Reverse osmosis: what it is, how it works and when it is actually needed. Technical guide for a waste-free choice

Summary

Reverse osmosis is often cited as the ultimate technology for water purification, capable of making almost any liquid drinkable. But is it always the right choice for the home, office, or restaurant? In this technical article, we explain the functioning of the semipermeable membrane, analyze the pros (removal of heavy metals and pollutants) and cons (demineralization, wastewater disposal, and acidity). DKR guides you through the understanding of this powerful technology, explaining when it is indispensable and when microfiltration may, in some cases, be a more logical and sustainable choice. In the vast landscape of water treatment, few technologies are as well-known and discussed as reverse osmosis. Often sold as the panacea for every water problem, it is sometimes marketed as the only way to have “pure water.” Unfortunately, the sector is affected by some retailers who adopt a non-neutral approach, seeking to sell the most expensive product instead of the most useful one; this harms the entire market and confuses the end customer, despite the efforts of trade associations such as AIAQ, Acqua Italia and Amitap to promote proper commercial ethics.

However, as we have often reiterated in our technical column, in DKR (which produces delivery systems and not filtration systems) we do not believe in universal solutions. For this reason, we strive to be neutral in the description and use of these technologies, relying on the opinion of external experts, such as Mr. Danilo Turola of the company Filtra, a company specializing in water treatment founded in 1999 with roots dating back to the 1970s, now in its third generation and part of a group capable of covering the water treatment market at 360°.

To respond, we must abandon the slogans and delve into fluid mechanics and chemistry.

What it is and how it works: physics beyond the filter

To understand reverse osmosis, we first need to understand natural osmosis. In nature, when two liquids with different salt concentrations are separated by a semipermeable membrane (which allows water to pass but not salts), water tends to move from the less concentrated solution to the more concentrated one to dilute it and balance the salinity.

Reverse osmosis reverses this natural process by applying an external force.
Through a high-pressure pump, water with a high concentration of mineral salts is forced against a synthetic membrane with extremely small pores (in the order of 0.0001 microns). The pressure overcomes the natural osmotic resistance and forces the molecules of pure H2O to pass through the other side, leaving almost all dissolved substances (salts, metals, bacteria, viruses) behind.
The result is the separation of the flow into two paths:

1. Permeate: purified water (osmosed) with a very low residual solid content.
2. Concentrate (or waste): water containing pollutants and salts that is discarded in the sewer.

The advantages: when the barrier is total

Reverse osmosis is, technically, the most advanced filtration method available at home and in industry. Its advantages are objective in critical situations:

• Removal of complex pollutants: it is extremely effective (removal rates ranging from 90% to 99%) against substances that standard activated carbon filtration struggles to retain, such as nitrates, arsenic, heavy metals (lead, mercury) and the much-feared PFAS (forever chemicals).
• Microbiological barrier: the pore size of the membrane is much smaller than that of any bacteria or virus, ensuring physical sterilisation of the permeate.
• Desalination: it is the only technology capable of making brackish or excessively high conductivity water drinkable.

Technically advanced solutions are available on the market today, such as the patented HDO and FLO reverse osmosis systems by Filtra, which are distinguished by their quick and simple maintenance, an aspect often underestimated when choosing a domestic system.

The limits and the difficulties: why “pure” does not always mean “better”

If osmosis is so powerful, why doesn’t DKR recommend it to everyone indiscriminately? Why does this technology have chemical and environmental “costs” that need to be carefully evaluated.

The paradox of demineralisation

Osmosis does not distinguish between “bad” and “good” water. It removes arsenic, but also removes calcium, magnesium, and potassium. The result is an oligomineral water, poor in nutrients and with a generally acidic pH. The World Health Organization (WHO) has repeatedly reported that drinking exclusively demineralized water for long periods can have contraindications, as it reduces the intake of micronutrients and can have an excessive diuretic effect. Furthermore, water devoid of salts leaves a “empty” or “flat” taste in the mouth. For this reason, reverse osmosis systems must have a mixing system that allows the regulation of the salinity of the permeate, or alternatively it is possible to install a remineralization system at the exit of the osmosis that only reintroduces into the water the ’good“ salts such as calcium, magnesium, and potassium.

Water wastage

To produce one liter of desalinated water, reverse osmosis systems must discard water; traditional systems discard between 2 and 4 liters, although modern technologies now allow recovery in new systems of up to 50%. In an era of water crisis and attention to sustainability, installing a system that discards 70% of the incoming water is a choice that must be justified by a real technical need (e.g., non-potable well water), but it is ethically questionable if applied to already potable and safe mains water.

Chemical aggressiveness

As explained for the softeners, water devoid of salts is chemically “hungry” and aggressive. It tends to corrode the metals of pipes and tanks if it is not properly remineralized after treatment or through the salinity regulator.

Regular maintenance of filter cartridges is a crucial element in ensuring performance over time: quality components, such as containers with a nickel-plated brass head produced by specialised companies, are now a standard adopted by the main industry operators.

The context of use: the vision of DKR

So, when do we use reverse osmosis? The answer is: when the context requires it.

• Companies like Filter, pioneers in the widespread adoption of under-sink reverse osmosis systems in Italy in the first decade of the 2000s, they contributed to making this technology accessible for both domestic and professional use.
• In the Horeca sector (café and washing): Here, osmosis is often essential, but for technical reasons, not health-related. In professional dishwashers, the osmotized water ensures sparkling glasses without limescale (which are residues of salts). In coffee machines, it allows you to precisely control the water profile for perfect extraction, although “mixing” systems are often used to reintroduce a small amount of minerals necessary for the coffee’s body.
• In areas with problematic water: If the water analysis detects the presence of abnormal nitrates (common in some agricultural areas), arsenic or dangerous levels of sodium, osmosis is the essential safety solution to make the water drinkable.
• Areas of high salinity There are areas where the public water supply does provide drinking water but with a high salinity that can sometimes exceed 500 mg/l TDS; this high salinity makes the water less pleasant to the palate; therefore, it is recommended to reduce it using a reverse osmosis system.
• Offices and homes with compliant aqueduct: theIn these cases, which represent the majority of Italian households, DKR usually recommends microfiltration or ultrafiltration. These technologies remove chlorine (which alters the taste), sediment and bacteria, but maintain the natural salt profile of the water intact. This results in good, safe water rich in minerals beneficial to health and without water waste (no waste water).

Frequently Asked Questions (FAQ)

What exactly is reverse osmosis and how does it work?

It is a process that reverses natural osmosis by applying a high-pressure pump to push water through a semipermeable membrane (0.0001 micron). This separates the purified water (permeate) from dissolved substances, such as salts, metals, bacteria, and viruses, which are discarded.

Which pollutants can reverse osmosis remove?

It is extremely effective (removing 90% to 99%) against complex pollutants that activated carbon filtration struggles to retain, including nitrates, arsenic, heavy metals (lead, mercury) and PFAS (forever chemicals). It also provides a complete microbiological barrier.

What are the limits of water treated with reverse osmosis?

The main limitation is demineralization: osmosis also removes useful minerals such as calcium and magnesium, resulting in a water low in nutrients with a pH that tends to be acidic. The World Health Organization has reported possible contraindications for long-term exclusive consumption.

Is it true that reverse osmosis causes “water waste”?

Yes. Traditional systems waste between 2 and 4 litres of water for every litre produced (although modern technologies allow for recovery rates of up to 50%). This water wastage must be justified by a genuine technical necessity.

When does DKR recommend microfiltration instead of reverse osmosis?

For the majority of users in Italy with compliant aqueducts, DKR recommends microfiltration or ultrafiltration. These remove chlorine and sediment, improving taste, but keep the natural saline profile intact, are more sustainable, and do not produce wastewater.

Analysis and personalized advice: contact the expert

Do you want to know if reverse osmosis is the right choice for your water?

At DKR, we don't sell universal solutions, but only the technology best suited to your real needs, supported by the advice of our experts.

Contact us today for a personalized consultation and discover the dispensing system that is perfect for you, without waste and without surprises.