A glass of pure fresh water being poured into a glass.

How to Purify Water – The Different Purification Methods

Water everywhere and not a drop to drink. One of our most precious resources in this world falls freely from the sky, encompasses most of the surface of the Earth, and is delivered to us through a convenient tap in our homes.

However, as temperatures of our world heat up and pollution seems to be at an ever-alarming high, our precious water sources are dwindling. Without clean water, waterborne diseases can surface and cause havoc on our bodies. These are diseases such as diarrhea, typhoid, dysentery, guinea worm disease, and cholera. In some cases, impure water can cause death. 

The United States has the advantage of being a country where laws are in effect that set the standard for pure, drinkable water. Having this kind of structure in your country can feel like a relief. However, nothing is guaranteed. Concerns about fluoride in our drinking water have surfaced, among other things. 

Take the case of Flint, Michigan for example. The corrosion of the city’s water pipes led to the addition of lead in the citizen’s water supply. This ended up affecting thousands of people with harmful lead-poisoning and cost them years without clean water. 

This can be an important lesson to all of us to not only monitor our water quality but also to know who to purify water if faced with an emergency. In this article, we will touch on several methods for eliminating harmful contaminants in your water. Ranging from the more expensive, permanent solutions, to methods you can use in a pinch, we will provide you several ways to keep your water safe. Here are some of the most common methods for purifying water: 

  • Filtration
  • Reverse Osmosis
  • UV Light
  • Sun
  • Distillation
  • Boiling
  • Chlorine/Bleach
  • Iodine


Filters are the most common way to purify water for personal use. They are quick and easy to use, as well as come in a variety of shapes and sizes. You can use portable filters or install a water filtration system for your whole house. Filters remove some heavy metals, sediment, bacteria, and large parasites such as Cryptosporidium. They do not, however, protect against viruses. Another downside is that filters must be replaced, sometimes as soon as every 2 months. 

Filters are made up of highly porous activated carbon and charcoal formed in a cylinder or round shape. These pore sizes are measured in microns, the size determining what contaminants will be filtered. The typical pore size is 0.2 microns and will block heavy metals like lead and copper.

Water filtration works by absorbing the contaminants when water flows through the carbon. The purified water then passes through onto the other side. Active carbon can remove a total of 81 chemicals from water, 14 of them pesticides and 12 of them herbicides. It also gets rid of the smell of chlorine that comes from city water. 

If you are going on an outdoor adventure or are traveling, a portable water filter might be the best bet for you. If you happen to be camping by a freshwater lake, there is no need to bring gallons of water with you. You can use your water filter to cleanse the water and ensure it is clean and safe for drinking. 

Reverse Osmosis

Another water purification process is reverse osmosis, also referred to as RO. The process works when unfiltered water is forced through a semipermeable membrane that removes up to 98% of total dissolved solids (TDS). The water moves from the more concentrated side of the membrane to the less concentrated side, removing contaminants along the way. The end product is fresh water called permeate. The leftover water is called waste or brine. 

Not only does the membrane work to block contaminants, but there are additional filters used in the process. Additionally, the RO system may have a sediment filter, a carbon filter, or both. These filters are either used before or after the water has cleared through the membrane. The sediment filter eliminates dirt, dust, and rust. The carbon filter decreases volatile organic compounds (VOCs), chlorine, and other contaminants to contribute to bad taste or odor.

Once the water has gone through the varying layers of filtration, it flows to a storage tank where it is held until used. Once the tank has been filled, it shuts off. When you turn on your faucet, the water goes through a postfilter to once again ensure against impurities. And finally, the filtered water arrives in your glass.

A close-up shot of a UV light sterilization lamp.

Achieving optimum disinfection of water via ultra-violet (UV) light depends on its frequency and intensity.

UV Light

If you have ever gotten a sunburn, you’ve been affected by ultraviolet light from the sun. Such a powerful force can also be used to decontaminate water. The use of UV light has been standard for city water due to its quick and effective application. It is now also available to the public. These purification systems emit more UV light than what comes naturally from the sun, making them more effective than solar purification. 

UV water purification occurs when water flows through a chamber exposed to UV light radiation. Any harmful bacteria, viruses, molds, or parasites will be killed instantly. This method can kill up to 99.99% of microorganisms. This system kills more viruses like Norovirus and Hepatitis than chlorine and will do so much quicker. The water itself will have no added smells or tastes, which is another benefit. It will, however, get rid of heavy metals and particles, rendering the necessity of another system for such contaminants. 

The UV light is only as effective as how intense or frequently it is emitted. The more intense, the better it will be at getting rid of microorganisms. This can be difficult because such a process can be expensive, requiring a lot of electricity. Additionally, the system requires a lot of cleaning and maintenance to keep it running efficiently. 


A cheap yet effective process for water purification is our good old sun. Solar purification can be used when no other methods are available; perhaps for camping the great outdoors or in an emergency. As with the previous method, the UV rays are used to kill bacteria, parasites, and viruses. This energy from the sun can disinfect lake and river water if left exposed for enough time. However, one must be cautious of this as certain water sources like stagnant pond water can be a breeding ground for bacteria and mosquitoes. Therefore not all water sources are safe to use for this method. 

Some common bacteria that can be eliminated with this method include E. coli, cholera, salmonella. It can also kill parasites like Giardia and Cryptosporidium and viruses like rotavirus.

You can use PET plastic bottles for the disinfection of water, per the World Health Organization (WHO). The water you use should be from a clean, well-known source, like a lake or river. Stay away from water that is stagnant, smelly, oily, or located near bathrooms or sewers. Be sure the water is not polluted with chemicals. The method recommended by WHO uses UV sunlight and high temperature to kill harmful pathogens in water. 

If there is any dirt, mud, or debris, pour the water through a few layers of cloth to filter it out. Repeat until the water is as clear as possible. The sun’s rays are unable to pass through cloudy water, so water clarity is key. Use a clean Polyethylene Terephthalate (PET) bottle, which will have a recycle code #1 on the bottom. Fill the bottle ⅔ full and shake for 20 to 30 seconds. This allows oxygen to saturate into the water, killing some germs. Then continue filling up the bottle to the top and lay it down in the full sun. Laying the bottle on its side allows the sun’s rays to reach the depth of the bottle, not just the surface. 

This process is best performed on a reflective surface on a sunny day. If there is full sun with just a few clouds in the sky, keep the bottle out for 6 hours. If half of the sky is covered with clouds, the process will take about 2 days.

A bottle filled with distilled water for use in laboratories.

Bottled distilled water can usually be found in supermarkets or pharmacies, and home water distillers are available as well.


Distillation of water is a specialized form of purification and can be done easily and cheaply from home. The process of distillation occurs from the vaporization of boiling water. The vapor is funneled into a condenser where it is cooled. When the vapor turns back into liquid form, it flows into a receiving container and the contaminants are left behind. This process reduces sediment, metals, and biological contaminants. Some units are combined with activated carbon filtration. Acting in combination, these distillers can filter out lead, fluoride, mercury, arsenic, asbestos, and radium. This process provides clean water that is about 98% free of contaminants.  

Distilled water can be better for you than some tap water. However, be aware that distilling water can rid it of harmful impurities, but it also does away with beneficial minerals and electrolytes such as calcium, sodium, and magnesium. Only hydrogen and oxygen are left behind, giving the water a bland flavor. This fact makes it useful for other various household needs such as watering plants, steam irons, car cooling systems, aquariums, and certain medical devices. 

Types of water distillers include household distillers, plumbing distillers, and commercial distillers. Some units even work by way of solar power to reduce the cost of heat sources and are environmentally friendly. Household distillers are portable and can set on your kitchen counter or office. Pour water into the system and the water will automatically be distilled into a reserve for use. Plumbing distillers are installed into your whole house system or at a point of use. Some maintenance is required with the option. Commercial distillers involve multiple boiling chambers and are used for high-output facilities.


If you don’t have safe drinking water, you can boil your water to ensure it is free of viruses, pathogenic bacteria, and protozoa. The EPA says that as with the laws of pasteurization, pathogens cannot survive above 158 degrees Fahrenheit if the water is boiled for long enough. Keep in mind that boiling water will not destroy other contaminants like heavy metals, salts, and most chemicals. The taste of boiled water may be flat or bland. You can improve the taste by pouring it from one container to another and then let it sit for a few hours. You can also add a pinch of salt per quart of boiled water. 

To boil cloudy water, first filter it through a clean cloth, paper towel, or coffee filter. You can also simply allow it to settle and then draw from the clear water. Next, bring the water to a rolling boil for 1 minute. If you are at an elevation over 6,500 feet, boil for 3 minutes. Allow the water to cool. Then store it in a sanitized and clean container with a tight lid to prevent bacteria and microbes from entering in. 

To boil clear water, simply keep it at a rolling boil for 1 minute. If you are at an elevation above 6,500 feet, boil for 3 minutes. Let it cool, then store it in a sanitized and clean container with a tight lid to prevent the infestation of bacteria and microbes.


Chlorine is a common water purifier used for city water treatment. It can make water potable by killing off bacteria, viruses, and parasite cysts like Giardia. It is not, however, effective against Cryptosporidium or Cyclosporum. This method is helpful in a situation where water is coming straight from the earth, like on a camping adventure.

You can use bleach, a household grade chlorine to provide clean drinking water. Bleach has 4 to 6% chlorine concentration, the active ingredient being Sodium Hypochlorite. Depending on the concentration level will determine how the product is used. Make sure to use unscented bleach.

For the disinfection of water using household bleach, mix 2 drops of bleach in a liter of water. This means 8 drops to a gallon. Let it stand for half an hour, and then the water will be safe for consumption. If you’d like to eliminate Giardia, let sit for 45 minutes. If you are treating the water against Norovirus, you will need to let the water sit for an hour. 

One alternative to the use of household bleach is water purification tablets. These may contain chlorine, iodine, chlorine dioxide, or other disinfecting properties in their pre-dosed tablets. Simply drop the necessary amount of tablets in the water and let it sit between 30 and 45 minutes. This method is particularly convenient for travelers in foreign countries where the water sources are unknown, or for spending time in nature where you can’t bring along gallons of water. If you are unsure of a water source, having a pack of water purification tablets can be a lightweight, compact, and inexpensive investment.

3D rendering of a capsule with iodine printed on it.

Iodine kills many, but not all, of the most common pathogens present in natural freshwater sources.


In a worst-case scenario, an iodine treatment can be used to purify water. Iodine is commonly used as a disinfectant, as well as to prevent issues with the thyroid. You can find iodine in the form of tablets, crystals, tinctures, or liquids. It can kill bacteria and viruses at the cellular level, as well as Giardia if it sits for 50 minutes. It does not, however, work against Cryptosporidium. 

Since iodine is very strong, we only recommend such treatment be done in an emergency. It can be deadly if consumed in heavy doses. It should not be used by children, pregnant women, people with thyroid problems, iodine, or shellfish allergies. Additionally, water purified with iodine has an unpleasant taste and is therefore not enjoyable to drink. 

If you need to purify water in a pinch, mix 2 drops of iodine tincture in a quart of water. The water must be clear. If it is cloudy, apply 10 drops to a quart instead. Allow the mixture to sit for half an hour before use. If you are using iodine in crystal or tablet form, follow the instructions of the manufacturer. Keep iodine in a dark bottle since it is sensitive to light.

Being Prepared

If you can afford it, installing a filtration, UV, or reverse osmosis system in your home can be one of the best investments you can make. Having a steady flow of clean water will ensure not only your protection from harmful contaminants that affect your health but these options will also give you peace of mind. What about emergencies? The distillation or boiling of untreated water can work when you must go without water but still have access to a heat source. Chlorine water purification tablets work well when you are traveling away from home. Finally, solar power and iodine can be used as a last resort if all else fails. 

In our ever-changing world, knowing how to provide yourself and your family with pure drinking water can be a great advantage. Being prepared for any disaster emergency or survival scenario is always a good idea to keep the clean water flowing.

Joshua Perkins

Joshua spent ten years as a water systems technician in California before settling down with his wife and two young children in Nashville in 2018. Through all of his experience, he learned the benefits and shortfalls of so many different types of water filtration systems, from pitchers to whole-house installations. He started Water Filter Authority in 2019 to empower other families to make the right decision for their long-term health and wellness.