Water supply and purification for emergencies
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This page discusses water supply and treatment in emergency situations, and other situations where resources are limited, such as poor, small or remote communities, and communities following a principle of simple living. For larger scale and/or higher technology solutions, see Municipal water supply and purification methods.
Finding or choosing the sourceEdit
If a clear source of water such as rainwater, springwater or groundwater is used, this reduces the need for treatment. Spring water typically doesn't need treatment, unless it is polluted at the outlet. The quality of water at the outlet may be protected with a spring box.W
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.
In many cases, more than one source will need to be considered - typically a high-quality easily accessible source when available (e.g. rain in the rainy season), with a backup for when this water runs out.
Questions to ask are addressed in the following subsections:
Is the water currently carried long distances?Edit
Is piping an option? What type of pipe? Consider expense and reliability. E.g:
- Unplasticized PVCW is good for water quality, but very brittle and should not be used unless it can be laid properly, in suitable sand;
- HDPEW pipe is more flexible and tougher, but more expensive.
- Bamboo can be used as pipe, but is problematic.[verification needed] Because culms of bamboo are segmented, it is necessary to remove the rigid membrane that divides hollow sections. One technique is to cut an opening at each node along one side of the bamboo length and extricate the rigid membrane. With all the nodes cleared, the bamboo has become a continuous length of pipe that can be installed above ground with all the holes facing up. The drawback to this design is that the bamboo pipe cannot be buried or used for pressurized water distribution.
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?Edit
Consider rainwater harvesting. This requires an appropriate method of storage, especially in areas with significant dry seasons.
Is there accessible groundwater?Edit
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 Arsenic contamination of groundwaterW 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. Arsenic concentrations can be reduced with the use of iron and manganese oxides.
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 there significant fog?Edit
Consider fog collectionW. Suitable for areas which experience fog even when there is very little rain. It might be guessed that this would not be as clean as groundwater, as the fog might collect dust and other pollutants from the atmosphere.[verification needed]
Are you lost in a remote place?Edit
Is a pump required?Edit
For pumping the water:
- A pump operating on manual power, such as a handpumpsW or treadle pumpW or hydraulic ramW, is 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 Village Level Operation and MaintenanceW is important with handpumps, but may be difficult in application.
- The roundabout playpumpW 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-powered pumpsW have also been used, especially for agriculture and remote areas (including Western Australia and Eastern Timor). The water is simply pumped whenever the sun shines.
Purification is conducted in 1 or 2 or 3 stages, depending on the situation - what is needed, and what is possible. Multiple methods mentioned here may be used in combination to produce safe drinking water. For example on a small scale, solar water disinfection requires fairly clear water, so a simple method of filtration, such as a basic sand filter may be used first.
- 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 Sedimentation (water treatment)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 (low turbidity). Filtering is usually important as pathogens and other contaminants are mostly attached to particles in the water.
- 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. If no prior filtration was carried out, more aggressive disinfection will likely be needed.
- Boil the water for several minutes. (Varied instructions are often given - boil the water for 20 minutes, or boil for 3-5 minutes. Common practice in some areas is to bring it the boil, switch off, then leave to sit with a lid on. In a tropical climate it will take a long time to cool, and this extended period at near boiling temperature also helps the disinfection process. The most heat-resistant pathogens are amoeba such as giardiaW and cryptosporidiumW, so the longer boiling times are needed to kill these.[verification needed]) Boiling water uses resources and is thus less than ideal - however it is very effective at making water safe to drink.
- Solar water disinfectionW is effective (provided the water is clear before starting) and requires only PET bottles and a black or reflective surface (or paint half bottle black, so the bottom part is black when it lies on its side).
- 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.
- 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?[Suggested project] Is oxygen bleach effective?[Suggested project] Why only emergency situations?[Suggested project])
- 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. (How effective is it against other pathogens? Is it a viable long-term solution, either at this level or more dilute?[Suggested project])
- Slow sand filtersW 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 clay pot filtersW or ceramic water filtersW 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?[Suggested project] What is the effectiveness of the disinfection, compared to an uncoated filter?[Suggested project])
The scale of the water needs, and whether it is to be a centralized or distributed approach, influence the choice of technologies.
For large scale, more sophisticated technologies may become cost effective - although the need for skilled operators may still be a barrier in some contexts. See Municipal water supply and purification methods.
In cases of arsenic contamination (discussed in previous section) these measures are not effective. An appropriate technology solution to arsenic is available in the Sono arsenic filterW. 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! Iron and manganese oxides can offer a cheap method of removing low levels of arsenic from water. The oxides are able to adsorb arsenic ions and remove them from solution. Rusty iron nails (ungalvanized) can also be used as adsorption media. [verification needed]
Protection of waterEdit
Water storage containers:
- Special buckets are now used in refugee camps which better protect the water from contamination.[verification needed]
- Education - e.g. not rubbing the insides of buckets with hands when cleaning them; not rinsing with water which has been used to rinse other buckets.
- Mosquito netting over any opening, especially for larger containers where water stands for a week or more. This is to prevent mosquito-borne diseases, as well as the discomfort of mosquito bites. There must be no holes in the netting. Also important for openings of septic tanks.
- PVC is sometimes regarded as a toxic plastic; however the problems for the end user result from the plasticizers, and thus PVC water pipe should be very safe. In fact PVC is considered to be the best material for not releasing impurities into the water (based on Sydney Water documents examined by Chriswaterguy in 1996). 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.
- See Wikipedia:Survival skills and Filtering & Purifying Water (from TheRangerDigest.com)
- 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.)
- Les Roberts describes the research which led to the use of such buckets - lecture 1 (or 2?), 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). (Links are needed here which show and describe the bucket and give more details.)
- The redlinks below are planned pages - feel free to make a start, especially if you have knowledge in these areas.
- Clearinghouse for low-cost household water treatment technologies
- rainwater catchment discussion at permies.com
- Simple prototype for water solar distillation
- LifeSaver bottles and jerry cans (a commercial solution starting at around £99 retail):
- Ted Talk: Michael Pritchard invents a water filter.
- wikipedia:LifeSaver bottle
- Life Saver systems] sell personal-scale (bottle/jerry can) water filtering systems.