Drinking Water, DIY Water Disinfection, Filtration, Desalinization, Collection, SODIS, etc

February 11, 2013 in Water

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Clean water is one of the most basic living requirements for humans on the planet Earth. But for people in many parts of the world it can be a difficult thing to obtain. This article will go over some of the basic do-it-yourself methods to filter, purify, and disinfect, potentially dangerous water, and also to desalinate saltwater if saltwater is all that’s available.

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DIY Water Filtration/Purification

The primary purpose of water filtration is to clean water of debris/turbidity to the point that it can then be further disinfected using other methods, or used as is, if need be (though that’s not preferable for most water uses/sources).

Effective methods of water filtration have been around for a very long time, probably far back into prehistory. Many of the most-ancient but still-known methods, will seem very familiar: sand filters, charcoal filters, seeds and husks of certain plants, stills, etc.

The most basic and easy to create of these, and the method that I will focus on, is a simple grass/sand/charcoal filter. This will work to effectively filter out grit and to remove the turbidity of water, allowing it to be further disinfected with other methods.

All you will need is grass/grain husks, sand, charcoal, some fabrics to hold the materials, and some posts to hang them from. First setup three posts like a tripod, tying them together at their meeting point. Then tie three cloths to the posts, one over the other, over the other. Each of these cloth layers will hold one of the filtering mediums. The top will be grass or grain husks, which can be easily replaced once dirty while still preserving the other layers. The one below will be sand. And the bottom layer will be charcoal, which you can make yourself fairly easily.

And then you simply place your water collection device underneath, and pour the water into the grass layer allowing it to filter through all three.

After this you will still need to disinfect the water, via boiling, SODIS, or other methods. And there are of course more permanent versions of this that could be constructed for those so inclined. It’s a very effective method for most purposes, but is not effective enough to deal with water that is heavily contaminated with toxic chemicals or heavy metals. So sourcing your water from generally clean sources is still preferable.

Another very effective method, the BioSand method, is also a choice, but it requires quite a bit more work. “BioSand filters are a point of use filtration system, developed from slow sand filters, which remove pathogens and suspended solids from water. As compared to other point of use systems, such as chlorination or solar disinfection, BSFs are easier to operate, and less expensive, which makes them a good alternative, especially in developing countries.” DIY BioSand filters will be the subject of a future post.

DIY Water Disinfection

The two simplest and cheapest ways to disinfect water are boiling, and solar water disinfection (SODIS). By raising the temperature of water past the boiling point and keeping it there for over three minutes most disease causing organisms will be killed, all you have to do is wait for the water to cool.

One of the other ways that you can simply and cheaply disinfect water is with the SODIS method, also known as solar ultraviolet water disinfection. All that you’ll need for this method is sunlight and plastic PET bottles (though most types of glass bottles will also work).

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The method is very simple:

1. Clear, colorless PET (plastic #1) bottles (2 liter or smaller size) that are in good condition are located. Water and soda bottles usually fit this description. The bottles are then cleaned and have their labels removed.

2. The water that needs to be disinfected is then poured into the bottles. The bottles should be filled to about 3/4 full, and then vigorously shaken for 20 seconds (capped) to improve oxygen saturation. Then filled completely with more water, and recapped. The water needs to be relatively clear or the method won’t work. Water with turbidity higher than 30 NTU needs to be filtered first.

3. The water-filled bottles are then placed somewhere with good sun-exposure, such as a sloped corrugated roof. The bottles should be placed at an incline, like those of most roofs, if they are left standing straight upwards they will not get enough sun.

4. Depending on the level of sun exposure, the water is clean to drink directly from the bottle. By transferring the water, the risk of recontamination is increased. In most sunny conditions 6 hours is sufficient, in cloudier weather (50-100% cloudy, no rain) it should be left out for a minimum of two days. With rainfall, and very dark conditions, the method is ineffective.

The method works thanks to a combination of synergistic effects:
“UV-A interferes directly with the metabolism and destroys cell structures of bacteria.”
“UV-A (wavelength 320–400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) that are believed to also damage pathogens.”
“Cumulative solar energy (including the infrared radiation component) heats the water. If the water temperatures rises above 50 °C (122 °F), the disinfection process is three times faster.”
“At a water temperature of about 30 °C (86 °F), a threshold solar irradiance of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350–450 nm, corresponding to about 6 hours of mid-latitude (European) midday summer sunshine.”
“At water temperatures higher than 45 °C (113 °F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.”

It’s important to note that the method does not remove heavy metals or toxic chemicals, so a source of water free from these contaminants is important to find, or a more comprehensive water filtering method should be used.

DIY Water Desalinization

The simplest way to desalinate your own water is through the creation of a basic solar still.

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A basic solar still is simply a method of using heat from the Sun to evaporate water from humid soil, or other sources, that is then trapped by a layer of glass or plastic that the sunlight is passing through. An example would be wrapping and tying a clear plastic bag around a branch of a tree, effectively trapping the moisture that would typically evaporate into the atmosphere from the leaves.

For the purpose of desalination, all one has to do is replace the humid soil with saltwater. The method is relatively effective, but depending on the region and climate may require a large setup to supply all of your necessary water.

Because of the simplicity of the method, and freedom of design, there isn’t much to explain. All you need is a transparent material (glass or plastic), some water source that you want to distill (saltwater, soil, urine, foliage), and something to redirect the condensed water (typically an incline in a layer of plastic).

Source: Wikipedia

Image Credits: Still, SODIS, and Water Droplets, via Wikimedia Commons

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