The article is still far from comprehensive, but I’ll update it\u00a0from time to time with new information as I get it (or remember it!)<\/p>\n
A quick note on water supplies.<\/h2>\n
Regardless of which of these filters you use, they\u00a0will all work better with water that has been pre-filtered to remove gross sediment and turbidity<\/a>. \u00a0This can be done with something as unsophisticated as a t-shirt.<\/p>\n Also, be warned, none of these filters alone will remove heavy metals, pesticides, salt or other chemical contamination. \u00a0Additional activated carbon filters will help\u00a0remove some chemical contamination, but their effectiveness\u00a0depends on the dwell time (how long the water is in contact with the carbon) and the contact area – and commonly these are nowhere near enough to make a significant difference. \u00a0Thus, if your water supply is heavily contaminated with dangerous chemicals, you’ll need another way to get clean water. \u00a0For most people, the easiest and best way is to collect clean water for filtering\u00a0is from the sky using something else most people have, a roof. \u00a0Even if this becomes contaminated with bacteria, the filters will deal with that for you.<\/p>\n This is a class of filters that includes those\u00a0made by companies such as Sawyer and LifeStraw. \u00a0These filters, much like ceramic filters, work on\u00a0a simple idea: contaminants such as bacteria and viruses are larger than a molecule of water, therefore to remove the contaminants, one needs a filter medium that has channels that are\u00a0reliably larger than water but smaller than these contaminants. \u00a0There is an essential trade off in these filters: the smaller the channels, the slower the filtration, but the more types of contaminant it will remove.<\/p>\n These systems are mostly ‘gravity filters’ as\u00a0they rely on the force of gravity to force the water through the filter. \u00a0This means that their speed does vary as a function of the\u00a0relative hight of the water source (or pressure when driven by a tap).<\/p>\n A variety of companies use this technology, but Sawyer and LifeStraw stand out because their filters are rated to filter\u00a0a huge amount of water – and are cleaned rather than replaced. \u00a0To confuse matters however, each company makes a large number of different filters or filter sets. \u00a0I’m going to cover the main ones\u00a0below:<\/p>\n Following Ecuador’s\u00a0devastating earthquake in April 2016, a variety of organisations\u00a0brought down Sawyer filters to help. \u00a0These were invariably the\u00a0PointONE bucket filter system<\/a>. \u00a0The link I’ve provided is to a full set with tap adapter, but Sawyer generously provided a stripped down bucket system at a charity price of only $10 per filter, way below the normal cost of $50 for the full set.<\/p>\n Now these filters DO NOT filter viruses<\/strong>, so if there is any concern of viral infections, one should use the more expensive\u00a0Point ZeroTWO <\/a>systems. \u00a0In Ecuador, the risk of viral infection in the water source was considered minimal. \u00a0Other than being more expensive, these 0.02 filters are also much slower at filtering; while the 0.1 system can theoretically filter around 2000 litres per day, the 0.02 system can ‘only’ filter around 700l. \u00a0However, in both cases these number are theoretical, and rely on a constant source of non-turbid water with sufficient pressure.<\/p>\n CLEANING<\/strong>: \u00a0Depending on the level of contamination (sediment, bacteria, algae etc) in the water, the filter will need regular cleaning. \u00a0To test and demonstrate the filter to people on the coast, I spent two weeks drinking water\u00a0filtered from a very green source of water in an abandoned swimming pool (I sadly neglected to take photos, but I did survive). \u00a0In this fairly extreme case, the filter became\u00a0very slow after around 10 litres. \u00a0Cleaning of the filter is done by backwashing with clean\u00a0water using a syringe or a plastic drinking bottle with an adapter.<\/p>\n This process is very simple, but it is perhaps the one major\u00a0weak point of the filter. \u00a0When giving these filters out to poorly educated people, who may speak a different language from the donor, there\u00a0are a variety of possibilities for problems: the person may not understand the initial instructions, they may not understand what constitutes uncontaminated water or even if they do understand at first, they may forget in time. \u00a0And of course, one needs to have a source of uncontaminated water and have all the relevant attachments in order to carry out the backwashing.<\/p>\n Pressure issues<\/strong>: When driven by a tap (or a high cistern), the pressure can easily\u00a0be higher\u00a0than that for which the filter is rated. \u00a0According to what I’ve read from Sawyer, the filter is designed to leak in such cases to prevent actual damage to the filter. \u00a0However, if unnoticed (this can easily happen) the leaking source water can contaminate the output as it drips down.<\/p>\n CONTROVERSY<\/strong>: \u00a0Sawyer claim that their filters are good for ‘up to 1,000,000 gallons’ (4 million litres). \u00a0However, this has been disputed by researchers from Tufts university (article here<\/a>\u00a0and presentation here), who claim that the filters may be seriously degraded within 24 months of use. \u00a0The quality of the science behind the claim, has however been disputed by Sawyer (here<\/a> and here<\/a>) and by other academics (see here<\/a>). \u00a0While another\u00a0study appears to support the real world benefits of using the Sawyer filter in Bolivia<\/a>, it is worth noting that there do not seem to have been any proper long term field studies of the filters.<\/p>\n In the end, in Ecuador many groups\u00a0chose to go with the Sawyer filters because they are extremely portable (one can just buy the filter and buy buckets in the destination area), but mostly because Sawyer has made them available so cheaply for charitable use. \u00a0One could buy 8 PointONE filters for the price of a LifeStraw Family filter. \u00a0I also now use one in my house in Ecuador for drinking water as it’s quicker and easier than the ceramic filter I had before. \u00a0The max flow rate of the Sawyer (which does not filter viruses) is 10 times that of the LifeStraw filters. \u00a0See here<\/a> for a spreadsheet comparing the filters (a work in progress).<\/p>\n In Ecuador where I’m based, ceramic filters are quite popular for household drinking water.<\/p>\n I used filters like this for a couple of years and they work fine. \u00a0The biggest disadvantage is that they are slow and require work to fill and maintain. \u00a0They can achieve around 1-2l\/h (depending on age and amount of water in the top container), which is ok if you are organised, but you can’t expect to have water right away of you forget to fill it. \u00a0The containers will also develop algae if they are not regularly used and kept away from light. \u00a0Furthermore, as with all filters that store water,\u00a0the clean water can become contaminated, so regular cleaning is recommended. \u00a0The cost is around \u00a330 for a complete system and $6 for the filters ($12 for both), which need to replaced every 6 months or so.<\/p>\n The ceramic pots themselves are designed to sit easily into a standard plastic bucket which can be fitted with a tap (see image). Locally manufactured pots have the advantage that they support the local community and likely have a reduced carbon footprint compared to imported versions. \u00a0They may be particular useful for use in very poor and isolated communities where imported systems are unlikely to be regularly available. \u00a0A possible downside is that the pots might not always be correctly manufactured – the rule of thumb is that if they have a flow rate of more than two to\u00a0three litres per hour they are not working. \u00a0A scientific analysis of both this filter system and biosand systems can be downloaded\u00a0here<\/a>. \u00a0 The ceramic pots may be bought for between $20 and $30. \u00a0Only the recent development of filters such as the Sawyer membrane filter have made this look like less of a good deal.<\/p>\n Ceramic filters can also be bought to be plumbed in to service a whole house and can have pretty impressive flow rates with sufficient pressure. \u00a0This<\/a> 0.9 micron system from Doulton (for example) has a flow rate of 1000l\/hour at 40 PSI (1.4 Bar\/14m head). \u00a0Note however the relatively large size of the filter. \u00a0This WILL let through some bacteria (and definitely viruses); it seems Doulton are is relying on only the bigger bacteria being pathogenic and say<\/a> the filter removes 99.99%+ of these..<\/p>\n Another very interesting option. \u00a0BioSand filters are based on the slow sand filters that clean municipal water throughout the world, including that of major cities such as London. \u00a0They use both physical and biological methods to clean the water. \u00a0The physical is the sand, gravel and sometimes activated carbon. \u00a0This upper layer of find sand\u00a0supports a biological top layer, known as a biofilm,\u00a0 hypogeal<\/a> layer or for those who like german words,\u00a0Schmutzdecke<\/a>. \u00a0\u00a0<\/i>The biofilm\u00a0layer provides the bacterial\u00a0reduction which can be up to 99% in a well functioning filter. \u00a0A new filter has a much lower\u00a0efficiency, which gradually builds up over time. \u00a0Importantly these filters CAN NOT be used with municipal\u00a0water supplies, as the chlorine\u00a0will kill the biofilm. \u00a0The cost of a system is basically the cost of the container (generally a 50 gallon plastic water butt or a concrete alternative), the sand, some piping and a tap. \u00a0 In total this might be $50 or so.<\/p>\n An unpublished analysis<\/a>\u00a0by Duke, Nordin & Mazumder suggests that biosand filters may be very useful as a first line treatment for water, perhaps for washing, cooking and showering (as they can quickly remove the majority of contamination and turbidity at circa 19l\/h), but due to their variable efficiency at removing bacteria, should be complimented with ceramic filters for drinking water. \u00a0For further information see wikipedia<\/a> and this<\/a> construction manual from CAWST<\/a> (Centre for Affordable Water and Sanitation Technology).<\/p>\n The bacteria and viruses in water can also be killed via UV light. \u00a0This is the basis of many pond treatment systems, but is also used for household water treatment and the portable Steripen. I’ve not used on, but it’s a pretty good solution assuming that you have a source of \u00a0non-turbid water. \u00a0Perhaps the best thing is that you will be certain as to whether\u00a0it’s working or not (if the light comes on, it works and your water will be treated). \u00a0Some\u00a0potential downsides are: 1. It is an active system, which means it can run out of batteries and may go wrong; 2. It can only treat a small amount of water at a time, making it best for individual use; 3. It needs clear water and will not filter or treat turbid water properly. \u00a04. \u00a0There a plenty of reports of the Steripen being unreliable (among plenty of other singing it’s praises). \u00a0All in all, it’s an interesting alternative to filters for personal water treatment (if you a travelling where there is not a clean water supply, always carry a backup such as bleach drops). \u00a0The steripen retails for about \u00a370\/$70.<\/p>\n At a household level, it is possible to buy inline UV treatment lamps. \u00a0I’ve never used one personally, although I’ve seen one in action at the Brighton<\/a> demonstration earthship (a UV filter is not very exciting to watch though). \u00a0These retail at around \u00a3500\/$500 (see here<\/a> for an example capable of 60l\/h) . and require a source of electricity and yearly replacement of the lamps. While probably a good option for many, they may not make the best solution for disaster preparation (they would be vulnerable in an earthquake and not function without power). \u00a0They will also need pre-filtration in many cases.<\/p>\n I’m posting this now to make it available for feedback. \u00a0It’s not finished yet, but some people have been waiting for it, so I thought I’d get it posted.<\/p>\n","protected":false},"excerpt":{"rendered":"Membrane\u00a0Filters<\/h2>\n
Sawyer<\/h3>\n
![\"bucket2\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/04\/bucket2.jpg?resize=265%2C300\")
<\/a>Sawyer’s<\/a> filters come in two\u00a0filtration levels. \u00a0The Point ZeroTWO (0.02\u00a0micron) filter will essentially filter all protozoa, bacteria and viruses, while the\u00a0\u00a0PointONE (0.1 micron will filter bacteria and\u00a0protozoa, but NOT viruses). \u00a0Each type of filter is sold\u00a0in a variety of different setups: including systems that filter from one bag or bucket to another and systems that plug directly into your tap (faucet for you North Americans).<\/p>\nLifeStraw<\/h3>\n
![\"LifestrawFamily-01\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/04\/LifestrawFamily-01.jpg?resize=144%2C300\")
<\/a>LifeStraw’s eponymous filter is a straw for drinking directly out of rivers\/ponds, and seems\u00a0impractical for most real world uses, except travel emergencies. \u00a0However, LifeStraw also make a variety of filters designed for families and communities. \u00a0For example, the LifeStraw Family<\/a>\u00a0is rated for 18,000 litres and filters at 0.02 microns (removing virtually all bacteria and viruses from the water). I’ve seen the family version in action, and it’s looks good. \u00a0In particular, it has a clever integrated backflush mechanism that should eliminate the possibility of contamination while cleaning. \u00a0The retail price is around $80 on Amazon<\/a>.<\/p>\n![\"\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/P4291432.jpg?resize=225%2C300\")
<\/a>The\u00a0communit<\/a>y version\u00a0is much larger and more expensive. \u00a0It is rated for around 70,000 litres. \u00a0I’ve never seen this version\u00a0in action; it looks like a good product, but it’s relatively expensive and bulky. \u00a0On Amazon<\/a> right now it costs over $500. \u00a0Like the family version, it comes with an integrated backflush, and it also comes with a pre-filter for sediment.<\/p>\nCeramic Filters<\/h2>\n
![\"copyright](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/19027449.jpg?resize=175%2C300\")
<\/a>The first modern ceramic filter was ‘invented’ by\u00a0Henry Doulton<\/a>, who\u00a0\u00a0devised\u00a0the modern ceramic candle filter in 1827. \u00a0However, ceramics were\u00a0reportedly\u00a0used to filter water long before that (I’m still searching for a good article on this). \u00a0Ceramic filters generally come in two forms, the replaceable ‘candle’ (which includes the traditional Doulton version on the right and the modern plastic you can see below), and the ceramic pot.<\/p>\nShop Bought.<\/h2>\n
![\"\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/81AbH9-mnkL._SL1500_.jpg?resize=225%2C300\")
<\/a>This is the standard model and can sometimes be bought in shops, and can always be bought online (see here<\/a>). \u00a0It consists of two compartments and two filters. \u00a0The filter you can see in the upper (dirty water) compartment is the ceramic filter. \u00a0This will theoretically remove all bacteria and viruses. \u00a0 The filter in the lower compartment contains a variety of components,\u00a0including activated carbon to remove contaminants (the black stuff at the top) and others which I guess are supposed to introduce minerals into the water.<\/p>\nLocally Manufactured pots<\/h2>\n
![\"\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/Screen-Shot-2017-07-15-at-11.21.08-copy.jpg?resize=300%2C223\")
<\/a>This is a very interesting option for low income countries – albeit perhaps less so since the introduction of other low cost alternatives. \u00a0This system in its ‘modern’ incarnation was developed in\u00a0Guatemala in 1981 by Dr. Fernando Mazariego. \u00a0In 1986, Ron Rivera of \u00a0‘Potters for Peace<\/a>‘ collaborated with Mazariego to develop the technique and since then has been helping to export the idea around the world (for instance this\u00a0in\u00a0Cambodia<\/a>, and I have contact details for manufacturers in Ecuador if anyone wants them). \u00a0These filters can be made by traditional potters using a technique which involves adding a fine inflammable material (such as finely ground rice or coconut husks) to the clay. \u00a0When the pots are fired, this material incinerates leaving fine channels in the pot, through which the water will filter, but through which the bacteria and viruses struggle to pass. \u00a0This process removes around 95% of the bacteria and viruses, which can be improved closer to 100% via the addition of colloidal silver.<\/p>\n![\"\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/filter.jpg?resize=131%2C198\")
<\/a><\/p>\nWhole house systems<\/h3>\n
BioSand Filters<\/h2>\n
![\"\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/Ohorizons_Concrete_BioSand_Filter.png?resize=178%2C300\")
<\/a>UV water treatment.<\/h2>\n
\n![\"\"](\"https:\/\/i0.wp.com\/ferguskane.com\/blogs\/wp-content\/uploads\/2017\/07\/Opti-in-bttle_moss1448-500x500.jpg?resize=300%2C300\")
<\/a>The Steripen is a very popular water treatment system for backpackers. \u00a0Basically you put the steripen in a bottle of water, turn it on and stir the water. \u00a0The UV light does all the rest.<\/p>\nThat’s it for the moment. \u00a0More later.<\/h3>\n