Why is Water Treatment Important?
Clean water is a basic necessity for humans. While the human population grows, the demand for water grows as well. Since water is a finite resource, used water must be treated to continuously serve end-uses. This is where the importance of water treatment systems comes in.
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Water treatment helps in removing contaminants and hazardous substances from the water, making it clean and safe to drink and be used for other purposes. Unfortunately, almost 2 billion people in the world use either untreated drinking water or get water from unsafe or contaminated sources. Having systems in place to improve water quality helps intervene in these situations and prevent unsafe water-caused incidents, such as water-borne diseases and fatalities.
On the other hand, water treatment is also helpful in ensuring that water gets reintroduced back to nature’s cycle. One of the end-uses of this process is to safely return water to environmental sources like rivers, lakes, and oceans. Of course, water treatment facilities must ensure that water is free from harmful substances before doing so to avoid contamination and other environmentally disastrous issues such as water pollution.
The United States Environmental Protection Agency (EPA) sets forth guidelines for organizations for protecting the environment and human health. One of the violations that an EPA report helps keep in check regarding an organization’s compliance with environmental safety is the illegal discharge of pollutants that could end up in bodies of water. An example of this is dumping untreated and contaminated wastewater directly into the sewer system, which is a violation of the Clean Water Act.
Process
In most cases, water treatment plants are responsible for collecting, treating, and distributing supplies of water, whether for residential, commercial, or industrial uses. Globally, these facilities may follow slightly different processes in their water treatment systems. However, their methods are all based on similar stages depending on the end use they aim to achieve.
What are the 5 steps of water treatment?
According to the Centers for Disease Control and Prevention (CDC), the overall water treatment process, especially for public water systems, consists of 5 major steps:
1. Coagulation
The first step of getting water treated is through coagulation. This involves adding chemicals with a positive charge to the water which should neutralize the negative charge of dirt and other dissolved substances. Such chemicals include iron and specific types of salt.
2. Flocculation
This step refers to the process of gently mixing the water to create larger, heavier particles known as flocs. In most cases, additional chemicals are being added to the water to allow the flocs to form easily.
3. Sedimentation
Once flocs form, they settle to the bottom of the water because they are heavier. This is called sedimentation in water treatment, which is one of the processes that water treatment plants use in separating the solids, such as flocs, from the water before going to the next step.
4. Filtration
The water again goes through another process of solids separation through filtration. The separated, clear water on top now passes through filters with various pore sizes, made from different materials such as sand and gravel. Ultimately, these filters are in place to help remove dissolved particles and unwanted substances from the water.
5. Disinfection
During this step, any remaining parasites, bacteria, and viruses must be eliminated. This can be done by adding one or more chemical disinfectants to water such as chlorine or chlorine dioxide. Why do water treatment plants do this? It’s to keep water safe when traveling from the water treatment plant to homes and businesses because chemical disinfectants help eliminate the remaining unwanted microorganisms before the water reaches the intended end-use.
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Different Types and Uses
Generally, water treatment systems differ in serving specific end-uses. The 3 most common types are the following:
Household Water Treatment
According to the National Sanitation Foundation (NSF), the general kinds of systems that are used as water treatment solutions include the following:
- Point-of-use (POU) systems – water pitchers, faucet filters, and reverse osmosis (RO) systems, etc.
- Whole-house/point-of-entry (POE) systems – municipal systems, pressurized storage tanks, UV microbiological systems, water softeners, etc.
Also, home water treatment systems either use advanced water treatment or conventional septic tank systems to treat water from households.
Industrial Water Treatment
This process refers to the treatment that is performed pre- and post-industrial use. Since businesses from various industries use water differently, water treatment processes can be done before or after performing business activities to serve the intended use of water. For example, water treatment in the Food and Beverage sector under the Hospitality industry is crucial for ingredient water used in processing food. On the other hand, manufacturing plants in the Automotive industry need to reuse or dispose of wastewater, and water treatment can help in that process.
Wastewater Treatment
Wastewater refers to any used or polluted form of water, generated after different types of uses and applications. Its sources include rainwater runoff and human activities. Wastewater treatment is key to removing any contaminants and being able to convert the quality of wastewater and turn it into an effluent that can be safe to return to the water cycle.
Common Problems in Water Treatment
Communities, states, and countries know the importance of safe water for public use, but major problems in the way plants and facilities treat water can be often overlooked. Here are 4 of the most common issues encountered in the overall system of quality water treatment and in water treatment plants:
Maintenance Issues
Water treatment technology, facilities, and systems must always be kept in check, inspected, and maintained. Otherwise, neglect of these protocols may cause serious implications for the overall quality and safety of water treatment processes. Failing to perform regular maintenance on equipment and other assets used can result in costly repairs, grave damage to systems, and compromised human safety.
Inefficient Bacterial Control
While some bacteria are essential to water treatment operations, failing to monitor and manage bacterial growth can endanger the quality of water. Hence, having a tested and proven system of bacterial control helps avoid such a risk and hamper the cycle of water treatment.
Inadequate Training
Those working in water treatment plants or facilities, such as operators and specialists, deal with complex, highly technological processes. As such, there’s a need to prevent any misunderstanding of certain aspects of work due to poor training. Compromised quality of training can affect not just the safety of workers but also the quality of the overall treatment cycle.
Poor Monitoring and Recordkeeping
The home water treatment industry has responded to recent public concern over water quality by introducing a wide variety of home water treatment products into the marketplace. When faced with so many choices, consumers wonder what, if any, water treatment system they need. The various methods for treating water and some of the advantages and disadvantages of those methods are described in this bulletin. This is not an endorsement of any particular method or product for treating water in the home.
Reviewed and adapted for Missouri by Wanda Eubank, Jerry D. Carpenter, and Beverly A. Maltsberger, MU, and Nix Anderson, Missouri Department of Health, from Buying Home Water Treatment Equipment by Adel L. Pfeil, Department of Consumer Sciences and Retailing, Purdue University.
If you are on a public drinking water supply, it most likely meets national safety standards. Home treatment should not be needed for health protection. Homeowners using a private water supply are responsible for monitoring the quality of their own drinking water supply. Water treatment devices can improve the quality of water by reducing health hazards such as bacteria, chemical pollutants and other toxic substances, or help remove nuisance problems, such as odors or hardness.
Before considering any treatment devices, you should know the quality of your water supply. Odor and hardness problems can sometimes be detected by simple observation. Detection of bacteria, potentially toxic substances and other contaminants usually requires laboratory-conducted tests. If any undesirable qualities are identified in the water, the problem can often be solved by repairing or replacing the existing water system or treating the home water supply.
Locating a safe water supply is usually the best solution to combat a health risk. When persistently contaminated water poses a health threat or makes the water unusable, consider the following options: correct well construction faults, eliminate sources of contamination, install a new private well, connect to a public water supply or develop a community water system. After considering all of the options, a home water treatment system may be the most economical choice. Be sure the system you select bears the mark of the National Sanitation Foundation (NSF).
Before purchasing a system, you should know how the various systems work, what problems they address and the maintenance required. If more than one problem exists, treating water can become complicated. Purchasing water for drinking and cooking may be more cost effective than owning and maintaining equipment.
Water treatment systems generally use one or a combination of these five basic categories:
- Disinfection methods (chlorination, ultraviolet light, etc.).
- Filtration, including activated carbon filters.
- Reverse osmosis.
- Distillation.
- Ion exchange (water softeners).
Disinfection
Disinfection methods kill most of the harmful bacteria, viruses, cysts and worms found in water that can cause acute illness. Disinfection methods include chlorination, pasteurization, ultraviolet light and boiling
Chlorination
The most common, oldest and relatively inexpensive method used to disinfect water is chlorination. A chemical feed pump continuously dispenses chlorine chemicals into the water supply. Chlorine, an oxidizing agent, kills most bacteria and some viruses. In the proper concentrations and under adequate exposure time, chlorine is an excellent disinfectant.
However, care must be taken to ensure that only clean, clear water is used. Chlorine reacts with certain metals and organic matter in the water. The major problem with chlorination is the potential formation of hazardous, chlorinated, organic chemicals (trihalomethanes) when the chlorine reacts with organic molecules in the water supply. Using an activated carbon filter after chlorination will remove excess chlorine and limited amounts of chlorinated chemicals formed. Chlorination may also oxidize and remove some color and odor-causing substances including some iron and hydrogen sulfide.
The chemical feed pump requires frequent maintenance. The chemical reservoir must be kept filled and the pump checked at regular intervals for worn parts.
Pasteurization
With pasteurization, water is heated to kill bacteria, viruses, cysts and worms. The limited efficiency of the heat exchange makes pasteurization expensive. Pasteurization does not leave behind a residual product which continues to disinfect beyond the immediate treatment period.
Ultraviolet radiation (UV)
Low-pressure mercury arc lamps produce ultraviolet light, which has germicidal properties. The radiation kills or deactivates pathogens. Bacteria are killed with relatively low amounts of radiation, viruses are more resistant, and cysts and worms are unaffected.
The lamp's efficiency decreases with age and must be replaced annually. Color, turbidity and organic impurities in the water also interfere with transmission of ultraviolet energy and may reduce efficiency to unsafe levels. Also, radiation leaves no residual product that continues to disinfect beyond the treatment period.
Boiling
Boiling water for three minutes kills bacteria, including disease-causing organisms and giardia cysts. However, boiling concentrates inorganic impurities such as nitrate and sulfates. Boiled water also tastes flat because the carbon dioxide is removed.
Filtration
Filter systems are a relatively simple and effective way to control a variety of contaminants. These include mechanical filters, activated carbon filters, oxidizing filters and neutralizing filters. Filtration systems are designed for use only on potable water. This means that your water supply should be clean, uncontaminated and suitable for drinking.
Mechanical filters (microfiltration)
Mechanical filters remove suspended material from water, including sand, silt, clay and organic matter. They do not remove dissolved or very fine particles and are often used in combination with other treatment equipment. Filters are commonly of fabric, fiber, ceramic or other screening material. Mechanical filters can be cartridge units, mounted in a single waterline or on a tap, or tank units, which treat an entire household water supply. The filters must be serviced periodically.
Activated carbon filters
Activated carbon filters absorb impurities as they pass through a carbon cartridge. Generally, they are used to eliminate undesirable odors and tastes, organic compounds and to remove residual chlorine. Most inorganic chemicals, metals, microorganisms and nitrates are not removed by the filters.
Carbon filters also remove some potentially hazardous contaminants such as radon gas, many dissolved organic chemicals and trihalomethanes. If low levels of these contaminants exist, a whole-house unit can be used. However, these filters are not designed to remove persistently high levels of these contaminants. When contamination cannot be eliminated, an alternative water supply may be the safest solution.
The carbon filter loses its effectiveness as it becomes saturated with contaminants and must be replaced on a regular basis. Using the filter longer than its rated lifetime may cause contaminants to be flushed into the drinking water. Before purchasing the unit, ask the dealer if the filter can be replaced, the frequency of replacement, where replacement filters may be purchased and how much they cost.
The material in an activated carbon filter provides a growth surface for certain bacteria. If the filter has not been used for five or more days, simply run chlorinated water through the filter for at least 30 seconds before use.
Some manufacturers claim the addition of silver in their carbon filters will reduce or prevent bacteria growth. These carbon filters are registered as bacteriostatic by the United States Environmental Protection Agency (EPA) due to a requirement by the Federal Insecticide, Fungicide and Rodenticide Act. The required registration indicates the filter does not release excessive amounts of silver. The EPA has not endorsed these methods for reducing bacteria in the filter or in the water. Furthermore, a bacteriostatic carbon filter is not adequate to treat water that is microbially unsafe.
Oxidizing filters
Oxidizing filters remove iron, manganese and hydrogen sulfide (rotten egg odor). A manganese zeolite-coated filter causes dissolved iron and manganese to form particles the filter then traps. These filters are useful in removing iron if a water softener is not wanted. The filter usually treats the entire household water supply. Periodically, the filter must be rinsed with a chemical solution to remove the accumulated iron and manganese.
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Neutralizing filters
Neutralizing filters treat acidic water. The filter treats all of the home water supply by passing it through limestone chips or other neutralizing agent. Where acidic water does occur, it can leach lead, copper or other toxic metals from household pipes into the water supply.
Two potential problems occur with the filter. First, it may increase water hardness. Secondly, acidic water may intensify any iron problems already present in the water supply. The filter requires little maintenance except the need to occasionally replace the limestone chips.
Reverse osmosis
Reverse osmosis pressurizes and passes impure water through a semi-permeable membrane and removes many of the impurities (approximately 90 percent free of mineral and biological contaminants). The quality of the membrane and the pressure of the water help determine how effectively the water separates the contaminants.
Reverse osmosis (RO) units remove substantial amounts of most inorganic chemicals (such as salts, metals and minerals), most microorganisms and many organic chemicals. They do not effectively remove some organic compounds such as nitrate; they will reduce levels somewhat.
Mechanical filters and activated carbon filters are most always used with an RO unit. First, the mechanical filter removes dirt, sediment and other impurities that clog the reverse osmosis membrane. The RO unit is installed next. An activated carbon filter then removes some organic compounds which pass through the RO unit. Nitrates, however, will pass through carbon filters.
Reverse osmosis units use large amounts of water. Typically, about 75 percent or more of the water put into RO units is discarded with the contaminants. These systems may not be appropriate for households with a limited water supply. These units are expensive to purchase and require regular maintenance. Usually they are connected to a cooking and drinking line only and installed under the kitchen sink. Regular testing of the water supply is necessary to make sure the membrane is intact.
Distillation
Distillation heats water until it vaporizes as steam. Minerals, bacteria and other substances are left behind when the steam recondenses into relatively pure water. Distillers remove bacteria, minerals, trace amounts of metals, many organic chemicals and nitrate. Some stills allow contaminants with boiling points lower than water (some pesticides and volatile solvents) to vaporize with the water and recondense with the distilled water. A vented distiller avoids this problem. Distillers also remove beneficial minerals and make water taste flat or bland.
The distillation process is very slow (daily capacity is usually between two and five gallons). Approximately five gallons of tap water are required to produce one gallon of distilled water. Stills are relatively expensive. They require frequent cleaning and may be difficult to keep clean. The maintenance requirements and electricity consumption should be major considerations when purchasing a distiller.
Ion exchange (water softeners)
A common problem of water supplies is hardness, mainly caused by excess calcium and magnesium. Ion exchange systems soften hard water by removing the minerals causing hardness. These hardness minerals may interfere with the cleaning action of soaps and detergents and cause scale buildup in hot water pipes, water heaters and fixtures. The system also effectively removes some iron, manganese and many heavy metals.
The hard water is pumped through a tank containing an exchange resin. Sodium on the exchange resin replaces the hardness minerals. The sodium remains in soluble form in the softened water. Persons with heart problems should discuss this issue with a physician who will need to know the sodium level in the existing household supply of softened water.
To function properly, the resin tank must be periodically flushed (or recharged) with a solution of sodium chloride (salt). Some softeners automatically recharge the tank either on a regular schedule or when an electronic sensor detects that the resin needs to be recharged. With automatic recharge you only need to keep the sodium storage container filled. Other softeners must be recharged manually and are usually serviced by water treatment companies.
Purchasing considerations
Before buying a water treatment system, know the quality of your water supply and if treatment is needed. Consider the simplest and most economical solution to the problem. Removing the source of contamination, obtaining a new source of drinking water, or treating the water with a water treatment system may be appropriate solutions.
When purchasing a treatment system, ask the following questions
- What testing is needed to evaluate my water supply?
There is no single test to determine if water is safe. On-site demonstrations are not an accurate indicator of contaminant levels. Test water for suspected contaminants through a certified water testing laboratory.
- Is the system designed to treat the specific water quality problem?
Check the NSF rating for performance standards of water-treatment devices.
- How many gallons of treated water does the unit produce per day?
Is the amount sufficient for your household needs? If water need is low, purchasing bottled water may be more cost effective than purchasing water treatment equipment.
- Is there a sufficient water supply for the treatment unit to work properly?
Distillation and RO units use large amounts of water.
- How will you know if the unit is not working properly?
An alarm or indicator light should alert you to a malfunction.
- What maintenance is required?
All equipment requires maintenance and service. The more treatment you have, the greater your responsibility.
- What routine servicing is offered?
Is a service contract available? Unless you are unusually dedicated, automated and self-monitoring features or dealer's service agreements are recommended to ensure correct operation and high quality water.
- Is there a warranty?
What does it cover? Make sure any claims about the performance of the treatment unit are clearly identified in writing.
- What is the total cost?
Consider the expected life, purchase price, installation cost, maintenance cost and operation cost. Every treatment system has its own advantages and disadvantages.
- If you rent the equipment, does your agreement include an option-to-buy provision?
Compare the rental cost to the purchase price and expected life of the equipment.
Some of the more common treatment methods used to handle certain contaminants are mentioned in Table 1. This is a general guide and does not contain all of the potential treatment techniques or contaminants. The concentration of the contaminant and combination of various contaminants can have a major impact on the effectiveness of the treatment method.
Table 1
Solutions to water quality problems
Bacteria
First choice or best treatment option
- Locate and remove source of contaminants
Second choice
Third choices
- Chemical feeder (Continuous disinfection: chlorination)
- Distillation
Acidity/alkalinity/pH
First choice or best treatment options
- Chemical feeder
- Neutralizing filter
Sediment/asbestos
First choice or best treatment option
Second choices
- Reverse osmosis
- Distillation
Common inorganic chemicals
First choice or best treatment options
- Reverse osmosis
- Distillation
Heavy metals such as cadmium, chromium, lead, mercury, silver, etc.
First choice or best treatment options
- Reverse osmosis
- Distillation
Second choice
- Activated carbon filter (Removes small amounts of some contaminants.) A carbon filter — also called a taste and odor filter — is an ideal medium for bacteria growth and should be used only on water supplies that are continuously disinfected or known to be free of bacteria. Usually a two-stage carbon filter.
- Chemical contaminant filter (Removes small amounts of some contaminants.)
Nitrate/nitrite
First choice or best treatment option
- Locate and remove source of contaminants
Second choice
Third choices
- Reverse osmosis (Requires a semi-permeable membrane, pressure over 60 psi and regular monitoring of salts to ensure effective removal by reverse osmosis. Reverse osmosis reduces but does not remove all nitrates.)
- Distillation
Sodium
First choice or best treatment option
Second choices
- Reverse osmosis
- Distillation
Total dissolved solids (salts)
First choice or best treatment options
- Reverse osmosis
- Distillation
Iron and manganese
First choice or best treatment option
- Zeolite-ion exchange softening (Iron removal capacity of softening depends on amounts of iron, filter capacity, and type of exchange media. Higher concentrations require use of special iron treatment equipment, i.e., iron filter.)
Second choice
- Resin-ion exchange softening (Iron removal capacity of softening depends on amounts of iron, filter capacity, and type of exchange media. Higher concentrations require use of special iron treatment equipment, i.e., iron filter.)
Hardness
First choice or best treatment option
- Resin-ion exchange softening
Second choice
- Zeolite-ion exchange softening
Odor/taste
First choice or best treatment options
- Activated carbon filter (A carbon filter — also called a taste and odor filter — is an ideal medium for bacteria growth and should be used only on water supplies that are continuously disinfected or known to be free of bacteria. Iron removal capacity of softening depends on amounts of iron, filter capacity, and type of exchange media. Usually a two-stage carbon filter. Higher concentrations require use of special iron treatment equipment, i.e., iron filter.)
- Chemical contaminant filter (Iron removal capacity of softening depends on amounts of iron, filter capacity, and type of exchange media. Higher concentrations require use of special iron treatment equipment, i.e., iron filter.)
Pesticides/VOCs
First choice or best treatment option
Second choice
- Chemical contaminant filter
Third choices
- Reverse osmosis
- Distillation (A vented distiller is necessary for this process.)
Fourth choice
- Activated carbon filter (A carbon filter — also called a taste and odor filter — is an ideal medium for bacteria growth and should be used only on water supplies that are continuously disinfected or known to be free of bacteria. Usually a two-stage carbon filter.)
Turbidity
First choice or best treatment option
Second choice
- Activated carbon filter (A carbon filter — also called a taste and odor filter — is an ideal medium for bacteria growth and should be used only on water supplies that are continuously disinfected or known to be free of bacteria. Usually a two-stage carbon filter.)
Third choice
References
- Shaw, Byron H. and James O. Peterson, Improving Your Drinking Water Quality, Cooperative Extension Service, University of Wisconsin-Madison, Madison, Wisconsin.
- Water Treatment Fundamentals, , Water Quality Association Education Services.
This MU publication — previously named WQ Understanding Home Water Treatment Systems — was reviewed and adapted for Missouri by Wanda Eubank, Jerry D. Carpenter and Beverly A. Maltsberger, University of Missouri, and Nix Anderson, Missouri Department of Health, from “Buying Home Water Treatment Equipment” by Adel L. Pfeil, Department of Consumer Sciences and Retailing, Purdue University
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