Water purification is the process of removing or killing the germs, bacteria, and other contaminates in water that can make you sick. Purifying or disinfecting your filtered water can be done by either boiling or treating with a disinfectant. Water should be filtered before it is purified. When possible, multiple approaches should be used on the water.
Not all water can be made safe for use. It is not practical to purify water that is tainted with certain chemicals, minerals, or radioactivity. You are responsible for ensuring that your water is safe to drink.
Purification with heat
Heat is an effective way to kill waterborne pathogens.
Boiling
Boiling is the best way to kill disease-causing organisms, including viruses, bacteria, and parasites. The high temperature and time spent boiling are very important to effectively kill the organisms in the water. Boiling will also effectively treat water if it is still cloudy or murky.
If you’re at an elevation below 6,500 feet, put the water in a container over a heat source, such as a campfire or propane stove, and bring to a rolling boil for 1 minute. If you’re at an elevation over 6,500 feet, bring the water to a rolling boil for 3 minutes.
Your water is now ready for drinking! You can make tea or coffee if you like it hot. Let it cool down first before you put it into your container.
Sub-boiling purification
You can also treat water at temperatures below boiling if necessary. Typical times at temperature:
- 212F (100C, boiling at sea level) - 0 minutes
- 158F (70C) - 1 minute
- 145F (63C) - 30 minutes to achieve pasteurization[1]
- 130F (55C) - 10 minutes to kill giardia[2]
For comparison, milk is pasteurized at 161F for 15 seconds or 145F for 30 minutes.[3] Enteric bacteria, spores, and viruses are killed by sufficient time at 160F.[4] If using boiling as a reference point when you don't have a thermometer, merely bringing the water to the boiling point is sufficient; holding the boil is "excessive".[5] There is nothing magic about boiling.
Given that information, solar ovens or similar devices that can hold 140F-160F for long periods may provide unpowered heat disinfection. Also see solar water disinfection below.
Heat-surviving pathogens
Some pathogens can survive heat treatment, but they are either not found in water, or boiling reduces the pathogens to safe levels:
Sterilization of water (killing all living containments) is not necessary to make water safe to drink. For example, boiling may not be effective against bacterial spores such as Clostridium which can survive at 100°C (212°F), however, as Clostridium is not a waterborne enteric (intestinal) pathogen, ingestion will not cause infection.
All waterborne enteric pathogens are quickly killed above 60°C (140°F), therefore, although boiling is not necessary to make the water safe to drink, the time taken to heat the water to boiling is usually sufficient to reduce pathogens to safe levels. Allowing the boiled water to cool slowly will also extend the exposure of waterborne enteric pathogens to lethal temperatures. Boiling also gives a simple visual indicator that a high enough temperature has been reached when a thermometer is not available.[6]
Disinfection
Disinfection happens when a chemical or UV light is added to water to kill bacteria, viruses, and other potentially harmful organisms. Many factors can impact the effectiveness of these methods including water temperature, pH, and cloudiness. With disinfectants, it is important to allow the chemical or UV light enough time to treat the water and kill the organisms before drinking – this is called contact time.
Chemical disinfection
Chemical disinfection involves adding one or more chemicals to your filtered water that are effective at killing waterborne organisms. Chemical treatments require no power making them especially useful offgrid. Treated water can be run through a charcoal filter (Brita) after treatment to improve flavor. Pouring treated water energetically from container to container may allow chemicals to outgas.
Chemical tablets or liquid drops are the most common ways to disinfect natural water. Iodine or chlorine dioxide are the most frequently used disinfection agents. National Sanitation Foundation (NSF) approved products are recommended. Follow the manufacturer’s instruction for disinfecting the water. Contact time to disinfect the water varies by product (example: 30 minutes to 4 hours). If the water is cloudy or has floating debris, it will be more effective to pre-filter the water before disinfecting.
Bleach
The most famous treatment is chlorine bleach. The "dosage" is:[7]
- 8 drops per gallon of 6% bleach, or
- 6 drops of 8.25% bleach, or
- 1/2 teaspoon per 5-gallon bucket
After adding the bleach, you must wait 30-45 minutes.[8] Note that bleach purification does not reliably kill Cryptosporidium. Increasing wait time to 45mins will kill norovirus and giardia.
Bleach is cheapest by the laundry bottle but is also available as tablets. Unscented "plain" bleach is better than expensive bleach with additives. An eye dropper bottle will store and dispense l1quid bleach accurately.
Iodine tablets
Iodine tablets were popular with hikers in the past but impart a noticeable flavor to the water. Some come with an additional tablet to be used after the waiting period, intended to remove iodine flavor and color from the water. Iodine treatment should be avoided by people with shellfish allergies.[9]
Flocculation
Flocculation means suspended particles are drawn together and either drop out of suspension or (less commonly) float to the top. Hybrid chlorinating-flocculating chemicals such as Flo-Chlor show promise for turbid water, but they are not widespread yet.
UV Light Purifiers
Portable battery-operated UV purifiers can be used to reduce bacteria, viruses and protozoa in water from natural sources. However, these purifiers are only effective in disinfecting small quantities of clear water, are battery dependent and require correct contact time with the water. To achieve maximum disinfection, make sure you: Pre-filter your water as small particles and sediment may shield microorganisms from the UV light. Check that you have enough battery power. If the battery power falls below a certain level, it will not be able to safely disinfect water. Make sure you allow for enough contact time with the water. Follow the manufacturer’s instructions because inadequate exposure to the UV light may fail to disinfect your water. As an extra precaution: Add a small amount of your preferred chemical disinfectant to the water in your container to maintain water quality and reduce the growth of organisms in the container.
Solar Water Disinfection
Solar water disinfection (abbreviated SODIS) uses sunlight to improve water quality.[10] It relies on minimal solar heating of the water, then ultraviolet irradiation in the container. Since UV does not travel far in water, relatively small bottles of 2L or less are used.[11] Bottles should be clean and free of surface scratches. Efficacy: at 86F water temp, ~6 hours of sun (less than 50% cloudy) will significantly reduce diarrhea reduction-causing pathogens in the water. The actual spect is 500w/m2, which is half of the lab spec for solar panel output (1000w/m2) In fully clouded conditions it takes two full days for disinfection to occur. SODIS at normal temperatures might best be thought of as an adjunct method to be used alongside other methods rather than a disinfection method unto itself. Optimal function may be found by placing small-diameter bottles in a solar oven. This will enhance UV collection and heating.
Resources
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| Wikipedia | Wikipedia article on "Water purification". | |
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| Search NomadLife.wiki | Search other pages on this wiki for "water purification" |
Some or all of the content on this page was originally sourced from this page on RVWiki
- ↑ https://www.engineeringtoolbox.com/pasteurization-methods-temperatures-d_1642.html
- ↑ https://www.epa.gov/sites/production/files/2015-10/documents/giardia-factsheet.pdf
- ↑ https://en.wikipedia.org/wiki/Pasteurization#Process
- ↑ https://academic.oup.com/cid/article/34/3/355/388050
- ↑ https://academic.oup.com/cid/article/34/3/355/388050
- ↑ https://academic.oup.com/cid/article/34/3/355/388050
- ↑ https://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water
- ↑ https://worldwaterreserve.com/potable-water/purification/how-to-purify-water-for-drinking/#Disinfection_with_ChlorineBleach
- ↑ https://www.wikihow.com/Purify-Water
- ↑ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1718112/
- ↑ https://en.m.wikipedia.org/wiki/Solar_water_disinfection