There are several popular modes of water treatment and purification currently available. In fact, the market has become so overwhelmed with water treatment products that it can be difficult for a consumer to know which option best suits his or her needs. Each mode of water treatment has its strengths and weaknesses, and each has particular situations for which it is ideal.
In the following paragraphs, you can read a brief overview of three common methods of water purification: reverse osmosis, distillation, and water filtration.
Included in this overview is an explanation of the process each water treatment method uses, as well as a listing of the contaminants that each method will remove from drinking water. We hope that as you peruse this overview, you will become more educated about water treatment alternatives and will be able to choose the most appropriate method for your specific needs.
Reverse osmosis was developed as a water treatment method more than 40 years ago. The process first arose as a technique of desalinating seawater. Once the method’s decontaminating capabilities were recognized, reverse osmosis systems began to be commercially produced for home water purification purposes. Such systems were installed in homes as early as the 1970s. Reverse osmosis systems seemed a viable option to the more costly and energy-wasteful distillation units.
The reverse osmosis process depends upon a semi-permeable membrane through which pressurized water is forced. Reverse osmosis, simply stated, is the opposite of the natural osmosis process of water. Osmosis is the name for the tendency of water to migrate from a weaker saline solution to a stronger saline solution, gradually equalizing the saline composition of each solution when a semi-permeable membrane separates the two solutions. In reverse osmosis, water is forced to move from a stronger saline solution to a weaker solution, again through a semi-permeable membrane. Because molecules of salt are physically larger than water molecules, the membrane blocks the passage of salt particles. The end result is desalinated water on one side of the membrane and a highly concentrated, saline solution of water on the other side. In addition to salt particles, this process will remove a select number of drinking water contaminants, depending upon the physical size of the contaminants. For this reason, reverse osmosis has been touted as an effective drinking water purification method.
Pros and Cons:
Reverse osmosis is a valuable water purification process when mineral-free water is the desired end product. Most mineral constituents of water are physically larger than water molecules. Thus, they are trapped by the semi-permeable membrane and removed from drinking water when filtered through a reverse osmosis system. Such minerals include salt, lead, manganese, iron, and calcium. Reverse osmosis will also remove some chemical components of drinking water, including the dangerous municipal additive fluoride.
Although reverse osmosis does extract several contaminants from drinking water, its removal capabilities are not ideally suited to the challenges of the municipally treated water that the overwhelming majority of people receive. Municipal water contains such contaminants as chlorine and volatile organic chemicals (VOCs). Because these contaminants are physically smaller in size than water, the semi-permeable membrane cannot prohibit them from passing through with the water. Thus, they remain in drinking water.
Reverse osmosis, also, by removing alkaline mineral constituents of water, produces acidic water. Acidic water can be dangerous to the body system, causing calcium and other essential minerals to be stripped from bones and teeth in order to neutralize its acidity. Trace elements of minerals were intended to be in water; their removal leaves tasteless, unhealthy drinking water.
Reverse osmosis, although it is less wasteful than distillation, is still an incredibly inefficient process. On average, the reverse osmosis process wastes three gallons of water for every one gallon of purified water it produces.
The process of distillation has been known and used for millennia. Although it has primarily been employed as a method of producing alcoholic beverages like whisky and vodka, distillation also works as a technique of water purification. In the 1970s, distillation was a popular method of home water purification, but its use is now largely confined to science laboratories or printing industries.
The distillation process utilizes a heat source to vaporize water. The object of distillation is to separate pure water molecules from contaminants with a higher boiling point than water. In the distillation process, water is first heated until it reaches its boiling point and begins to evaporate. The temperature is then kept at a constant. The stable temperature ensures continued water vaporization, but prohibits drinking water contaminants with a higher boiling point from evaporating. Next, the evaporated water is captured and guided through a system of tubes to another container. Finally, removed from the heat source, the steam condenses back into its original liquid form. Contaminants having a higher boiling point than water remain in the original container. This process removes most minerals, most bacteria and viruses, and any chemicals that have a higher boiling point than water from drinking water. For this reason, distillation is sometimes valued as a method of obtaining pure drinking water.
Pros and Cons:
Distillation, similarly to reverse osmosis, provides mineral-free water to be used in science laboratories or for printing purposes, as both functions require mineral-free water. It removes heavy metal materials like lead, arsenic, and mercury from water and hardening agents like calcium and phosphorous. Distillation is often used as the preferred water purification method in developing nations, or areas where the risk of waterborne disease is high, due to its unique capabilities to remove bacteria and viruses from drinking water.
Distillation has several qualities that make it undesirable for the purification of municipally treated water, especially when compared to the decontamination capacities of water filters. Although distillation processes remove mineral and bacterial drinking water contaminants, they do not remove chlorine, chlorine byproducts, or VOCs. These chemicals, which have a lower boiling point than water, are the major contaminants of municipally treated water. Most dangerous metals and bacteria are removed from water prior to its arrival at a home’s plumbing system. Thus, a distillation system, targeted at the removal of these contaminants, is unnecessary and irrelevant for most people.
Distillation, like reverse osmosis, provides mineral-free water that can be quite dangerous to the body’s system when ingested, due to its acidity. Acidic drinking water strips bones and teeth of valuable and essential mineral constituents.
Furthermore, distillation is an incredibly wasteful process. Typically, 80% of the water is discarded with the contaminants, leaving only one gallon of purified water for every five gallons treated.
Water filters have a long history as a method of water purification, beginning as early as 2000 b.c.e. in ancient Egypt. Filtration has evolved from the simple Hippocratic sleeve of ancient Greece, made from cloth, to the complicated solid block carbon and multimedia water filters currently on the market. Water filtration is now the premier method of water purification, removing more water contaminants, more efficiently, than any other technique.
The filtration process involves some type of filter media, over which water flows. This filter media blocks passage of contaminants through physical obstruction, chemical adsorption, or a combination of both processes. Material construction of the filter media varies widely, but the most effective medias are made from carbon or a combination of carbon with other elements. Modern filtration technology allows water filters to remove more and more contaminants through the chemical process of adsorption. In the adsorption process, contaminants are encouraged to break their bond with water molecules and chemically adhere to the filter media. Generally, water goes through several stages of filtration to ensure that each filter media will remove the ultimate number of contaminants. Water normally passes through a water filter at a relatively low speed, in order to ensure adequate contact time with the filter media. Once the water has passed through the required stages of filtration, it emerges as pure drinking water, free from contamination.
Pros and Cons:
Unlike reverse osmosis and distillation process, water filters are not limited in the type or size of contaminants they can remove. Thus, water filters are able to remove far more contaminants than any other purification method. Also, because they use the chemical adsorption process, water filters can selectively retain healthy trace minerals in drinking water.
Filtration is the only one of the three water purification methods that is capable of removing chlorine, chlorine byproducts, and VOCs from drinking water. Chlorine and VOCs are the most dangerous and threatening contaminants of municipally treated drinking water. Besides the removal of these dangerous chemicals, water filters also extract from drinking water the chlorine-resistant protozoa giardia and cryptosporidium. These protozoa have plagued the water treatment industry for several decades and have caused a number of epidemics of severe gastrointestinal disease, contracted through drinking contaminated water.
Water filters, because they do not require the costly energy sources of reverse osmosis and distillation, provide a source of relatively inexpensive, purified water. Also, water filters waste very little water, as compared to reverse osmosis and distillation systems.
Depending upon the type of filter used, water filtration may be a less than ideal form of water purification. For example, granular filters do not utilize the chemical adsorption process, allowing several contaminants to pass through the filter media. Likewise, rapid water filters allot water inadequate contact time with the filter media, limiting the number of contaminants that may be removed. Solid block carbon filters solve both of these problems by using both adsorptive and slow filtration processes. Solid block carbon filters are absolutely the best and most effective water filters available.