In this blog post, we will explore the types and scientific principles of water purifier filters—often referred to as the “must-have technology” of the 21st century—as well as their social significance.
In our highly advanced 21st-century civilization, we take material abundance and convenience for granted. While poverty remains severe in some developing countries, it is difficult to feel a shortage of resources in advanced environments like ours. Yet, there is one essential substance that we often overlook precisely because it is so familiar to us: water. Although about 70% of the Earth’s surface is covered in water, only a mere 1% of it is fresh water suitable for human consumption. As industrialization and environmental destruction since the 18th century made it difficult to obtain clean water from nature, people developed various technologies to secure drinking water, and public water supply systems, water treatment facilities, and household water purifiers have become commonplace in cities. We rely on water management technologies—such as municipal water systems and water purifiers—just as much as we do on sending spacecraft to the moon or creating cloned animals. In particular, water purifier filters play a major role in supplying water abundantly and conveniently to homes and buildings. If it weren’t for water purifier filters, countless people would have to bear the hassle and cost of boiling and cooling water. So, what science lies behind these “must-have” water purifier filters? Let’s explore the various types of water purifier filters and their scientific principles.
Water purifier filters are components that remove harmful substances—such as bacteria, impurities, and heavy metals—from tap water as it passes through, transforming it into water suitable for human consumption. The basic principles of these filters can be broadly categorized into filtration, adsorption, and sterilization. Filtration is the process of physically removing contaminants, utilizing materials such as non-woven fabric, microfilters, hollow fiber membranes, nanofilters, and reverse osmosis (RO) membranes. Adsorption is a method that removes contaminants by binding them to a surface, such as activated carbon or silver (Ag)-treated activated carbon. Sterilization is a method of removing microorganisms from water or inhibiting their reproduction using ultraviolet (UV) lamps, iodine resin, or ozone generators. Filters are broadly classified into hollow fiber membrane and reverse osmosis types based on their filtration method; among these, the reverse osmosis method is particularly interesting from a scientific perspective, so we will examine it in detail.
To understand the principle of reverse osmosis, we must first consider the phenomenon of osmosis. To illustrate this, let’s imagine a scenario where men and women are enjoying a party in a large auditorium. Suppose the auditorium is divided by a wall with a tiny hole in the center; the hole is so small that men cannot pass through it, but women can. If the number of men and women is evenly distributed on each side, there is no problem. However, if there are relatively more women on one side and fewer on the other, the women will move through the small hole to the opposite side to restore balance. In this analogy, the people represent the entire solution, the wall represents the semipermeable membrane between the two solutions, the men represent the solute (e.g., sugar molecules), and the women represent the solvent (water). Generally, since solvent molecules are smaller than solute molecules and can pass through the pores of the semipermeable membrane, the solvent moves from the side with lower concentration (where there is relatively more solvent) to the side with higher concentration in an attempt to achieve concentration equilibrium. This is the phenomenon of osmosis.
The reverse osmosis method utilizes this osmosis phenomenon in reverse. In other words, applying external pressure to the side with the higher concentration forces the solvent to move against the natural direction of osmosis, allowing only clean water to pass through to the side with the relatively lower concentration. To use an analogy, it is like forcibly pushing women from the side with fewer women to the other side to restore balance. In this process, solutes and contaminants remain on the membrane, while only water molecules pass through, producing clean water that we can drink. Desalination, which removes salt from seawater, also operates on this principle, and reverse osmosis is highly effective for purifying groundwater or heavily contaminated water. However, reverse osmosis is costly and has the drawback of removing most of the beneficial minerals in the water during the pressurization process. For this reason, recent research on water filters has focused on developing technologies that maintain the high removal efficiency of reverse osmosis while retaining minerals.
Water purifier filters are the result of extensive human effort and research aimed at providing safe drinking water. Thanks to science and technology, we have convenient and abundant access not only to water but also to various other substances necessary for daily life. In this sense, water purifier filters can be seen as a technology that succinctly illustrates the relationship between people and science and technology in the 21st century. However, not every country around the world has water purifiers in every household like we do; there are regions where people lose their lives every day due to contaminated water. To ensure that advanced technologies, including water purifier filters, do not become a privilege enjoyed only by a select few, we must pay greater attention to the development and distribution of technology for the marginalized. It is just as important to reflect on the gifts that science and technology bestow upon society and the responsibilities they entail as it is to understand the principles behind water purifier filters.
