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Types of Water Contaminants & How to Make Water Safe

Water Purification

We must be ready to treat unsafe water from our home faucets and non-potable water from outside sources when needed. Preparing for these two possibilities will help shore up our water supply if we know how to successfully treat undrinkable water. To do this, we must first be able to identify the pathogens and chemical compounds we are dealing with.

The Safe Drinking Water Act defines a "contaminant" as any physical, chemical, biological, or radiological substance or matter in water. Most contaminants cause harm when ingested rather than absorbed.

Water Purification
General Categories of Drinking Water Contaminants

Physical

Physical contaminants affect the appearance and properties of water. They may make water look dirty or unappetizing, but they typically do not cause harm if swallowed. Examples include sediment and organic material suspended in the water from lakes, rivers, and streams.

Effective
Sediment filters: 5 to 50-micron
Sediment filters are the only thing necessary. The most common size filter for this purpose is 5-microns.
Learn more about sediment filters

Chemical

Chemical contaminants can be naturally occurring or man-made. Natural pollutants often result from runoff, erosion, or biological processes, while man-made chemicals can arise from spills, improper disposal, or corrosion of metal pipes.

Effective
Distillation
Will remove all forms of chemical contaminants
Reverse Osmosis
Effective against: sodium, chloride, copper, chromium, and lead.
Moderately effective against: arsenic fluoride, radium, sulfate, calcium, magnesium, potassium, nitrate, and phosphorous.
Filter (0.001-micron)
Moderately effective
Not Effective
UV Systems, Disinfecting, Boiling, Filters (0.01-micron and higher), Solar
Learn more about these treatment methods

Biological

Biological contaminants are microorganisms such as viruses, bacteria, and parasites. These pathogens are invisible to the naked eye, making water testing essential because even trace amounts can cause severe illness. Examples include E. coli, Salmonella, Vibrio cholerae, typhoid bacteria, Giardia, Cryptosporidium, and various worm infections.

Effective against parasites, bacteria, and viruses
Boiling
Reverse Osmosis
Distillation
Ultraviolet
Solar
Filter: (.001-micron)
Effective against 2 of 3
Chemical Disinfection
Effective against: bacteria and viruses (use a 1-micron filter to treat parasites)
Filter (.01-micron)
Effective against: parasites, bacteria (some viruses)
Effective against 1
Filter (.1-micron)
Effective against: parasites (some bacteria)
Filter (1-micron)
Effective against: parasites
Learn more about these treatment methods

Radiological

Radiological contaminants in public drinking water often occur naturally—radioactive elements like radium and uranium can dissolve from rocks and soil. These contaminants can pose significant health risks if consumed over long periods. Man-made radiological contaminants may result from improper disposal of radioactive wastes or nuclear incidents.

Reverse Osmosis
Learn more about these treatment methods
Water Purification
Water Purification Steps

Signs of Unsafe Water

Contaminated water often has a bad odor, unpleasant taste, and can sometimes appear cloudy or discolored. It may contain microorganisms such as bacteria, viruses, or parasites that can cause serious health issues like dysentery, typhoid, cholera, hepatitis, and other illnesses. In some cases, harmful chemicals or heavy metals might also be present, further compromising water safety.

Treating Water Contamination

If your water source is of uncertain quality, it’s essential to purify it before use to protect your health. This includes any water intended for drinking, dishwashing, oral hygiene, food preparation, or making baby formula.

Purification typically involves a two-step process: first, removal of visible debris and sediment using filtration; then, elimination of pathogens through boiling, chemical treatment, or other water purification systems.

Step 1: Debris Removal

Debris removal filters out contaminants that cause water to appear dirty or cloudy. While you can use a paper towel or coffee filter in a pinch, using a proper water filter is recommended. (Learn more below.)

Step 2: Pathogen Elimination

Pathogens like protozoa, bacteria, and viruses must be removed or killed. Some methods can kill all three at one time, while others need to be used together to successfully purify the infected water. (Learn more below.)

Water Purification
Debris Removal

Sediment Filtration

Debris removal is achieved through filtration. Filters have various pore sizes measured in microns; contaminants larger than the pore size will be caught. A 5-micron sediment filter is the most common, trapping particles larger than 5 microns, though smaller contaminants may pass through.

Some of the most dangerous contaminants in water are smaller than this. So, once the larger sediment has been removed, it's time to remove smaller contaminants if they are present.

Water Purification
Pathogen Elimination

Click on each method to learn more.

Boiling Water

Boiling is the surest method to kill disease-causing germs, including viruses, bacteria, and parasites. It is seen as the safest method of treating water because you are not adding chemicals into the water during the process, as most other methods do. It is ineffective at removing toxins.

Directions

In a large pot or kettle:

  • Bring clear water to a rolling boil for 1 minute (at elevations above 6,500 feet, boil for 3 minutes).
  • Be aware that some water will evaporate.
  • Allow the water to cool before drinking.

Tips for better tasting water

Boiled water can taste better by doing one of the following:

  • Pour the water back and forth between two clean containers, then allow it to stand for a few hours. This aerates the water and improves taste.
  • Add a pinch of salt per quart or liter of boiled water.

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Chemical Disinfection

Chemical disinfectants such as bleach, chlorine dioxide, and iodine are effective at killing viruses and bacteria, as well as the giardia parasite. Note that these disinfectants are generally not effective against Cryptosporidium. You may follow chemical disinfection with a 1-micron filter for additional removal of certain parasites.

Popular chemical disinfectants include bleach, chlorine dioxide (in tablet form), iodine (available as a 2% liquid solution or in tablet form), and Pool Shock (as an alternative, used only if standard bleach is unavailable). (See below for details.)

Chlorine Bleach

Unscented liquid chlorine bleach in the United States typically contains 6% to 8.25% sodium hypochlorite. Always read the label to determine the concentration and adjust the dosage accordingly.

Directions

  • Select a measuring device (dropper, mL syringe, or teaspoon set).
  • Add the appropriate amount of bleach to your water – see mixing amounts below.
  • Stir thoroughly.
  • Allow the mixture to stand for at least 30 minutes before drinking.
  • Store the disinfected water in clean, sanitized containers with tight covers.

Mixing Amounts

6.25% to 8.25% Sodium Hypochlorite
Per quart or liter
  • - Add 2 drops (≈0.1 mL)*
Per 1 gallon
  • - Add 8 drops (≈0.5 mL or 1/8 tsp)
Per 5 gallons
  • - Add 40 drops (≈2.5 mL or 1/2 tsp)
* too small to measure
1% Sodium Hypochlorite
Per quart or liter
  • - Add 10 drops (≈0.5 mL or 1/8 tsp)
Per 1 gallon
  • - Add 40 drops (≈2.5 mL or 1/2 tsp)
Per 5 gallons
  • - Add 200 drops (≈12.5 mL or 2.5 tsp)
Tip

For easier measuring follow these tips:

  • Avoid using a teaspoon for small volumes; use a more precise measuring method.
  • Keep your measuring device with your bleach supply.

DOWNLOAD INSTRUCTIONS
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Chlorine Dioxide

Chlorine Dioxide is a chemical compound used in public water-treatment facilities to make water safe for drinking. It is not the same thing as chlorine bleach though it can produce some of the same results.

Comes in tablet form

Typically, one tablet can purify 1-2 liters of water in 30 minutes.

PROS
  • Fast acting
  • Popular method for on-the-go water disinfection.
  • Convenient pre-portioned tablets that are easy and safe to use (follow package instructions).
  • No unpleasant taste or odor.

Shelf life: 4 years from manufacture.

Iodine

Iodine, available as a 2% liquid solution or in tablet form, is moderately effective as a disinfectant.

Liquid 2% Solution

Add five drops per quart or liter; if water is cloudy, add 10 drops. Stir and let stand for 30 minutes.

Tablet Form

One tablet can purify 1-2 liters of water in 30 minutes.

PROS
  • The least expensive tablet option compared to chlorine dioxide.
CONS
  • Unpleasant taste (consider adding a powdered drink mix).
  • Not recommended for pregnant women, individuals with thyroid issues, or those allergic to iodine.
  • Not recommended for continuous use beyond a few weeks.

Shelf life: 4 years from manufacture.

Pool Shock

Pool shock is a chlorine-based product used for swimming pools. It can also be used to disinfect water if used correctly. It is a strong chemical and should only be used if your bleach has expired. Unlike bleach (which expires after 6–12 months), pool shock has an almost indefinite shelf life when stored properly. A 1-pound bag can disinfect up to 10,000 gallons. You can see why it’s a smart move to store this product with your other water purification supplies. If you run out of the other, this makes a great backup.

source: HTH

What to look for

Purchase pool shock containing 68% or higher Calcium Hypochlorite. Examples include: HTH Ultimate–Shock Treatment 7 in 1 and Ultima TKO. Remember, use it only as a backup option and follow all safety instructions.

DOWNLOAD INSTRUCTIONS
- place with your storage materials -

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Filtering of Pathogens

Different types of filters are designed to remove various contaminants, including viruses, bacteria, parasites, heavy metals, pesticides, and herbicides. However, the specific effectiveness depends on the filtration method and pore size also known as micron rating.

No single filter removes everything. Combining filtration methods provides the best protection. For emergency preparedness, it’s smart to have a reliable multi-stage system or a combination of filters on hand.

Filtration Methods & Micron Ratings

Filtration Method Micron Rating Contaminants Removed Limitations
Sediment Filtration 1 micron Large particulates (sediment, rust), some bacteria, some parasites Not effective against viruses; not full pathogen removal
Microfiltration 0.1 micron Most bacteria, parasites Viruses not removed
Ultrafiltration 0.01 micron Bacteria, parasites, some viruses Some small viruses may pass through
Nanofiltration 0.001 micron Bacteria, parasites, most viruses, organic compounds Some dissolved salts and small molecules may remain
Activated Carbon N/A (adsorption) Heavy metals, pesticides, herbicides, VOCs, improves taste and odor Does not remove pathogens (bacteria, parasites, viruses)
Reverse Osmosis (RO) 0.0001 micron Wide range: chemical contaminants, heavy metals, bacteria, parasites, nearly all viruses Slow process, requires water pressure, produces wastewater
Sediment Filter - 1 micron

Removes larger particulates (dirt, rust), and some bacteria and parasites. Not reliable for full pathogen removal.

Microfiltration - 0.1 micron

Removes most bacteria and parasites. Does not remove viruses.

Ultrafiltration - 0.01 micron

Removes bacteria, parasites, and some larger viruses. Small viruses may still pass through.

Nanofiltration - 0.001 micron

Removes bacteria, parasites, most viruses, and many organic compounds. Some dissolved salts and small molecules may pass through.

Activated Carbon Filter

Adsorbs heavy metals, pesticides, herbicides, and organic chemicals, and improves taste and odor. Does not remove bacteria, parasites, or viruses.

Reverse Osmosis - 0.0001 micron

Removes chemical contaminants, heavy metals, bacteria, parasites, and nearly all viruses. Though this is one of the most comprehensive filtration methods, keep in mind that it is a slow process, it requires water pressure, and produces wastewater.

Note: Filtration effectiveness varies by specific product design and maintenance. Be sure to always follow manufacturer guidance for safe water treatment.

Certified Filters

Testing

While the water filter industry is not regulated, strict health standards for drinking water have been put forth by the National Sanitation Foundation (NSF) and the American National Standards Institute (ANSI). Tests are conducted by accredited third parties against these high standards and are offered to any filtration company willing to pay. Filters that pass are given a certificate, ensuring consumers that the water filter they're buying meets the highest standards. Meaning, it can remove or reduce Crypto.

Certified Filters

To see which filters have received certification, look for one of the following the on-product labeling and the company's marketing materials.

  • Reverse Osmosis (with or without NSF 53 or NSF 58)
  • Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst removal
  • Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst reduction
Non-Certified Filters

Because testing to ANSI standards is very expensive and voluntary, some filtration companies simply won’t pay. That does not mean their filters are not good. These companies run their own tests and have documentation on what their filters can and cannot do. They just can't prove it with a testing certification. Before you purchase a filter from an uncertified source, read their documentation closely.

Be wary of the following labeling

There are many filters on the market that just don't do the job and take advantage of the consumer who does not know what to look for. Per the CDC, filters labeled with the following words may NOT be designed to remove Cryptosporidium (Crypto) and other dangerous pathogens.

  • - Nominal pore size of 1 micron or smaller
  • - One micron filter
  • - Effective against Giardia
  • - Effective against parasites
  • - Carbon filter
  • - Water purifier
  • - EPA approved (EPA does not approve or test filters)
  • - EPA registered (EPA does not register filters)
  • - Activated carbon
  • - Removes chlorine
  • - Ultraviolet light
  • - Pentaiodide resins
  • - Water softener
  • - Chlorinated
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Solar Disinfection

Solar Water Disinfection, also referred to as SODIS is a type of portable water purification system that uses solar energy to kill biological contaminants, namely viruses, bacteria, some parasites like Giardia, and worms. It is not effective against the more stubborn Cryptosporidium.

After enough exposure, the sun’s UV rays ultimately alter the DNA molecules of pathogens in the water. A process of photo-oxidation then destroys the microbes, preventing sickness and disease.

While it does destroy, it does not remove pathogens. If you would like to have that done, using a 1-micron filter can do that. Water contaminated with non-biological agents such as toxic chemicals or heavy metals requires other purification methods to make the water safe to drink as SODIS will not remove any other type of contamination.

Source: Wikipedia

Solar purification steps

  • #1 If necessary, filter the water to make it as clear as possible.
  • #2 Use PET plastic or glass bottles (a 2-liter soda bottle is acceptable).
  • #3 Ensure bottles are in good condition, washed, colorless, transparent, and free of labels.
  • #4 Fill the bottles with water and close the cap.
  • #5 Shake the bottles thoroughly to mix in oxygen.
  • #6 Expose the bottles to direct sunlight for at least 6 hours (or 2 full days under cloudy conditions).
  • #7 Store the water in the treated bottles until ready for use to minimize contamination risks.
  • #8 When needed, drink directly from the bottle or from a clean cup.

PROS
  • Relatively easy and inexpensive using readily available materials.
CONS
  • Requires 6 hours to 2 days of sunlight, limiting immediate availability.
  • Only inactivates biological contaminants—not chemical or radiological ones.

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Ultraviolet

Ultraviolet (UV) Treatment uses ultraviolet light to disinfect water and is effective against viruses, bacteria, and all parasites. High-dosage lamps are highly effective at treating these pathogens and differ from the other disinfectant methods in that the process is chemical-free. It is not a standalone method as it must be used with a pre-filtration system. The UV system is most effective when the water is clear and free of physical contaminants. The use of at least a 5-micron filter is sufficient. The next step is the UV treatment itself.

source: puritor.com

UV process

Contaminated water is exposed to germicidal ultraviolet light. The UV wavelength damages the DNA of living organisms, making them unable to reproduce which is what will make you sick. The higher the UV dosage, the more energy is delivered to treat contaminated water. Energy needs to reach a certain threshold to be sufficient to inactivate most microorganisms in the water.

While UV treatment purifies water by exposing living organisms to ultraviolet light, it does not filter them out. If you want to filter out the microorganisms themselves, an additional 1-micron filter is sufficient. (Don’t use this filter for pre-filtering as this can clog this smaller pore-sized filter.) UV systems are often paired with Reverse Osmosis Systems as well, to provide a complete purification process for the safest drinking water.

source: prathamfilter.in
UV System

Here's a simple look at the unit itself.

  • 1. An outer chamber encases the UV unit and is held together by 1 or 2 O-rings.
  • 2. Inside this chamber is a transparent glass quartz sleeve that holds a UV lamp.
  • 3. As water moves through the chamber, the UV lamp emits a germicidal wavelength of radiation through the glass and on to the water. This deactivates all living organisms.

source: excelwater.co.uk
Home Use

UV filters are compact and relatively easy to install and maintain. They can be connected to the main water supply line, and do not require any special tools or equipment. Once installed the UV systems work reliably around the clock. Water flows through the tank without the need for a holding tank or any reaction time. It is a set-it-and-forget-it type of system though you will need to replace the UV lamp once a year.

PROS
  • High-dosage systems can treat parasites that other disinfection methods cannot.
  • Every drop of water that enters the UV system is purified.
  • Requires very little energy - uses about the same energy as it would run a 60-watt light bulb.
  • Protection during natural disasters. When city water is compromised, a UV system keeps your drinking water safe.
CONS
  • High dosage UV filters can be expensive.
  • Low dosage units may not effectively inactivate some viruses, spores, and cysts. If you are going to invest in this method, be sure to get the high dosage unit.
  • UV water systems require electricity to operate so they will not work during a power outage.
  • May not be suitable for emergencies or survival needs unless the use of a generator is factored in.
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Distillation

Distillation is a process that relies on evaporation to purify water. Distillation Systems use a process of heating water to the boiling point and then collecting the water vapor as it condenses, leaving many of the contaminants behind. This process effectively kills viruses, bacteria, and all parasites.

The unit consists of three parts:

Boiling Chamber

Water enters and is heated to its boiling point; it forms steam and is vaporized. Inorganic compounds and large non-volatile organic molecules do not evaporate with the water and are left behind, separating out the contaminants.

Condensing Coils

The steam is collected and as it cools, it will then be converted back into its liquid form to form purified water.

Storage Tank

After purification the water is held here until it is used.

Distillation effectively removes:
  • Waterborne pathogens
  • Inorganic chemicals such as heavy metals and nitrates
  • Many organic chemicals
  • Soluble minerals
  • Particulates
PROS
  • It produces some of the purest potable water available.
CONS
  • Water treated with this method is stripped of important minerals which produces a flat taste.
  • The unit generates significant heat, which can be problematic in warmer conditions.
  • Low-volume units produce water slowly, while high-volume units are expensive and require substantial electricity.
  • Because it requires electricity, distillation may not be ideal for emergencies without a generator.
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Reverse Osmosis

Reverse Osmosis is a water-purifying treatment that uses pressure to filter contaminated water. As the pressurized water passes through a semi-permeable membrane, it stops almost anything larger than a water molecule from passing through. The use of sediment and carbon filters is used in this process as well.

Reverse Osmosis removes more than 90 to 99% of a wide range of contaminants, such as heavy metals, solvents, organic contaminants such as pesticides and herbicides, and pathogens including viruses, bacteria, and all parasites.

Home Application

You have two options when it comes to utilizing this water purification method at home. You can install a more robust under-counter system or a smaller countertop filter.

Under Counter System

The reverse osmosis system taps into the under-sink infrastructure you already have in place. As water passes through filters, it is sent to a holding tank that has also been placed under your sink to catch and store the newly purified water. A dedicated faucet, separate from the original, is installed on your sink and draws water from the storage tank below whenever you want access to your purified water.

Countertop System

A countertop reverse osmosis system is also available and is not any bigger than other appliances you already place on your counter. From your counter, you attach a feed line to your original faucet and the water is filtered through this countertop system. These systems are not as robust and can be quite slow in comparison, so if you are serious about using this method to purify water, an under-counter system may be the way to go.

PROS
  • Reverse Osmosis is the most effective eliminator of all disease-causing organisms and most chemical contaminants.
CONS
  • It removes sodium and healthy essential minerals. There are systems that will add them back in.
  • The process uses approximately 3 times as much water as it treats, which may be reflected on your water bill.
  • There may be some noticeable drop in water pressure.
  • This system is not a set and forget. It requires extensive care and maintenance.
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Water Purification
Water Testing Kits

Testing Your Water Supply

While stocking up on water purification tools is essential for emergency preparedness, it’s equally important to know what you’re treating. Not all water sources carry the same risks. Some may be contaminated with bacteria like E. coli or Salmonella, while others might be harboring other pathogens equally invisible to the eye. That’s where water testing kits come in. They can help you identify whether treatment is needed at all—and if so, which method is most appropriate.

DIY water test kits are widely available and easy to use, often delivering results within 24–48 hours. Many detect coliform bacteria, including E. coli, and some even test for a broader range of contaminants. You can find them online through retailers like Amazon, at home improvement stores such as The Home Depot, or through specialized suppliers like Bio-Rad for more advanced testing needs. Including a few of these kits with your water purification supplies ensures you will know what purification treatments, if any, are needed.

Check Out the Tap Water Database

This will show you what pollutants are presently found in your water supply and the source of each. It will give you advice on choosing a filter that will filter out each contaminant found. Simply enter your zip code to view a report on your local utility.

See Database