment technologies will play an important role in reducing micropollutants originating from households, healthcare, industry and many other sources.

But there is a question we should ask before investing all our efforts at the end of the wastewater chain: “If we know where a pollutant comes from, why wait until it has been diluted into millions of litres of water before trying to remove it?”

That question is particularly relevant in healthcare institutions, like hospitals.

A hospital is not one wastewater source

Hospitals are often discussed as if they were one single source of pharmaceutical pollution. They are not.

A hospital consists of highly specialised departments, each with very different patient populations, treatments and wastewater profiles. At the same time, a substantial share of hospital wastewater does not require any hospital-specific treatment at all. Water from staff toilets and changing rooms, kitchens, cooling systems, sterilisation departments and many other general functions is often comparable to ordinary domestic wastewater – or may contain even fewer relevant pharmaceutical contaminants.

Treating all of these water streams simply because they originate from a hospital therefore means treating very large volumes of water that may have little relevance to the actual healthcare-related micropollutant challenge.

The contrast with specific clinical departments can be significant. Wastewater from radiology, oncology, intensive care or nuclear medicine can contain substances at concentrations and in combinations that are hardly found elsewhere in the hospital – and sometimes hardly anywhere outside it.

This creates hotspots within the hospital itself.

At these hotspots, relatively small and identifiable wastewater streams can contain high concentrations of specific substances. Contrast media, antibiotics, cytostatics and radionuclides are examples.

That changes the logic of wastewater treatment: instead of treating all hospital water because a small part of it is highly relevant, we can identify and treat the relevant streams before they become mixed and diluted with all the others.

Dilution does not equal removal

Once these substances leave the relevant clinical department, they start to mix with much larger hospital water streams – many of which contain no specific healthcare-related contamination requiring additional treatment. After leaving the hospital, further dilution takes place in the municipal sewer system.

After leaving the hospital, they mix with municipal wastewater and become diluted further still. By the time they reach a wastewater treatment plant, the original hospital stream has become a tiny fraction of a much larger volume.

The pollutant has not disappeared. We have added water and even at low concentrations, these pollutants have environmental impact. High water volumes are undesirable because treatment infrastructure is largely determined by the volume of water that needs to be processed. At the same time, dilution works against efficient treatment: as target substances become more diluted, their selective removal generally becomes more difficult.

At the source, the opposite is true: high concentration, small volume, known origin.

Those are attractive conditions for targeted treatment.

Not every kilogram is equal

There is another problem with looking only at the total pharmaceutical load.

Hospitals represent a relatively limited share of the overall mass of pharmaceutical residues entering wastewater. But this is an average percentage derived from all pharmaceutical pollutants and hides what is happening. Different substances have very different environmental characteristics.

Persistence matters. Ecotoxicity matters. The potential development of antimicrobial resistance matters. And whether a substance can actually be removed effectively by conventional or advanced wastewater treatment matters.

One kilogram of one pharmaceutical substance cannot automatically be considered environmentally equivalent to one kilogram of another.

For some specialist medicines, hospitals account for a much larger share of wastewater emissions than the average pharmaceutical mass balance suggests – and in some cases are effectively the dominant source. Contrast media are a clear example.

So instead of asking only: “What percentage of all pharmaceutical residues comes from hospitals?”

we should also ask: “Which substances originate here, in what concentrations, what risks do they represent, and where can we remove them most effectively?”

That produces a very different water strategy.

Treat the right water, not simply more water

This distinction also matters economically.

If wastewater treatment technologies are compared purely on cost per cubic metre treated, large centralised systems have an obvious advantage. They process enormous volumes and benefit from scale. But cubic metres are not necessarily the right unit for every environmental intervention.

Imagine treating a small wastewater stream containing a high concentration of a specific pharmaceutical compound. The cost per cubic metre may appear relatively high.

But if that intervention removes most of the target substance before dilution, the relevant metrics could instead be: cost per kilogram removed, cost per environmental risk avoided, or cost per kilogram of valuable material recovered.

Viewed from that perspective, source-based treatment becomes a very different proposition.

Central treatment or source treatment? Both.

This is not an argument against advanced treatment at municipal wastewater treatment plants. The objective should not be to treat every litre of water as intensively as possible. It should be to apply the right treatment to the right water stream, at the right place.

Diffuse pharmaceutical emissions require central solutions. Medicines used at home, for example, enter thousands or millions of individual toilets. Treating every household separately would obviously make little sense.

Healthcare hotspots are different. We know where the substances are administered. We often know approximately when they are excreted. We know which patient groups receive them.

And in many cases we can identify a relatively small wastewater stream before it mixes with everything else.

Why would we deliberately give up that advantage?

The most effective future water strategy therefore does not have to choose between centralised and decentralised treatment.

It can use both.

Diffuse pollution deserves central treatment. Concentrated and identifiable hotspots deserve source-based treatment.

The patient can become part of the solution

Source treatment also introduces an interesting new perspective: the patient does not have to be a passive part of the wastewater chain.

After many treatments, a significant proportion of administered substances is excreted during the first hours after administration.

For hospitalised patients, those first urine fractions can be captured as part of normal clinical routines.

For outpatients, responsible participation could sometimes be surprisingly simple: remain in the hospital slightly longer and use a designated filter toilet before leaving.

Patients already follow instructions before and after medical procedures. They arrive fasting, temporarily stop medication, drink additional water or follow behavioural instructions after treatment.

Why could responsible use of a designated toilet not become another normal part of sustainable healthcare?

With the right workflow, patients themselves can contribute to cleaner water.

From waste removal to resource recovery

There is an additional advantage to keeping substances concentrated: what we capture today as waste could become a resource tomorrow.

Healthcare depends on valuable and sometimes strategically important raw materials.

Iodine is used extensively in X-ray contrast media. Gadolinium is used in MRI contrast agents. Nuclear medicine depends on increasingly important radionuclide production chains.

Once these materials have been diluted into municipal wastewater, meaningful recovery becomes extremely difficult.

Capture them close to the source, however, and another possibility emerges.

Filtration can concentrate target substances into manageable media. That does not automatically make recovery economically viable today, but it creates an essential first condition for future circularity: do not dilute valuable materials before trying to recover them.

Start small. Then scale.

Fortunately, source treatment does not require us to rebuild an entire hospital. That is precisely its strength.

Start with one identifiable hotspot. Measure. Learn. Standardise.

Then expand to another department, another hospital and another substance.

As implementation scales, equipment can be produced more efficiently, installation becomes standardised, filter logistics improve, monitoring becomes easier and hospitals no longer need to reinvent the business case for every individual project.

The transition can therefore be incremental rather than infrastructural. And that may be exactly what healthcare needs.

Water quality starts before the sewer

For decades, wastewater management has largely been based on collecting everything first and treating it later.

For many pollutants, that remains entirely logical. But not for all of them.

When we know where a problematic substance enters the water cycle, when it is present in high concentration, and when it can be captured from a relatively small and controlled stream, we should at least consider removing it there.

Because sometimes the smartest way to remove something from millions of litres of water is to make sure it never gets into those millions of litres in the first place.

Clean water starts at the source.