Water filtration techniques

As part of my ongoing attempt to detail various skills that can be used in SHTF situations and which I am competent to speak about I present the next instalment. This is a general overview of filtration with respect to water and it assumes your trying to produce safe water in a SHTF situation. I would suggest that everyone had a good quality water filter and use this info for emergencies rather than as your preferred method. A pre-built system is always better than a scavenged one.

The removal of particles and pathogens from water can be done using three very broad methods. The first is chemical means, the second is physical means and the third is membrane.

Chemical Means
This involves adding something to the water to kill the pathogens or to cause the solids to precipitate out of the water. It also covers the technique of adsorption, in which a material is added to pull something out of the water.

The most common method of chemically treating water is to add chlorine to the water. I will not go into details on this method because so many other good threads have covered it in depth.

The most common type of Adsorption filters, are called Activated Carbon (AC) filters. The Brita ™ brand of pitchers use an AC filter in them. AC can be used to remove low molecular weight organics, reduce halogens such as chlorine and improve taste. It will not remove dissolved salts. AC filters have very low flow rates to give the water sufficient contact time to give up the contaminants to the AC. While AC removes chlorine and fluoride from water it can not be used as the method of removing bacteria. Some municipal systems use a holding tank where water is mixed with chlorine to kill the bacteria and then the water is sent through an AC filter to remove the chlorine taste. The other shortfall of AC filters is that they can quickly become a breading ground for bacteria, because of this they have a short life span once placed in service.


Physical Means
Physical means involve some sort of barrier that has very small holes through which the water can flow yet which are small enough to block the pathogen from travelling through.
As a general rule water filters need to block items as small as 0.1 microns to stop items like bacteria, though a filter rated for 0.003 is needed for viruses. This method will not take dissolved solids out of your water but is a good way of making water biologically safe (ie biologics are removed). Many of the common survival and travel filter use a barrier. The filter industry has several different was of rating filters. The most common is to give the micron rating of the filter such as 0.1 microns, this info alone is pretty much worthless to you. You would also need to find the efficiency rating to know how safe the filter is to use. A filter rated at 80% is considered industrial grade, but a 80% efficient 0.1 micron filter would still allow 20% of the bacteria 0.1 microns and larger to get through. Filters for food are usually rated at 90-95% and true high grade filters are above 99%. Some manufacturers for drinking water filters rate them at 99.99% (basicly 100% but they list it lower in case of law suites). These filters typically require pressure to force the water through the filter. These filters can be made of numerous materials depending on service, so materials are not suitable for drinking water and are intended for other services.

These types of filters are very commonly used in drink factories, produce washing facilities (where they clean lettuce etc), car washes (newer ones where they recycle the water), hospitals and industrial sites. Even fast food restaurants use these to filter the water used in the pop machines. The materials you should be looking for are ceramic and polypropylene. Some industrial ones are made of cotton or fibreglass. Some fibreglass filters are food safe, the common orange/rusty colored ones are not safe to use if found. Cotton filters tend to be rated at 50+ micron in size and are way to coarse of a filter to use in producing safe water. Usually these filters have a sort of plastic or steel enclosure (called a housing) that directs the water through the filter such that the water doesn’t go around (in industry this is referred to as bypass) the filter.


Membranes
Many people know of Reverse Osmosis filtration (RO) from buying bottled water in the store. RO uses special cross flow membranes to remove solids and dissolved solids from water. RO filters are nearly useless without the full system they fit into, so acquiring membranes without the system will not be helpful. RO systems also require power and pressure to push the water through the membrane and to keep the membrane clean. These systems are some of the best for water quality in that they can remove 99.99% of viruses and bacteria in some brands and styles. Usually the small home RO units are no where near this efficient but most hospitals have units like these to provide ultra pure water for immune compromised patients. Also electronic manufacturers use water this pure in the fabrication of circuit boards. These units provide the highest quality of water.

Contaminants in water - Dissolved metals

Iron
Effects the hardness of the water and can give water a metallic taste. If oxygen is bubbled through the water the iron will convert from a soluble to insoluble state. This allows it to be removed with a physical filter. Some bacteria use the iron as a food source and grow into a rust colored slimey sludge.

Manganese
Similar issues as iron but looks black when it precipitates out.

Sulfates
Sulphur & Oxygen compounds. In high concentrations this causes a bitter taste and acts as a laxative in humans.

Chlorides
High levels give water a slaty taste

Nitrates
Usually this is a contamination from industrial waste or fertillizer. They can fuel the growth of organics and in high levels are toxic. At mid levels they are toxic to infanst and young animals.

Aluminium
Very rare in natural water sources. Can be found in industrial waste contaminated water. Also care should be taken if drink water from a municipal treating plant that is not functioning properly. Some plants add Al2(SO4)3 as part of the process (it is removed in later stages. People with kidney problems are very badly effected by this contaminant.

Phosphates
Usually this is a contamination from detergents or fertillizers. Can fuel bacterial and fungal growth in the water.

Contaminants in water - Dissolved Gases


Carbon Dioxide
Forms carbonic acid and lowers the Ph of water

Hydrogen sulfide (H2S)
In high levels will come out if weather conditions change, H2S can be deadly as it is a neuro blocker and prevents automatic brain functions (such as breathing) from working. Can be found by the rotten egg smell.

Radon
usually found in water from granite formations. Can cause cancer in humans.

Good work exile! I have been working on a thread about water filtration
and purification in a wilderness environment. This would be more applicable to urban survival and you cover it pretty thoroughly. Thanks.

Very good posts. However dont forget collection of steam or distillation to get pure water in areas with heavy contamination.

Thanks everyone, yes most of this technology is better for urban enviroments. Though I was trying to cover the basics of industrial systems and how to salvage them for survival use.

I know a lot of small town fast food chains have really expensive systems to make the pop taste identical all across the country.

Steam distillation is an excellent method for killing most pathogens. The saran wrap to collect moisture from the ground is an excellent way too, though I'd be careful on a piece of land that has been spray with any sort of weed control product recently.

Contaminants in water - Heavy Metals

Lead, Arsenic, cadmium, Chromum all are toxic at relatively low levels. Children and the elderly are more effected. Also some medications are blocked if you have too much heavy metals in your system. This is why hospitals give RO water to certain patients.

The legal safe limit for lead is 15 parts per billion (PPB).

Here are the recommended maximum levels of contaminants allowed in water - these are recommended for safety reasons. But in the US none of these are enforceable as law since the EPA has them as guidlines.

Aluminium 0.05 mg/L
Chloride 250mg/L
Copper 1 mg/L
Fluoride 2 mg/L
Iron 0.3 mg/L
Manganese 0.05 mg/L
Silver 0.09 mg/L
Sulfate 250 mg/L
Zinc 5 mg/L

Total dissolved solids 500 mg/L
PH: 6.5 to 8.5

These are the contaminants that have legal maximums allowed in Drinking water.

Unless stated otherwise I have all of these listed as mg/L for units.

Arsenic 0.05
Asbestos 7 MFL
Barium 5
Cadmium 0.005
Chromium 0.1
Cyanide 0.2
Lead 0.05
Mercury 0.002
Nickel 0.1
Nitrate 10
Nitrite 1
Selenium 0.05
2,4-D 0.07
Lindane 0.0002
Benzene 0.005
Toluene 2


Lead and Mercury are per the pre-1990 EPA guidlines. Al others from the newest eddition of the guidlines. Lead and Mercury are not listed in the post 1990 EPA guides they are in other documents now.