The Renaissance

The Renaissance (late 14th century to 17th century) marked the beginning of the modern era and the revival of culture, the arts, and science. During this period, a groundbreaking invention paved the way for targeted scientific research and development of water filtration systems, revolutionising the field. However, before this, Sir Francis Bacon must be mentioned. The earliest records of water filtration systems after the Dark Ages in Europe are the experiments of Sir Francis Bacon (* 22 January 1561, † 9 April 1626).

Francis Bacon’s water filtration experiments were less about purifying water itself. Rather, he aimed to desalinate seawater. He assumed that sand particles would be heavier than salt particles. Therefore, a hole could be dug on the beach, and the salt would be held back by the sand due to the upward movement of the seawater. The theory of the seawater filtration method did not work in Sir Francis Bacon’s practical experiments. Nevertheless, others later took these published experiments as a reason to increase research in water filtration technology. This included the famous Italian physician Lucas Antonius Portius (* 1639, † 1723), who illustrated a water filter in his book "Soldier’s Vade Mecum" that used three pairs of different sand filters.

A true transformation in science, especially for the development of water filters, came with the invention of the microscope, specifically the light microscope. This groundbreaking invention is the greatest milestone in the history of water filters. The Dutch spectacle makers Hans Janssen and his son Zacharias Janssen are often considered the inventors of the first compound microscope in 1590. However, only low magnifications were possible. The microscopes by the Dutchman Christiaan Huygens (* 1629, † 1695) with a two-lens eyepiece system or Robert Hooke’s microscope with a maximum 50x magnification were still not good enough. Nevertheless, Hooke was among the first to observe water droplets under the microscope to study water more thoroughly.

Water Filters in the Age of Enlightenment and the Industrial Revolution

About a century later, a Dutchman once again revolutionised microscopy and is considered the father of microscopy. The lens grinder Antoni van Leeuwenhoek (* 24 October 1632, † 27 August 1723) built microscopes with a single, perfectly ground lens that achieved 270-fold magnification. Microscopy was his lifelong passion. Among other things, Antoni van Leeuwenhoek studied the tiny life in a drop of water. He described three forms of bacteria: bacilli, cocci, and spirilla. Bacteriology, which had previously been only a mere assumption and theory, was scientifically proven.

He built around 500 microscopes, and other scientists also examined drops of water and had to realise that seemingly pure water was full of particles and life. Research in medicine and in the field of water filters was elevated to a significantly higher level. The Dutchman kept the secret of how he could make such lenses, and it was only 250 years after his death that microscopes were again able to achieve this high 270-fold magnification.

Nevertheless, the 500 microscopes built by Antoni van Leeuwenhoek revolutionised many sciences because they gave humanity insight into a microcosm of all kinds of fields. Microscopy led research and development of water filters into new dimensions.

During the Age of Enlightenment from the sixteenth to the eighteenth century, philosophers pondered the natural rights of humanity. This included the right to clean, pure water as a basic or human right. Every person deserves pure water for drinking and bathing, the philosophers of the time were already convinced. It was demanded that people in Europe should have access to pure water in every household through a city-wide water filter system.

The French scientist La Hire proposed that every French household should have a sand water filter installed to provide clean water. At that time, sand water filters were the most widespread and popular method of purifying water. It would take until the mid-19th century for the philosophers' ideas about municipal water supply to become reality.

The first records of an industrial sand water filter date back to 1804. The Scotsman John Gibb, owner of a bleaching works near Paisley, Scotland, built an experimental water filter plant and sold his surplus water to the public. His method was further developed over the next two decades by engineers from private water supply companies. In 1829, the world's first public water supply with treated water was installed by engineer James Simpson of the Chelsea Waterworks Company in London, using a so-called slow sand filter. The system, also known as a biosand water filter, uses a complex biological film that naturally grows on the sand. The sand itself has hardly any filtering properties and serves only as a substrate for the biofilm. The design of the water filter plant was copied and used throughout Great Britain over the years.

In the mid-19th century, Great Britain struggled with a cholera epidemic. Until then, the prevailing opinion was that cholera spread according to the miasma theory. Miasma, from the ancient Greek for 'pollution', was thought to be a form of bad air containing the decay of organic substances. In 1854, the British scientist John Snow discovered that cholera actually spread through contaminated water. In regions where biosand water filters purified the public water, cholera was greatly reduced. The theory was confirmed when John Snow demonstrated that many cholera deaths and the outbreak of the epidemic were linked to the water from the "Broad Street Pump", a nearby water pump contaminated by a leaking sewage pipe.

John Snow finally proved the presence of tiny cholera bacteria in the water using a microscope and used chlorine to kill the bacteria. With his publications, the population's water was now biologically purified with biosand water filter systems and chemically treated with chlorine. The pump on Broad Street was repaired, and the cholera epidemic was contained. This was the birth of municipal water filter plants and water supply companies.

In 1855, shortly after the cholera epidemic, the 'Metropolis Water Act' was passed, which was mandatory for all water supply companies in London. It was intended to set minimum standards for water quality and ensure that the metropolis was supplied with clean and healthy water. Three years later, the first chemical analyses became mandatory. These regulations became a worldwide model and led to similar municipal water laws throughout Europe. Water filter systems and treatment plants henceforth became a legally mandated necessity to ensure public health.

In the private sector, the ceramic manufacturer John Doulton set new standards with his Doulton water filter. Influenced by the industrial revolution, he shifted his ceramics business from ceramic brushes, figurines, preserving jars, and tableware to industrial applications of ceramic technology. In 1827, the Doulton water filter for home use was launched, which used various earths and clay for filtration. In 1835, Queen Victoria became concerned about the current health hazards in her drinking water and commissioned Doulton to develop a water filter for the royal household. He built a stoneware water filter operating on the gravity principle, combining the technology of a ceramic filter with the craftsmanship of a hand-crafted noble ceramic water container including a dispensing tap. This was the birth of the first jug or table water filter, which was developed not only for filtration but also in terms of design.  

Because Queen Victoria was very fond of this water filter, she allowed Doulton to put the royal coat of arms on his products. John Doulton's son Henry developed the first manganese carbon water filter in 1862, around the time the French chemist and microbiologist Louis Pasteur published his studies on the spontaneous generation of life in microbiology. This higher understanding of bacteria fueled the research and development of porous ceramics that filtered out microorganisms. The diatomaceous earth filter cartridges (microporous ceramics) could filter out over 99 percent of all bacteria. In 1906, the company Doulton brought this advanced water filter to market. It was used in hospitals, laboratories, the military, and private households worldwide. The first widely distributed commercial water filter conquered the world.

Water Filters in the Era of 20th Century Modernity

Various methods for water filters were increasingly experimented with. From the initial prevention of waterborne diseases, the field gradually expanded towards softer, less demineralised water. In 1903, water filter systems based on ion exchangers were introduced to the market for the first time. Aluminosilicates, which can reversibly absorb earth alkaline and alkali ions from a solution, were the first ion exchangers deliberately used in technology. Later, weakly acidic ion exchangers based on special carbons and weakly basic ion exchangers based on phenol resins were developed. All these types of exchangers were water filter systems with mechanically crushed and sieved granulates of specific grain sizes. With the later developed strongly basic ion exchangers, these water filter systems were also able to remove silicates from raw water.
Municipal drinking water treatment became a legal standard. With the Reich Epidemic Act of 1900 to combat dangerous infectious diseases (leprosy, cholera, typhus, yellow fever, plague and smallpox), public water was controlled for the first time in Germany. Section 35 states: "Facilities serving the general use for the supply of drinking or utility water and for the disposal of waste materials shall be continuously supervised by state officials."

In 1934, the Act on the Unification of the Health System was enacted. Section 28 of the 3rd Implementing Regulation states: "The task of the health office is to promote the procurement of sufficient and hygienically impeccable drinking water and to monitor existing drinking water supply systems." However, there were still no legally binding requirements. Only from 1959 onwards, with the Drinking Water Treatment Ordinance, was there an obligation to ensure only additives and their maximum quantities after completed treatment. This was followed by the 1980 EU Drinking Water Directive, the 1986 Drinking Water Ordinance, the 1990 revision of the Drinking Water Ordinance, the 1998 revision of the EU Drinking Water Directive, the 2001 amendment of the Drinking Water Ordinance, the 2011 first amendment of the 2001 Drinking Water Ordinance, the 2012 second amendment of the 2001 Drinking Water Ordinance, and the 2013 EURATOM Directive 2013/51 on radioactive substances in drinking water.

A major development step was the water filters based on reverse osmosis. Initially, however, there was the discovery of the osmosis membrane. The clergyman and the first French professor of experimental physics Jean-Antoine Nollet (*1700 – †1770) is considered the discoverer of osmosis and discovered the astonishing property of a semi-permeable membrane more than 250 years ago. The professor experimented in 1748 with a pig’s bladder as a separating medium between wine and water and recognised that with two different substances the membrane is only permeable to the substance with the higher chemical density. Only about 100 years later, with the production of artificial membranes that were much more reliable, could the osmosis principle be scientifically explained and understood. It took another 100 years before artificial membranes could be used industrially.

In the early 1950s, NASA faced the problem of providing astronauts with enough drinking water to enable longer stays in space. Carrying enough water was not an option due to the enormous weight. They conducted intensive research at the University of California and eventually developed an extremely efficient water filter technology based on osmosis technology. This was possible because the space agency reversed the properties of osmosis. They moved from the osmosis process to reverse osmosis.

While in normal osmosis pure water mixes with mineral-containing water as it passes through the membrane, NASA used pressure to force the mineral-containing or contaminated water to take the reverse path. With reverse osmosis, the contaminated water was pressed through the membrane and only water molecules could pass through the membrane. The result was absolutely pure drinking water. Even today, water filter systems based on reverse osmosis technology are among the most efficient.

It took nearly 10 years of development and research before space technology became series-produced water filters for industry and private households. Today, water filters with reverse osmosis technology are used in numerous areas, such as seawater desalination, municipal water treatment, wastewater disposal, private use, or in science and medicine for the production of ultrapure water. Water filters based on reverse osmosis are among the most effective and powerful filter systems in terms of the purity of the filtered water. In the USA and Asia, reverse osmosis water filters are widespread. In Europe, consumer interest is steadily growing.

Water filters in today’s 21st century

Chlorine, ozone and UV are still commonly used for disinfection in municipal water treatment. Unfortunately, water filter systems for disinfection are still predominantly used worldwide as they were a hundred years ago. However, some water utilities are increasingly relying on newer water filter technologies such as activated carbon filtration and reverse osmosis. This is likely due to growing concerns about chlorine by-products like THM (trihalomethanes), which form as a reaction between chlorine and organic substances. Since THMs have health significance, limit values have been established as sum parameters. Overall, water suppliers in the 21st century face new, major challenges. The increasing contamination of surface waters and groundwater with pharmaceutical residues, X-ray contrast agents, pesticides, herbicides, nanoplastics, uranium, nitrate and hundreds of other chemical compounds is pushing municipal water filter systems to their limits. The task of water utilities is to deliver drinking water that is safe for health, which is becoming increasingly difficult.

The market for home water filters is steadily growing. There are reports in various media and, for example, from the consumer protection agency NRW stating that water filters for home use are unnecessary because the German Drinking Water Ordinance guarantees safe water. However, water utilities cannot guarantee this, and above all, the obligation to provide flawless water applies only up to the house connection and not up to the tap inside one’s own home.

The history of water filters clearly shows how great people’s need for pure, clean water is. It is also interesting that already in ancient India, in the Sushruta Samhita — one of the most important early works of detailed studies on medicine and surgery in human history — water filters were considered necessary for good health. Throughout the history of water filters, the health aspect has been one of the leading reasons to filter water. A surprising exception to this widely known basic knowledge of human history is the European Union. After a three-year analysis by 21 scientists, the EU decided that regular water drinking does not protect against dehydration or help prevent it. As a result, advertising claims that water has a positive health effect and/or protects against dehydration are prohibited. The necessity of a private water filter for home use is a decision each person must make for themselves.

In terms of purity, modern technologies and methods can hardly be improved. Only in energy and cost efficiency can significant progress still be made, especially by municipal water suppliers. Thanks to the research and development of great pioneers, we are now able to use efficient water filters such as reverse osmosis in private households and enjoy pure water that leaves nothing to be desired. A water filter is more than just an age-old basic need. It is freedom, safety and independence that our ancestors worked hard to achieve.