Water Filtration 2. Systems

Here I attempt to summarise some of the options for providing safe water, both for disaster preparation and  for general travel in areas where there is limited access to potable water (or where you’d prefer not to have to buy bottled water).

It’s a delayed follow-up to my first post on water filters, which focussed on the rationale of ensuring that people (especially in disaster prone areas such as Ecuador) have water autonomy.  Both posts were inspired by my work following the Ecuadorian earthquake of April 2016.

The article is still far from comprehensive, but I’ll update it from time to time with new information as I get it (or remember it!)

A quick note on water supplies.

Regardless of which of these filters you use, they will all work better with water that has been pre-filtered to remove gross sediment and turbidity.  This can be done with something as unsophisticated as a t-shirt.

Also, be warned, none of these filters alone will remove heavy metals, pesticides, salt or other chemical contamination.  Additional activated carbon filters will help remove some chemical contamination, but their effectiveness depends 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.  Thus, if your water supply is heavily contaminated with dangerous chemicals, you’ll need another way to get clean water.  For most people, the easiest and best way is to collect clean water for filtering is from the sky using something else most people have, a roof.  Even if this becomes contaminated with bacteria, the filters will deal with that for you.

Membrane Filters

This is a class of filters that includes those made by companies such as Sawyer and LifeStraw.  These filters, much like ceramic filters, work on a 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 reliably larger than water but smaller than these contaminants.  There 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.

These systems are mostly ‘gravity filters’ as they rely on the force of gravity to force the water through the filter.  This means that their speed does vary as a function of the relative hight of the water source (or pressure when driven by a tap).

A variety of companies use this technology, but Sawyer and LifeStraw stand out because their filters are rated to filter a huge amount of water – and are cleaned rather than replaced.  To confuse matters however, each company makes a large number of different filters or filter sets.  I’m going to cover the main ones below:


bucket2Sawyer’s filters come in two filtration levels.  The Point ZeroTWO (0.02 micron) filter will essentially filter all protozoa, bacteria and viruses, while the  PointONE (0.1 micron will filter bacteria and protozoa, but NOT viruses).  Each type of filter is sold in 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).

Following Ecuador’s devastating earthquake in April 2016, a variety of organisations brought down Sawyer filters to help.  These were invariably the PointONE bucket filter system.  The 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.

Now these filters DO NOT filter viruses, so if there is any concern of viral infections, one should use the more expensive Point ZeroTWO systems.  In Ecuador, the risk of viral infection in the water source was considered minimal.  Other 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.  However, in both cases these number are theoretical, and rely on a constant source of non-turbid water with sufficient pressure.

CLEANING:  Depending on the level of contamination (sediment, bacteria, algae etc) in the water, the filter will need regular cleaning.  To test and demonstrate the filter to people on the coast, I spent two weeks drinking water filtered from a very green source of water in an abandoned swimming pool (I sadly neglected to take photos, but I did survive).  In this fairly extreme case, the filter became very slow after around 10 litres.  Cleaning of the filter is done by backwashing with clean water using a syringe or a plastic drinking bottle with an adapter.

This process is very simple, but it is perhaps the one major weak point of the filter.  When giving these filters out to poorly educated people, who may speak a different language from the donor, there are 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.  And of course, one needs to have a source of uncontaminated water and have all the relevant attachments in order to carry out the backwashing.

Pressure issues: When driven by a tap (or a high cistern), the pressure can easily be higher than that for which the filter is rated.  According to what I’ve read from Sawyer, the filter is designed to leak in such cases to prevent actual damage to the filter.  However, if unnoticed (this can easily happen) the leaking source water can contaminate the output as it drips down.

CONTROVERSY:  Sawyer claim that their filters are good for ‘up to 1,000,000 gallons’ (4 million litres).  However, this has been disputed by researchers from Tufts university (article here and presentation here), who claim that the filters may be seriously degraded within 24 months of use.  The quality of the science behind the claim, has however been disputed by Sawyer (here and here) and by other academics (see here).  While another study appears to support the real world benefits of using the Sawyer filter in Bolivia, it is worth noting that there do not seem to have been any proper long term field studies of the filters.


LifestrawFamily-01LifeStraw’s eponymous filter is a straw for drinking directly out of rivers/ponds, and seems impractical for most real world uses, except travel emergencies.  However, LifeStraw also make a variety of filters designed for families and communities.  For example, the LifeStraw Family is 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.  In particular, it has a clever integrated backflush mechanism that should eliminate the possibility of contamination while cleaning.  The retail price is around $80 on Amazon.

The community version is much larger and more expensive.  It is rated for around 70,000 litres.  I’ve never seen this version in action; it looks like a good product, but it’s relatively expensive and bulky.  On Amazon right now it costs over $500.  Like the family version, it comes with an integrated backflush, and it also comes with a pre-filter for sediment.

In the end, in Ecuador many groups chose 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.  One could buy 8 PointONE filters for the price of a LifeStraw Family filter.  I 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.  The max flow rate of the Sawyer (which does not filter viruses) is 10 times that of the LifeStraw filters.  See here for a spreadsheet comparing the filters (a work in progress).

Ceramic Filters

copyright unknownThe first modern ceramic filter was ‘invented’ by Henry Doulton, who  devised the modern ceramic candle filter in 1827.  However, ceramics were reportedly used to filter water long before that (I’m still searching for a good article on this).  Ceramic 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.

Shop Bought.

In Ecuador where I’m based, ceramic filters are quite popular for household drinking water.

This is the standard model and can sometimes be bought in shops, and can always be bought online (see here).  It consists of two compartments and two filters.  The filter you can see in the upper (dirty water) compartment is the ceramic filter.  This will theoretically remove all bacteria and viruses.   The filter in the lower compartment contains a variety of components, including activated carbon to remove contaminants (the black stuff at the top) and others which I guess are supposed to introduce minerals into the water.

I used filters like this for a couple of years and they work fine.  The biggest disadvantage is that they are slow and require work to fill and maintain.  They 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.  The containers will also develop algae if they are not regularly used and kept away from light.  Furthermore, as with all filters that store water, the clean water can become contaminated, so regular cleaning is recommended.  The cost is around £30 for a complete system and $6 for the filters ($12 for both), which need to replaced every 6 months or so.

Locally Manufactured pots

This is a very interesting option for low income countries – albeit perhaps less so since the introduction of other low cost alternatives.  This system in its ‘modern’ incarnation was developed in Guatemala in 1981 by Dr. Fernando Mazariego.  In 1986, Ron Rivera of  ‘Potters for Peace‘ collaborated with Mazariego to develop the technique and since then has been helping to export the idea around the world (for instance this in Cambodia, and I have contact details for manufacturers in Ecuador if anyone wants them).  These 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.  When 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.  This process removes around 95% of the bacteria and viruses, which can be improved closer to 100% via the addition of colloidal silver.

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.  They may be particular useful for use in very poor and isolated communities where imported systems are unlikely to be regularly available.  A 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 three litres per hour they are not working.  A scientific analysis of both this filter system and biosand systems can be downloaded here.   The ceramic pots may be bought for between $20 and $30.  Only the recent development of filters such as the Sawyer membrane filter have made this look like less of a good deal.

Whole house systems

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.  This 0.9 micron system from Doulton (for example) has a flow rate of 1000l/hour at 40 PSI (1.4 Bar/14m head).  Note however the relatively large size of the filter.  This WILL let through some bacteria (and definitely viruses); it seems Doulton are is relying on only the bigger bacteria being pathogenic and say the filter removes 99.99%+ of these..

BioSand Filters

By OHorizons – ohorizons.org, CC BY 3.0

Another very interesting option.  BioSand filters are based on the slow sand filters that clean municipal water throughout the world, including that of major cities such as London.  They use both physical and biological methods to clean the water.  The physical is the sand, gravel and sometimes activated carbon.  This upper layer of find sand supports a biological top layer, known as a biofilm,  hypogeal layer or for those who like german words, Schmutzdecke.   The biofilm layer provides the bacterial reduction which can be up to 99% in a well functioning filter.  A new filter has a much lower efficiency, which gradually builds up over time.  Importantly these filters CAN NOT be used with municipal water supplies, as the chlorine will kill the biofilm.  The 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.   In total this might be $50 or so.

An unpublished analysis by 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.  For further information see wikipedia and this construction manual from CAWST (Centre for Affordable Water and Sanitation Technology).

UV water treatment.

The bacteria and viruses in water can also be killed via UV light.  This is the basis of many pond treatment systems, but is also used for household water treatment and the portable Steripen.
The Steripen is a very popular water treatment system for backpackers.  Basically you put the steripen in a bottle of water, turn it on and stir the water.  The UV light does all the rest.

I’ve not used on, but it’s a pretty good solution assuming that you have a source of  non-turbid water.  Perhaps the best thing is that you will be certain as to whether it’s working or not (if the light comes on, it works and your water will be treated).  Some potential 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.  4.  There a plenty of reports of the Steripen being unreliable (among plenty of other singing it’s praises).  All 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).  The steripen retails for about £70/$70.

At a household level, it is possible to buy inline UV treatment lamps.  I’ve never used one personally, although I’ve seen one in action at the Brighton demonstration earthship (a UV filter is not very exciting to watch though).  These retail at around £500/$500 (see here 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).  They will also need pre-filtration in many cases.

That’s it for the moment.  More later.

I’m posting this now to make it available for feedback.  It’s not finished yet, but some people have been waiting for it, so I thought I’d get it posted.

High Altitude Gardening – SIPping

(Utilice el menú desplegable de la izquierda para seleccionar Español)
The finished product

Just about everything in Quito comes with its own special challenges.  The altitude and climate provide plenty of scope for things to go pear-shaped,  and mean that, from boiling an egg though to baking and gardening, nothing can be taken for granted.

In Quito, there can be downpours for days, followed by weeks with no rain at all.  The sun is  powerful and evaporation is faster due to the lower pressure.  This all makes gardening a challenge, especially for pots and planters, which can dry in a matter of hours.

But all is not lost.  Step up SIPs!  SIPs = Sub Irrigated Planters.

What is a SIP?

Wikipedia’s page is pretty poor, but there are plenty of resources to be found around the web and a community of avid enthusiasts.  And this enthusiasm is not surprising, because SIPs are amazing!  I’ve enjoyed the process and the results so much I’ve become an evangelist (hence this entry).

A SIP is any method of watering plants where the water is introduced from the bottom, allowing the water to soak upwards to the plant through capillary action (Wikipedia).

So, why SIP?  

  • SIP because you don’t want to water everyday.
  • SIP because you don’t want to waste water.
  • SIP because you don’t want to kill your plants through under or over watering.
  • SIP because you’re lazy.
  • SIP because you  just want to.

The basic principles of SIPs:

Essentially a SIP aims to emulate to some extent the way plants work naturally.  Plants generally suck up water from below, taking what they need.  Traditional pots and planters turn this upside down, with the water introduced from the top.  This is rather foolish, maximising evaporation and risking both over and under-watering.  One consequence of this is that we’re sensibly advised to water in the evening to reduce evaporation.  With a SIP, you can water effectively anytime.

There are lots of different designs for SIPS, but the best take into account the following priciples:

  • Water is fed in through a tube which feeds a reservoir in the base of the planter.
  • This tube also allows air to enter into the reservoir, this enters the soil via small holes.
  • An overflow is provided just below the top of the reservoir, this prevents overwatering and maintains an airspace.
  • A wicking material (cloth, newspaper or just soil) allows the water to reach the plant via capillary action.
  • Where appropriate, a mulch or newspaper should cover the soil to further prevent evaporation.

How to buy/make a SIP?

Although you can, there is no need to buy a SIP.  I highly recommend making your own, using the above principles, and drawing on the wealth of designs on the web.  And if possible try to reuse and recycle to do so.

Let’s start simple and move on… Perhaps the most basic SIP is the single soda bottle SIP.  Here’s my schematic:

SIP Bottle

And here’s the real world version
(click on the image for a larger copy).  

This design does, in the name of simplicity, violate my first principal of a good SIP, in that it has no tube to feed the reservoir

Here the SIP is growing oregano.  Generally the occasional rain is enough to water it, the water passes through the soil and fills the reservoir; however sometimes I do need to add extra water – a tube would make this more efficient but would also complicate the simple, easy design.

I’ve also used this design for growing coriander from seed, this worked very well, reducing the chances of the soil drying out and the seedlings dying.

My assistant.

Ok, so what about more sophisticated designs?
SIPs are pretty much only limited by your imagination, and provide a lovely opportunity to get creative.  Following a few other attempts I I settled on this design for long planters.  Here I’ve used a variety of old bottles and some old tubing.  The three white bottles are all joined together and fill directly from the tube.  I drilled small holes (with a Dremel, but they could be punched or cut) in the tops and sides.  The top holes allow air to the soil, the side holes release water into the surrounding soil (added later!).  The transparent bottles are not connected to the white bottles but fill up as water exits the white bottles.


Overflow.  If you look closely, you’ll see that the vinegar bottle sticks though the side of the planter, thus acting as the overflow.  Excess water from the soil enters into the three transparent bottles, and when it reaches the level of the  exit hole (vinegar bottle top) it pours out of the planter, preventing overwatering.  The nice thing about this design is that if for any reason you want to really soak the planter (perhaps you’re going away for a while), all you have to do is put the lid back on the vinegar bottle (remembering to remove it when the soil has soaked).

Fill Pipe
Fill Pipe

Fill Pipe.  The fill pipe is topped by the top section of a plastic bottle. I generally join these to the pipe by cutting a hole in the lid, and then sealing the connection with a glue gun.

For the finished product, see the top of the article!

What else?

For me this is pretty much the beginning, there are plenty of ways of improving these systems, including developing a way to make a truly self watering SIP (again, there are plenty of ideas around on the web).  The bigger project is to make a large self watering planter using rain water.  I’ll update when I’ve made some progress!  In the meantime, try for yourself, and let me know how you get on.