Guide to Filtering Water
A Guide to Water Filters
Many but not all available home water filters remove Cryptosporidium. Some filter designs are more suitable for removal of Cryptosporidium than others. Filters that have the words "reverse osmosis" on the label protect against Cryptosporidium. Some other types of filters that function by micro-straining also work. Look for a filter that has a pore size of 1 micron or less. This will remove microbes 1 micron or greater in diameter (Cryptosporidium, Giardia). There are two types of these filters — "absolute 1 micron" filters and "nominal 1 micron" filters but not all filters that are supposed to remove objects 1 micron or larger from water are the same.
- The absolute 1 micron filter will more consistently remove Cryptosporidium than a nominal filter.
- Some nominal 1 micron filters will allow 20% to 30% of 1 micron particles (like Cryptosporidium) to pass through.
- the NSF trademark on Tested and certified by NSF Standard 53 or NSF Standard 58 filter plus the words "cyst reduction" or "cyst removal" on the product label information.
- Reverse osmosis (with or without NSF testing)
- Absolute pore size of 1 micron or smaller (with or without NSF testing)
- You can also contact the NSF at 789 N. Dixboro Road, Ann Arbor, MI 48113 USA, toll free 800-673-8010 or 888-99-SAFER, fax 734-769-0109, email email@example.com, or visit their Web site at www.nsf.org/certified/DWTU/. At their Web site, you can enter the model number of the unit you intend to buy to see if it is on their certified list, or you can look under the section entitled "Reduction claims for drinking water treatment units - Health Effects" and check the box in front of the words "Cyst Reduction." This will display a list of filters tested for their ability to remove Cryptosporidium.
- Because NSF testing is expensive and voluntary, some filters that may work against Cryptosporidium have not been NSF-tested. If you chose to use a product not NSF-certified, select those technologies more likely to reduce Cryptosporidium, including filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller.
- Treating water with chlorine tablets, iodine tablets, or liquid bleach WILL NOT kill all parasites that can contaminate water; boiling or appropriate filtration is required.
Guide to Storing Water
A preparedness supply kit should include one gallon of drinking water per day per person.
What to store water in:
You can store water in food grade plastic or glass containers with tight fitting screw-on caps.
- Food-grade containers include those that previously held beverages, such as 2-liter soda bottles and other water, juice, or punch containers. Plastic milk bottles should be avoided, because it is difficult to remove protein and fat residues, which may allow bacteria to grow during storage.
- You can buy new plastic containers for water storage in most housewares and sporting goods departments, and clean food-grade containers may be available for purchase at water vending machines. Only purchase containers labeled for storage of food or beverages. Containers not labeled for food or beverage storage could release harmful chemicals into the water. Never use a container that has held toxic substances, because tiny amounts may remain in the container's pores. Some plastic containers may affect the taste of stored water. Avoid using containers that will decompose or break, such as milk cartons or glass bottles. Also, some old glass jars were made with glass that contains lead, and unacceptable amounts of lead can leach into water stored in them even for short periods.
How should I treat the water for storage?
Be sure that the water you are treating is drinking-quality water to begin with. To treat water for storage, use liquid household chlorine bleach that contains 5.25 percent sodium hypochlorite. Do not use bleach with soaps or scents added. Add the bleach according to the list below, using a clean, uncontaminated medicine dropper.
4 drops bleach per quart or liter container of water
8 drops bleach per 2-quart, 2-liter, or ½ gallon container of water
16 drops bleach, or 1/4 teaspoon, per gallon or 4-liter container of water
When treating larger quantities of water, use the following table to convert drops to standard measuring units.
8 drops = 1/8 teaspoon
16 drops = 1/4 teaspoon
32 drops = ½ teaspoon
64 drops = 1 teaspoon
192 drops = 1 Tablespoon
384 drops = 1/8 cup which is = 2 Tablespoons
- Water stored in metal containers should not be treated, prior to storage, with chlorine since the chlorine compound is corrosive to most metals. Therefore, only very pure water should be stored in metal containers.
- Do not boil water before storing it. It will not prevent all problems that may occur during storage. In addition, boiling may concentrate other contaminants as the water evaporates away.
- Store containers in a cool, dry place away from direct sunlight. Because most plastic beverage containers degrade over time, store them away from heat and light to prevent leakage. Because hydrocarbon vapors can penetrate polyethylene plastics, store water in plastic containers away from gasoline, kerosene, pesticides, or similar substances.
- Water weighing over 8 pounds per gallon. Make sure the shelves or area in which you store the water is strong enough to support the weight.
- For best quality, replace water stored from a public, or vended water supply every 6 months.
- For commercially bottled distilled or drinking water, check the label for an expiration date. If none is given, bottled water with the IBWA or NSF seal should have a shelf-life of at least one year.
- You can also store water for an extended period of time in the freezer. If you lose electricity, the frozen water will help keep foods in the freezer frozen. Leave 2 to 3 inches of air space in the top of containers before freezing, to keep the container from breaking as water expands during freezing. Some glass containers may break regardless of the air space provided.
- To improve the taste of water stored for a long time, pour it from one clean container to another clean container several times, to put air back into it.