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==Purification methods== | ==Purification methods== | ||
# | Purification is conducted in 1 or 2 or 3 stages, depending on the situation - what is needed, and what is possible. | ||
#Sedimentation. If it is possible to let the water sit for a period of time, or pass slowly through a tank, heavier particles can settle out. (See {{WP|Sedimentation (water treatment)}}.) If the water is relatively clear, this step may not be important. Or if the water is turbid (cloudy) but the solids do not settle out easily, this step may be of little use. It may also be impractical when water is being collected in vessels and carried home - though by leaving the vessels to stand, and not shaking them excessively when pouring, the vessels themselves act as sedimentation tanks. | |||
#Filtering. This is sometimes skipped if the water is very clear. This is important as pathogens and other contaminants are mostly attached to particles in the water. | |||
#*On a very small scale, this may be done with a {{WP|cloth filter}}. | #*On a very small scale, this may be done with a {{WP|cloth filter}}. | ||
#*On a small scale, a small sand filter can be easily built using a bucket, sand and preferably gravel as well. | #*On a small scale, a small sand filter can be easily built using a bucket, sand and preferably gravel as well. | ||
# | #Disinfection. While filtration will greatly reduce the danger of the water, it is still possible for very clear water to contain high levels of pathogens. Disinfection is important to ensure safety, both in killing pathogens, and providing a residual to kill any pathogens which are introduced to the water in the following minutes or hours. | ||
#*Chlorine or iodine tablets. A disadvantage is that people don't like the taste (particularly those not used to chlorinated municipal water supplies) and may fail to treat their water, or react with hostility to those who try to treat the water.<ref>Les Roberts, lecture 5 or 6 (on Rwanda), [http://ocw.jhsph.edu/courses/watersanitation/ Water and Sanitation Needs in Complex Humanitarian Emergencies], in the Global Health course of the Johns Hopkins Bloomberg School of Public Health, available as OpenCourseWare (OCW).</ref> | |||
#* | #*Chlorine bleach is effective and can be used in emergency situations. A few drops of bleach are added to water and left to stand, covered, for a period of time. (How much bleach, and how long should it stand for?{{sp}} Is oxygen bleach effective?{{sp}}) | ||
#* | #*Add a lemon for every liter of water. This reduces the pH of the water which is particularly suitable where [[cholera]] is a potential problem.<ref>"...cholera survives far, far better at high pH than at low pH. In fact, in a few outbreaks [of cholera] in the 90s, the Centers for Disease Control was advocating that people put a lemon per liter in their water. Lowers the pH down to around 4 point something.That's roughly as good as chlorine at killing off vibrios [i.e. cholera]. Incredibly effective." Les Roberts, lecture 5 or 6 (on Rwanda), [http://ocw.jhsph.edu/courses/watersanitation/ Water and Sanitation Needs in Complex Humanitarian Emergencies], in the Global Health course of the Johns Hopkins Bloomberg School of Public Health, available as OpenCourseWare (OCW). (Quote occurs at 13 min 45 sec ion the MP3 file.)</ref> (How effective is it against other pathogens? Is it a viable long-term solution, either at this level or more dilute?{{suggested project}}) | ||
#*{{WP|Slow sand filters}} contribute to disinfection, as well as filtering the water - they clean the water so effectively that even free-floating are removed (though additional chlorination is frequently used). On a large scale, slow sand filters are suitable where there is sufficient land area. Note that slow sand filters may be much more space efficient with suitable management, tilling the sand rather than scraping it, for maintenance. | |||
#*If {{WP|clay pot filters}} or {{WP|Ceramic water filters}} are used, they can be coated inside and out with a silver compound, which acts as a disinfecting agent. (What is the additional cost of the silver coating?{{sp}} What is the effectiveness of the disinfection, compared to an uncoated filter?{{sp}}) | |||
===Removing arsenic=== | |||
In cases of arsenic contamination (discussed in previous section) these measures are not effective. An appropriate technology solution to arsenic is available in the {{WP|Sono arsenic filter}}. As it contains sand and charcoal, the filter should also be effective against other impurities. The water being treated is groundwater and thus should not usually contain significant pathogens - though of course this cannot be guaranteed! | |||
==Protection of water== | ==Protection of water== | ||
Revision as of 11:04, 26 February 2007
Template:Wikipedia p (Insert large disclaimer here.)
This is provided for information only. Appropedia cannot be liable for wrong advice or misinterpretation of advice.
Accessing the water
If a clear source of water such as rainwater, springwater or groundwater is used, this reduces the need for treatment. Surface water (rivers, lakes or ponds) is more likely to be contaminated.
However, in some circumstances the more contaminated source may be worth considering, if it is substantially closer or cheaper (though this argument may be controversial). The lower cost and/or effort would provide a great benefit to those struggling in poverty - in fact it may be the only option for those in extreme poverty. In this case, however, it is essential that the water is reliably treated to a high standard, otherwise the saved expense could be outweighed by medical expenses, and the saved effort outweighed by time and income lost due to illness, not to mention the suffering and potential loss of life.
Questions to ask are addressed in the following subsections.
Is the water currently carried long distances?
Is piping an option? What type of pipe? Consider expense and reliability. E.g:
- Unplasticized W[1] is good for water quality, but very brittle and should not be used unless it can be laid properly, in suitable sand;[2]
- W pipe is more flexible and tougher, but more expensive.
- Bamboo can be used as pipe, but has problems.[verification needed]
Is it carried long distances over very flat land? Consider the W to ease the burden.
Look for other options which don't require the expense of piping or the burden of carrying water daily. (Consider ideas on this page and pages in the category, below; research more widely, and very importantly, consider the local situation and discuss with locals - see Community participation.)
Is there significant rain?
Consider rainwater harvesting. This requires an appropriate method of storage, especially in areas with significant dry seasons.
Is there significant fog?
Consider W. Suitable for areas which experience fog even when there is little rain. It might be speculated that this would not be as clean as groundwater, as the fog might collect dust and other pollutants from the atmosphere.[verification needed]
Is there accessible groundwater?
W may be relatively expensive, but often provide high quality water requiring little or no further treatment, with less travel time than surface water sources.
If using groundwater, check for arsenic, or at least do a proper analysis of the likelihood of arsenic contamination. The local geography and depth should give an indication. Arsenic contamination usually occurs when the water has spent many years underground in certain types of soil - for example, seeping from the Himalayas towards the Ganges delta, over thousands of years. Thus it seems unlikely that arsenic contamination would occur on a small island, for example. See the Wikipedia article W for more. Keep it in perspective as well - fecal contamination is far more deadly and more a far more urgent problem than the levels of arsenic contamination normally found in groundwater, which typically have an effect over years of consumption.
Also consider pollution of the groundwater through agricultural, industrial, or sewage effluent. Sewage is likely to be a problem especially where the groundwater level is near the surface and septic tanks are used.
Is a pump required?
For pumping the water:
- Handpumps and treadle pumps are generally more appropriate to developing world contexts than motor-driven pumps. However, even handpumps are often a problem, failing and left unused due to lack of maintenance. The principle of W is important with handpumps, but may be difficult in application.
- The W uses the energy of children at play to pump water - it is quite expensive, but in some cases has been paid for through advertising displayed at the site.
- Solar pump mills[3] have also been used, especially for agriculture and cases where the water does not have to be on demand. The water simply pumps whenever the sun shines.
Purification methods
Purification is conducted in 1 or 2 or 3 stages, depending on the situation - what is needed, and what is possible.
- Sedimentation. If it is possible to let the water sit for a period of time, or pass slowly through a tank, heavier particles can settle out. (See W.) If the water is relatively clear, this step may not be important. Or if the water is turbid (cloudy) but the solids do not settle out easily, this step may be of little use. It may also be impractical when water is being collected in vessels and carried home - though by leaving the vessels to stand, and not shaking them excessively when pouring, the vessels themselves act as sedimentation tanks.
- Filtering. This is sometimes skipped if the water is very clear. This is important as pathogens and other contaminants are mostly attached to particles in the water.
- On a very small scale, this may be done with a W.
- On a small scale, a small sand filter can be easily built using a bucket, sand and preferably gravel as well.
- Disinfection. While filtration will greatly reduce the danger of the water, it is still possible for very clear water to contain high levels of pathogens. Disinfection is important to ensure safety, both in killing pathogens, and providing a residual to kill any pathogens which are introduced to the water in the following minutes or hours.
- Chlorine or iodine tablets. A disadvantage is that people don't like the taste (particularly those not used to chlorinated municipal water supplies) and may fail to treat their water, or react with hostility to those who try to treat the water.[4]
- Chlorine bleach is effective and can be used in emergency situations. A few drops of bleach are added to water and left to stand, covered, for a period of time. (How much bleach, and how long should it stand for?[expansion needed] Is oxygen bleach effective?[expansion needed])
- Add a lemon for every liter of water. This reduces the pH of the water which is particularly suitable where cholera is a potential problem.[5] (How effective is it against other pathogens? Is it a viable long-term solution, either at this level or more dilute?[expansion needed])
- W contribute to disinfection, as well as filtering the water - they clean the water so effectively that even free-floating are removed (though additional chlorination is frequently used). On a large scale, slow sand filters are suitable where there is sufficient land area. Note that slow sand filters may be much more space efficient with suitable management, tilling the sand rather than scraping it, for maintenance.
- If W or W are used, they can be coated inside and out with a silver compound, which acts as a disinfecting agent. (What is the additional cost of the silver coating?[expansion needed] What is the effectiveness of the disinfection, compared to an uncoated filter?[expansion needed])
Removing arsenic
In cases of arsenic contamination (discussed in previous section) these measures are not effective. An appropriate technology solution to arsenic is available in the W. As it contains sand and charcoal, the filter should also be effective against other impurities. The water being treated is groundwater and thus should not usually contain significant pathogens - though of course this cannot be guaranteed!
Protection of water
Water storage containers:
- lids
- mosquito netting over any opening, with no holes in the netting. Also for septic tanks.
Water sources (W).
Footnotes
- ↑ PVC is sometimes regarded as a toxic plastic; most or all of the problems for the end user result from the plasticizers. See discussion in comments at Go PVC Free (Green Options) (but better sources than this are needed)[verification needed]
- ↑ A water consultant told of his experience in Indonesia, where he found that local workers had begun to lay the brittle PVC pipe in gravel, which would have led to a very short effective life-expectancy for the pipe. When he asked why they hadn't followed instructions, they said "We didn't have sand, so we used gravel." - Personal conversation with Chriswaterguy. A more appropriate response, of course, would have been to wait for the sand or seek instructions for the supervising engineer. Thus an understanding of the culture, and appropriate supervision by a qualified person are very important.
- ↑ Solar energy systems http://www.sesltd.com.au
- ↑ Les Roberts, lecture 5 or 6 (on Rwanda), Water and Sanitation Needs in Complex Humanitarian Emergencies, in the Global Health course of the Johns Hopkins Bloomberg School of Public Health, available as OpenCourseWare (OCW).
- ↑ "...cholera survives far, far better at high pH than at low pH. In fact, in a few outbreaks [of cholera] in the 90s, the Centers for Disease Control was advocating that people put a lemon per liter in their water. Lowers the pH down to around 4 point something.That's roughly as good as chlorine at killing off vibrios [i.e. cholera]. Incredibly effective." Les Roberts, lecture 5 or 6 (on Rwanda), Water and Sanitation Needs in Complex Humanitarian Emergencies, in the Global Health course of the Johns Hopkins Bloomberg School of Public Health, available as OpenCourseWare (OCW). (Quote occurs at 13 min 45 sec ion the MP3 file.)