Gravity flow water filter

This gravity flow water filter will remove giardia, cryptosporidian and many other pathogens from the water. The core is activated charcoal, which will remove chlorine, heavy metals, and toxic organic chemicals. Water should be disinfected after it is filtered (see below). Use the cleanest source of water available. If the only available water source is cloudy, filter it first through a coffee filter or cloth. Find a very clean container to receive the water. Sterilize the container with chlorine bleach. Rinse out all of the chlorine. The filter works by gravity. The level of water in the source container must be higher than the water level in the receiving container, or there will be no flow. The filter works slowly. A large source container and a large receiving container allows filtration to occur with less attention. Assemble the filter by placing the tube through the nipple, part 3. Place part 2 into the end of the tube. Screw three onto 4 and 4 onto the filter, 5.

Easy way: Throw this into a source water bucket and put the end of the tube into the sterile container for drinking water.

Better: Drill a hole in the side of the source water bucket near the bottom. Place the rubber gasket on the filter nipple and push the nipple through the bucket side. Assemble as above and screw on part 4 on the outside wall of the source bucket.

When the ceramic is clogged, the flow of water will slow. Take the filter into another pail of clean water. Use a clean toothbrush to gently brush the sides of the white ceramic to remove particles. Rinse the filter and return it to the source bucket.

Solar Disinfection(1)

At its simplest ("batch-process" solar disinfection), the method involves filling a transparent plastic or glass vessel with contaminated water and then keeping this vessel in full-strength sunlight for several hours, to inactivate pathogenic microbes. Using discarded plastic (PET) drinks bottles in laboratory and field experiments, research has demonstrated that solar radiation can inactivate a wide range of microbes, including fecal indicator bacteria such as E. coli, waterborne pathogenic bacteria such as those responsible for cholera and dysentery, and certain viruses and protozoal parasites. Continuous-flow solar water treatment systems have also been developed and evaluated, though these are more complex and sophisticated in design and operation (for a more detailed review of solar water treatment, see Reed 2004).

Solar disinfection is the result of two processes:

1. thermal inactivation: absorption of solar infrared radiation can raise the temperature of illuminated water to the point where microbes are inactivated, as a result of thermal damage to heat-sensitive biological structures such as membranes. When this is carried out in a black-painted container or in a solar cooker, it is often termed "solar pasteurization," by analogy with commercial pasteurization. However, such temperatures are not always readily achieved during solar water treatment in a transparent bottle, especially outside the summer season.
2. optical inactivation: ultraviolet and visible wavelengths of sunlight may be absorbed by photosensitizer molecules, found either within microbial cells (e.g. porphyrins and other pigments), or in the surrounding water (e.g. humic substances). The excited photosensitizer will then usually react with molecular oxygen, leading to the production of various reactive oxygen species including superoxide and hydrogen peroxide. These reactive oxygen species then interact with the macromolecular constituents of microbial cells, causing irreversible inactivation ("solar photo-oxidative disinfection").

It is generally accepted that optical inactivation due to solar UV radiation is the main component of solar disinfection. However, research has shown a synergistic interaction between optical and thermal inactivation at temperatures above 45°C (~113°F), where the combined optical and thermal effects act to inactivate bacteria at a faster rate than would be predicted from the effect of each factor in isolation (Reed 2004).

Since the optical inactivation process involves the sunlight-driven production of reactive oxygen species, solar disinfection is strongly influenced by the level of dissolved oxygen in the water, being optimum only under oxygen-saturated conditions; however, this is relatively easily achieved by leaving a small air gap during filling, and then shaking the bottle (Reed 1997).

The optical inactivation process is also sensitive to water turbidity, being most effective with water of low-to-moderate turbidity (typically up to100 turbidity units). For water of higher turbidity, a three-stage process can be used:

1. Clarification - by sedimentation, filtration or coagulation/flocculation (in Rajasthan, the villagers sometimes add dried sand, known locally as "balu mitti," to reduce the turbidity of water with a high level of suspended solids before use).
2. Oxygenation - by vigorous mixing of the container before exposure to sunlight.
3. Illumination - in full-strength sunlight, for as long as possible (ideally, a whole day).

(1) http://ag.arizona.edu/OALS/ALN/aln57/reed.html

Chemical treatments(2)

Chlorine and iodine are the most commonly used chemicals for emergency disinfection of water. The killing effectiveness of the chemical depends on the concentration of the chemical in the water, the amount of time the available chemical is in contact with the water prior to use (contact time), the water temperature and the characteristics of the water supply. A decreased concentration of the disinfectant or a lower temperature will require a longer contact time for adequate disinfection. If the water temperature is less than 41ºF (or 5ºC), it should be allowed to warm prior to disinfection or the chemical dose should be doubled. If the water is cloudy, it is recommended to strain it through a coffee filter before treatment.

A common objection to chemical disinfection is the flavor it gives to the treated water. If flavorings of any kind are added to the water to improve taste it should be done after the recommended contact time for disinfection. Flavorings added before adequate contact time has been achieved will "tie up" some of the chemical available for disinfection. Adding about 50 mg of vitamin C (ascorbic acid) per liter or quart of water after the contact time can improve the taste. Vitamin C is often available in 250 and 500 mg tablets where vitamin supplements are sold. Tablets should be pulverized and divided before adding to the water. In addition, freshness preservatives containing vitamin C are often available where canning supplies are sold.

Bacteria are very sensitive to chemical disinfectants such as chlorine and iodine. Viruses, cryptosporidium, and giardia require very high dosages of disinfectant or longer contact times with the disinfectant than the standard recommendations. Heat treatment is recommended if these pathogens are suspected in the water.

Chlorine. Regular household chlorine bleach that contains 5% to 6% sodium hypochlorite as the only active ingredient can be used for disinfection. Standard household bleaches are 5.25% sodium hypochlorite; those labeled "Ultra" are generally 6% sodium hypochlorite. Bleaches with labels such as "Fresh Wildflowers," "Rain Clean," "Advantage," or labeled as scented may contain fragrances, soaps, surfactants, or other additives and should be avoided for drinking water disinfection. Using a medicine dropper, add 16 drops per gallon (4 drops per quart). Stir the water and let it stand covered for 30 minutes. For adequate disinfection, the water should have a slight chlorine odor to it after the 30 minute waiting period. If this odor is not present after the 30 minutes, repeat the dose and let it stand covered another 15 minutes. If this odor is not present, the bleach may have lost its effectiveness due to age of the product or exposure to light or heat.

Use the freshest chlorine bleach available. If the chlorine taste is too strong in the treated water, taste can be improved by pouring the water from one clean container to another several times.

Iodine. Two forms of iodine commonly sold for chemical disinfection of drinking water are tincture of iodine (2%) and tetraglycine hydroperiodide tablets (Globaline®, Coghlan's® and Potable-Aqua® are examples). Iodine was once widely used, but is no longer recommended because health research has shown that as many as 8% of people have hidden or chronic thyroid, liver, or kidney disease which iodine can make worse. Iodine should not be ingested by children younger than age 14. Do not use iodine-containing products unless you have discussed the risks with your physician.

(2) http://ianrpubs.unl.edu/water/g1494.htm

Ceramic Filter Specifications

Additional information from Michael at Step by Step Farm

0.9 microns EFFECTIVE is rather coarse for a decent water filter. You should shoot for 0.4-0.5 microns absolute (0.1 -0.2 micros effective) which will exclude the larger viruses.

For emergency use where the water bourne viruses like Hepatitis A need to be considered, ceramic filters are unsuited to amateur use because they must be handled to clean them (whoever does THAT should be "suited up" as they would be exposed to HIGH concentrations as the gunk being scraped off with that toothbrush spatters into the air). Better in this case to use canister type filters which are cleaned by "backflushing".

DON'T spend too much for an improvised unit. A "First Need" cannister (a component of a clumsy but effective hiking filter) is probably less than $50 (I haven't bought one recently) and these are quite easy to use as gravity filters. When caretaking at Upper Goose Pond Cabin (on the Appalachian Trail) I use an old clogged cannister is a gravity filter setup between two 5 ga collapsibles and enough tubing to rig them at 8' head. It easily delivers ~1/2 ga/hour. A NEW cannister of this type is 0.4 micros absolute (effective 0.1-0.2 microns) but of course my old clogged cannister is probably now much finer than that. The point here is a "First Need" cannister, a pair of 5 ga collapsibles, a gas line filter (pre filter) and enough tubing to connect them -- nesting sizes to work up to the diameter of the collapsible jug tube, a few hose clamps to keep the tubing tight -- it would total well under $100 and should deliver about 1 ga/hour at reasonable head << need to backflush every 10-20 gallons and probable capacity till HOPELESSLY clogged a few hundred gallons ---- after about 100 gallons they are too clogged for use hiking (would need to pump too slow to be practical) but here the delivery rate just gradually slows down.

http://www.generalecology.com/

They of course make large units such as would be used by RVs or boats and since not all sailboats have auxillary power at least some Seagull IV units have manual pumps. But Seagull IV is probably about $500 and their replacement filters ~$100. You could check with their tech people whether the cannisters could be used as gravity filters without the expensive stainless steel casing the way the small hiking filter cannisters can be used without the pump.

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