Identifying & Treating Unsafe Water

Water Purification

We must be ready to treat unsafe water from our home faucets and non-potable water from outside sources should the need ever arise. Preparing for these two possibilites 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 the term "contaminant" as meaning any physical, chemical, biological, or radiological substance or matter in water. Most cause harm when ingested, not absorbed.

Water Purification
General Categories of Drinking Water Contaminants


Physical contaminants primarily impact the physical appearance and properties of water. They make water unappetizing and dirty, but they won’t harm you if swallowed. Examples are sediment or organic material suspended in the water of lakes, rivers and streams.

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


Chemical contaminants are both naturally occurring and man-made. Natural pollutants are often byproducts of runoff, erosion, or organisms within water. Man-made contaminants appear due to spills, disposal & application methods, and erosion of metals used in water pipes.

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 contaminants are microorganisms living in water and include viruses, bacteria, and parasites. You cannot see them with the naked eye, so testing water is vital as exposure can make you very sick. Even trace amounts cause vomiting and diarrhea. Microbes are responsible for causing E.coli, Salmonella, Hepatitis, Giardia, Cryptosporidium cholera, typhoid, worm infections, and many other waterborne illnesses.

Effective against parasites, bacteria, and viruses
Reverse Osmosis
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


Many radiological contaminants found in public drinking water occur naturally. For example, radioactive radium and uranium are found in small amounts in almost all rock and soil and can dissolve in water. Other radiological contaminants are man-made and are brought about by improper disposal of radiological wastes and broken reactors. Nuclear fallout can also pollute a water supply.

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

Signs of unsafe water

Contaminated water can have a bad odor and taste. It can contain microorganisms such as germs, bacteria, and viruses that can cause dysentery, typhoid, and hepatitis.

Treating water contamination

If your water supply is not known to be safe or if there is any doubt about its quality, the water should be purified before using it for drinking, washing dishes, brushing teeth, washing and preparing food and baby formula, or hygiene. Once identified, purification methods can be employed. This is a two-step process: debris removal & pathogen removal.

Step 1: Debris removal

Debris removal occurs when the contaminants that are causing your water to be dirty or cloudy are filtered out. Though you can use layers of a paper towel or a coffee filter, your best bet is to use a water filter. Learn more below.

Step 2: Pathogen removal

Pathogens like protozoa, bacteria, and viruses must be removed or killed. Some methods are capable of killing all three at one time, while others need to be used together in order to successfully purify the infected water. Learn more below.

Water Purification
Debris Removal

Sediment filtration

Debris removal is done through the filtration process. Filters come with different pore sizes that are measured in microns. If the contaminant is larger than the micron size of the filter, it will be caught and filtered out. 5-micron sediment filters are the most common type of micron filter. This filter type will catch any dirt and debris that is larger than 5 microns. Anything smaller will pass through.

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

Water Purification
Pathogen Removal

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 method do. It is ineffective at removing toxins.


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.
  • Keep in mind that some water will evaporate.
  • Let the water cool before drinking.

Tips for better tasting water

Boiled water will taste better if you do one of two things - you don't have to do both.

  • Pour the water back and forth between two clean containers and then allowing it to stand for a few hours. This allows oxygen into the water which improves taste. (You can also use this method for stored water as well, though you don't need to wait the few hours.)
  • Add a pinch of salt for each quart or liter of boiled water.

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Chemical Disinfection

Chemical disinfectants kill viruses and bacteria, and the giardia parasite. They are not effective against the more stubborn cryptosporidium parasite. You can follow this treatment up with a 1-micron filter which will do that for you.

Here are three popular disinfectents: bleach, chlorine dioxide, and iodine - also an alternative that you should always keep in storage: pool shock. A little pool shock goes a long way! See below.

Chlorine Bleach

Typically, unscented liquid chlorine bleach in the United States will be between 6% and 8.25% sodium hypochlorite, though concentrations can be different in other countries. Directions below are for both concentrations - read the label to determine how much bleach you will need to add for proper purification.


  • Choose method of measurement: a dropper, an mL syringe, or a teaspoon set
  • Add the appropriate amount of bleach to your water - see mixing amounts
  • Stir the mixture well.
  • Let it stand for at least 30 minutes before you drink it.
  • Store the disinfected water in clean, sanitized containers with tight covers.

Mixing Amounts

6-8.25% sodium hypochlorite
Per quart or liter
  • Add 2 drops | 0.1 mL | tiny amount*
Per 1 gallon
  • Add 8 drops | 1/2 mL | 1/8 tsp
Per 5 gallons
  • Add 40 drops | 2 1/2 mL | 1/2 tsp
* too small to measure
1% sodium hypochlorite
Per quart or liter
  • Add 10 drops | 1/2 mL | 1/8 tsp
Per 1 gallon
  • Add 40 drops | 2 1/2 mL | 1/2 tsp
Per 5 gallons
  • Add 200 drops | 12 1/2 mL | 2 1/2 tsp

For easier measuring follow these tips:

  • Don't use a teaspoon to measure bleach when treating a quart/liter or less. Other methods are more reliable.
  • Store your measuring devices with your bleach so it's there when you need it.

- place with your storage materials -

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

Most of the time, one tablet can purify 1-2 liters of water in 30 minutes.

  • Fast acting
  • Is a popular method for on-the-go water disinfection
  • the pre-portioned tablets are easy to use and safe as long as you follow the instructions on the packet.
  • Does not have a bad taste or smell.

Shelf life is 4 years from date of manufacture.


Iodine (common household or tincture) is a chemical element and a stable halogen. It is used as a moderately effective disinfectant.

Liquid 2% Solution

Add five drops of iodine to each quart or liter of water that you are disinfecting. If the water is cloudy or colored, add 10 drops of iodine. Stir and let the water stand for at least 30 minutes before use.

Tablet (tetraglycine hydroperiodide)

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

  • It is the least expensive of the two forms of tablets (comparing it with Chlorine Dioxide)
  • It doesn't taste very good so you may want to add some form of powdered drink to the water when using it.
  • It's NOT recommended for pregnant women, people with thyroid problems, or those with known hypersensitivity to iodine.
  • It’s not recommended for continuous use—don’t use it for more than a few weeks at a time.

Shelf life is 4 years from the date of manufacture.

Pool Shock

Pool shock is a chlorine-based product used for swimming pools. If used carefully and correctly, the EPA has stated that you can use it to disinfect your water supply just as you would bleach. It is a strong chemical so care needs to be taken and really 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 if stored properly (see below). A 1-pound bag can disinfect 10,000 gallons of water. 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 that contains 68% or higher Calcium Hypochlorite. Brand examples include: HTH Ultimate–Shock Treatment 7 in 1 and Ultima TKO.

- place with your storage materials -

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Filtering of Pathogens

Filtration for pathogen removal purposes must be done with a filter that is 90 times smaller than human hair and 40 times smaller than a grain of sand. Only filters rated 1 micron can remove parasites (including the hardest to get rid of crypto/cysts), heavy metals, pesticides, and herbicides. It cannot remove viruses and bacteria. Boiling or the use of disinfectants can do that.

Whether you are purchasing a filter for your home (point of entry) or a portable filter (point of use), always look for one that has a 1-micron rating. Then, decide if proof of certification is important.

Here is a good (and short) explanation on what micron filters are.


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 1-micron 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 1-micron 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 Crytpo 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 The bottles must be made of PET plastic or glass (a 2-liter soda bottle is okay).
  • #3 The bottles must be in good condition, washed, colorless and transparent, and label-free.
  • #4 Fill the bottles with water and close the cap.
  • #5 Shake the bottles thoroughly to mix the oxygen.
  • #6 Expose the bottles to direct sunlight for at least 6 hours or for 2 full days under cloudy conditions.
  • #7 Store the water inside the treated bottles until you are ready to use them as refilling and storing the treated water in other containers increases the risk of contamination.
  • #8 When desired, drink the treated water directly from the bottle or from a clean cup.

  • This method is relatively easy when comparing it to other methods.
  • This method is inexpensive as you use the materials you already have.
  • You must wait 6 hours to 2 days or have enough water already treated.
  • There must be sufficient sunlight.
  • This method targets only biological contamination. You must use other methods as well for wider purification.

- place with your storage materials -

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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.


UV process

Contaminated water is exposed to germicidal ultraviolet light. The UV wavelength damages the DNA of the 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.

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 chamber, the UV lamp emits a germicidal wavelength of radiation through the glass and on to the water. This deactivates all living organisms.

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.

  • 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.
  • High dosage UV filters can be relatively expensive to purchase.
  • Low dosage 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 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 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, 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
  • Is considered to be one of the purest forms of potable water.
  • Water treated with this method is stripped of important minerals which produces a flat taste.
  • The unit puts out a great deal of heat during its run which can be problematic during hotter months.
  • More affordable lower volume units take a while to produce a meaningful amount of water.
  • Higher volume units are much more expensive.
  • Runs on and requires a great deal of electricity to operate.
  • Because it won't work during a power outage, this method may not be suitable for emergencies or survival needs unless the use of a generator is factored in.
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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 semipermeable membrane, it stops almost anything larger than a water molecule from passing through. The use of sediment and carbon filters are 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 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.

  • Reverse Osmosis is the most effective eliminator of all disease-causing organisms and most chemical contaminants.
  • 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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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.