Disinfection with Potassium Permanganate

Potassium Permanganate is a very versatile chemical. It can be used for disinfection, removing hardness, removing iron and manganese. It has another health related use, it can be mixed into a paste and used as a topical salve for athlete’s foot (or similar problems). As a result potassium permanganate is a great addition to any emergency preparedness supplies.

Potassium Permaganate has the chemical formula of KMnO4, and it comes as a deep purple dry powder. This chemical is a very powerful oxidizer and it should not be stored anywhere near acids or fuel sources or it could result in fires, explosions and/or toxic gases being formed. Explosives is another use of this chemical (one which I will not be explaining here). This chemical can be stored for over a year if it is kept clean and dry and in a sealed container.


Before touching the dry powder, make sure you wear a particle mask (ideally a N95 or better). This chemical will irritate the airways if inhaled directly. Also the powder once mixed with water becomes a powerful dye. It will stain clothes permanently, stain skin temporarily and cause corrosion on any metal or masonry it touches. Anything that becomes exposed to a potassium permanganate solution becomes brown, a similar shade of brown to a henna tattoo.

To make a topical treatment with KMnO4 mix the dry powder with water until it has the consistency of playdoh. Apply the mixture on the affected area and repeat as necessary. Remember that I am not a doctor and I am not giving medical advice. I am only outlining that this chemical CAN be used for medical purposes. Whether or not you SHOULD use KMnO4 for medical applications is not something I can tell you.


Potassium permanganate is very similar to sodium hypochlorite in the sense that they both disinfect water through oxidation. Disinfection of drinking water can be achieved by adding it to the water until the water turns pink. The pink in the water is the residual potassium permanganate. Meaning that there is nothing left to use up the chemical and any bacteria has been used. Think of the pink water as being similar to the point where you can smell bleach when using sodium hypochlorite for disinfection. Just like with the smell point of bleach has surpassed the disinfection point, you do not need to keep adding KMnO4 until you see pink. Disinfection has occurred well before you can see a lasting pink tint to the water. Using the color change is a simple and easy to remember method for disinfection of drinking water. And if the pink tint disappears at any time then you know you need to add more of the chemical to redisinfect the water.
If you want to avoid pink water and spend less money on chemicals you can buy a testing kit for manganese. Most kits can measure the residual levels of KMnO4 at levels well below the pink water threshold and well above the disinfection requirements.


For better results with disinfection it is best to filter the water through a greensand filter. Now this is not an indication of the color of the sand (it is actually black in color). Greensand is an activated filter media designed for removing iron and manganese through a process called ion exchange. The good news with a greensand KMnO4 combination is that the potassium permanganate will reactivate the filter media.

One thing to note is that potassium permanganate once added to water will make the water more corrosive. If the water is very pink it can also stain any container it is stored in. The pink water is perfectly safe to drink. I mean the water is not dangerous because of the pink coloring. It may however be dangerous for another reason or contaminant.

Another thing to note about KMnO4, is that if you add it to chlorinated water it will form a percipitate (solid). This is manganese dioxide, it is harmless except it will consume all the available chlorine in your water leaving you open to contamination from microorganisms.

With a few simple precautions KMnO4 is an excellent chemical to have on hand. It can be stored longer than sodium hypochlorite (bleach) and it can be added directly to the water unlike calcium hypochlorite. It also is very easy to see when enough of the chemical has been added. If there is a lasting pink tint that doesn’t disappear with time then the water has been disinfected.

When it comes to disinfecting your own drinking water, always be careful with the quality of chemical you use. They are not all created equal. The north american standard for chemicals used in drinking water is NSF/ANSI 60. Choose chemicals that meet this standard above ones that don’t. The will be significantly safer for your health and well being.

As with all my disinfection articles, I will remind you to always drink the safest water you can and combining treatment techniques is the best way to achieve safe drinking water

Can I use a storm-water pond as a back-up source of water?

Storm-water ponds are the closest alternative source of water for many people living in urban areas. In an emergency this source of water may be all that is available to you.  Eventually any water you have stored will be consumed and the water in a storm-water pond may be the difference between life and death.  With the proper treatment your local storm-water pond can be a great backup source of drinking water.

Industrial storm-water pond (source: info.evergreen.ca)

Storm-water presents a unique set of challenges during treatment. Because storm-water ponds collect surface water, the water is exposed to all the contaminants on the ground in the catchment area. This includes but is not limited to pesticides and fertilizers applied to lawns, motor oil and gasoline leaking from vehicles and litter like cigarette buts. It all ends up is the storm-water pond. Those chemicals are already in storm-water ponds on a normal day. During an emergency there may be additional contamination from sewage runoff from an overloaded or broken sewage system. The water in the pond will also contain all the microorganisms like ecoli, giardia and cryptosporidium normally in surface water. Any one of these will make you very sick if you get infected with them.
Finally, there will be high levels of nitrates in storm-water ponds. Too much nitrates consumed by young children can cause blue baby syndrome.

The first step in treating water from a storm-water pond is straining. Straining the water through a cloth or loose sand filter will remove large particles (ones you could pick up with your fingers). Remove as much of the suspended particles from the water as you can. Straining the water first will extend the life of your proper water filter.

If you have a clarifying agent like aluminum sulfate, this is the best time to add it to the water.  It will make contaminants too small to be filtered become attracted to each other and become significantly larger.  Larger particles are easier to remove from the water. Let the water sit still for at least 30 minutes without disturbing it.  All the newly formed large particles (called floc) will sink to the bottom.  When you take the water from this container, make sure you leave the majority of the settled material at the bottom of the container.

Urban Storm-water pond (source: greenbmp.blogspot.com)

The next step is to filter the water. Filter the water even if it looks clear, the human eye is five times too weak to detect dangerous levels of particles. Filter the water at least once through an activated carbon filter. Activated carbon is known to remove many different chemicals from water including pesticides, chlorine and fluoride. Activated carbon is not the same as charcoal. Charcoal is similar, it can remove toxins from water but it is nowhere near the efficiency of activated carbon.

The third step is oxidation. Oxidation will help with disinfection as most disinfectant chemicals are also oxidizers. Chemicals like sodium hypochlorite and potassium permanganate are both oxidizers and disinfectants. Oxidation will break down many of the remaining contaminants and inactivate many of the remaining bacteria. Keep adding the oxidizer/disinfectant till you can detect a residual after 20 minutes. The 20 minutes is the minimum you should wait for a gallon of water. Wait longer for larger volumes. This is because oxidation is a chemical reaction that isn’t instant. It needs time to complete the reaction.

The fourth step is to filter the water again. Filtering again is necessary because the disinfection/oxidation step will create some potentially carcinogenic byproducts. We filter before oxidation to minimize the amount of chlorine (or other chemical) and to limit the possibility of forming dangerous byproducts. We filter the second time to remove any byproducts that have been formed.

The final step is to boil the water.  This will help with disinfection, but the main goal of boiling at this point is to remove any volatile chemicals.  Any chemical with a boiling point lower than water will be removed after boiling.

A note about disinfection.  If all of these steps are followed there is no need for a step dedicated for disinfection.  Between the oxidation and the boiling of the water any microorganisms will be inactivated.  If you are storing the water for a long time then add some sodium hypochlorite for a residual disinfectant.  The residual disinfectant will prevent the water from becoming recontaminated before you drink it.

One additional possible step is to aerate the water.  Ponds are frequently stagnant.  Stagnant water is green with algae, it smells bad and tastes worse. After the water is made potable, transfer the water back and forth between two glasses. This adds oxygen to the water and will make the water taste better.

This may seem like a lot of work for something as small as a storm-water pond.  What I have described are the basic steps to turn the potentially toxic water in the pond into clean and safe drinking water.

Water Preparedness: Common Beginner Mistakes

Are you thinking about starting to store water? How about emergency water treatment? Getting started can be a very daunting task. Where should efforts be focused? What pitfalls should be avoided?  This article will explore a few of the mistakes I see people make when they start to take their personal water security seriously

Don’t be left without potable water. Avoid beginner mistakes. (source: always foodie.com)

The very first thing to learn is that there is no magic bullet. There is never a single product or technique which will always make water safe to drink. Combining, knowledge, multiple storage/treatment techniques and multiple products for storage/treatment is the best way to guarantee a safe source of drinking water for yourself and your family.  This logic or philosophy of combining as many protections as possible is used by municipal water systems all across North America.  It is referred to as a multi-barrier approach and it boils down to having many different protective measures to prevent contamination, in the event that one barrier fails, there are still many others in place.  To put it in layman’s terms, when it comes to water security, it isn’t a good idea to put all your eggs in one basket.

Marketing campaigns will make all sorts of claims about water products. Some will be irrelevant, like claims of BPA free plastic when the product is made from a type of plastic that never had BPA. Other claims will be over stated. The claim that is most often overstated is the number of times a water treatment product can be used. The quality of the water being treated is too variable for any company to give you an absolute number of times. This might not be done to deceive you. It could just be that the water they tested the product with was easier to treat then your water. Remember that no product will make the water perfect.  They will make the water safer when used correctly, if used incorrectly many water treatment products can make the water significantly more dangerous to drink.

Water needs to be stored in an appropriate container. This container needs to be able to physically hold the weight of the water and not leach any chemicals into the water. Assuming any garbage can sized container is appropriate will at best lead to soggy disappointment and at worst a severe case of gastrointestinal disease. For more information on water storage, read The Why? How? and How Much? of Water Storage?

Once your water is stored it needs to be kept safe. Water can become contaminated at any time. Anytime the container is open there is potential for contamination to occur. Read this article to find out what to do when your backup source of water becomes contaminated. The assumption that water only needs to be treated once is false. What was once safe to drink may be very dangerous when you need it if your aren’t protective of your supply. Water can turn stagnant when stored for long periods of time. Stagnation while not a health hazard is a taste hazard. Stagnant water tastes bad. Adding air to the water is how you relieve stagnation. Adding air is as simple as passing the water from one glass to another repeatedly or stirring the reservoir. The goal is to increase surface contact between the atmosphere and the water. It is important that aeration of the water will also remove the remaining chlorine (if any was present) in the water. If you are aerating the reservoir make sure you add some more disinfectant. Do this so you can keep your disinfectant residual high enough to keep the water contamination free.

Another mistake people make, is they store water but make no changes for reducing the water they use. Forgetting to change behavior during a crisis is probably the biggest mistake beginners make. Different situations require different behavior, this applies to your personal water use. You will be amazed at how much water is used if you aren’t careful. What could last a week might be used in a day and then you will understand the true value of water conservation. This mistake can also happen in more than just your water use.  For more information on water conservation read why water conservation is a prepper’s must do.

The single biggest mistake beginners is they assume that they can learn how to treat water later. Later becomes too late and then it can become fatal. It is very difficult to learn something complicated like water treatment when your life depends on it. Learning as much as you can before an emergency strikes is the single best thing you can do to stay safe.

This article covers just a few of the common mistakes I see people make when they start taking their water security more seriously.  There are many more mistakes that can be made and no one person has the perfect solution to them all. Water security is something that needs to be tailored to each person or family’s needs.  Have you found any common mistakes while preparing for water shortages? If so, leave a comment below, I would love to hear them.

Why?, How? And How Much? Of Storeing Water

Storing water is often the fist step in becoming more prepared. People need water everyday for a variety of reasons. Humans can go up to three days without water, however the effects of dehydration can be felt in as little as a few hours if you aren’t careful. In an emergency water use and water needs will change and they will never change in ways where you need less water.

On the surface storing water is just filling containers with water and walking away. If that is all you do then you will regret walking away relatively quickly. The only thing worse than ignoring your stored water is not having any stored water.

Why store water? It buys you time. Time to “wait it out” or time to find more water. This time will allow you to focus on and accomplish other tasks. Other demands for your time will abound in even a minor emergency. If keeping some water around means you can focus on security or damage control then it is definitely worth the effort.  I have written another article about why a back up supply of water is important.

Plastic Bottles are a Simple Way to Store Water (source: quiet-environmentalist.com)

How water can be stored depends on a few factors. Cost and storage space are the biggest factors affecting how you store water. Purchasing bottled water is a good way to start for small places with small amounts of storage. Bottled water is can be very expensive if you want to store a lot of water (more than 72hrs).

The next option is a larger container designed holding water. These containers are available is almost every size. If you can’t find the size you want in a store, there are companies that can make custom shapes and sizes. There are very few limits to the type of container. I mentioned earlier that the container needs to be designed for water. This is for two reasons. First, not all plastics are created equal. Some plastics can leach harmful chemicals like BPA into the water. The best type of plastic is high density polyethelene (HDPE).  HDPE is used on all sorts of applications, including water/chemical tanks and watermains.  Look for the symbol of a triange made of arrows around the number 2 and the letters HDPE underneath to make sure it is the correct one.

HDPE Symbol (source: termoplasticos.com)

Second, water is heavy. One liter of water weighs one kilogram (2.2 pounds). If the container isn’t designed for water there is a good chance it will break. For example a rain barrel holds around 400L, that barrel full of water will weigh over 400kg (or approximately 881lbs).  Below is a photo of a 1000L container, when full this container weighs one metric tonne (1000kg or 2204lbs).  The surface under this container needs to be secure and able to support the weight.  You also need to factor this weight into the support for the container and the shelving unit you store the water on.

1000L or 275 Gal Tote Excellent for Storing Water (source: http://www.theoldbarrelhouse.com)

Larger tanks need to be air tight. Otherwise the water remains open to contamination. Read here to learn what to do when your back up source of water becomes contaminated. The access point if it is on the top also needs to be air tight when closed. The access point needs to be raised above the rest of the tank so no water/cleaners/dust flows into the tank. If the water does become contaminated, read What to do when your back up supply is contaminated.  The tank will also need a spigot for accessing the water in the tank. The spigot should be installed just above the bottom of the tank (like it is in the picture above). Keeping the spigot just off the bottom avoids drawing any sediment that has settled on the bottom of the tank. Raising the spigot also makes it easier to fill containers.

There is are many theories for what kind of container is best. One big one or many little ones or a combination of sizes. This is a decision everyone needs to decide for themselves.  The general theory for using small bottles is that you can rotate your supply and if a small container becomes contaminated or leaks then you still have a safe supply in other bottles.  The general theory in support of large containers is that you can store a lot more water. You can also put pumps into large tanks an pump water to other areas.  With a pump and some tubing you can have a back up plumbing system or pump directly into your existing plumbing.

Now for the big question, how much water do you need to store?  According to the USGS, the average American household uses 80 to 100 gallons per person of water a day (302 to 378 L/person/day).  Now this is for ALL uses, many of which are in our appliances like dishwashers and washing machines.  But if you want everything to be EXACTLY as normal, then 100 gallons per person per day is what you need to store.  A family of four, will need 400 gallons/day and most emergencies are longer than one day.  This will quickly become an unreasonable amount of water to store.  This is where water conservation comes in.  Using less water makes your supply last longer.  I can’t give you a minimum storage volume.  The minimum amount of water that a human needs is variable on too many factors, like age (seniors and babies need more), climate, external temperature (hot and cold), altitude, health conditions, illnesses, type of disaster (some require a lot more washing), pregnancy, activity level, existing hydration levels and this list can be a lot longer. I will say this, having more water than you need is better than not having enough.  Listen to what your local authorities are recommending you store for your area and treat that as a minimum.  The correct answer of how much water to store is in between the 100 gal/person/day and the minimum recommended for your area and time of year.

I hope this article helped you understand a little more about the importance of storing water and a lot more on how to get your water supply started.  Everyone’s water storage solution is unique to them.  Balancing space and money mean that you will have to develop a system that works for you.

Water Survival During the Zombie Apocalypse

First off a bit of a disclaimer, I am fully aware that zombies are not real.  I am however highly entertained by zombies and all things undead.  Since the Omega Man Journal is about water and survival, that lead to the obvious thought experiment of what challenges a zombie outbreak would have on our ability to get safe drinking water.

Zombie, Zombies, Undead, Scary Zombie,

Zombie Rage Face (zombieambience.com)

The first thing to appear after the dead rise will be panic. Fear will be rampant and many people will be operating on their fight or flight instincts others will be holed up at home. This includes the people who work at municipal water treatment plants. Water facilities, although automated still depend heavily on people to operate them. When those people stop going to work or are already zombie chow then the water will stop shortly thereafter. To see what it would look like when a water system gets shut down and roughly how long it would take read Grid Shutdown: How Long Will The Water Last. The same will be true of the sewage systems. Read Grid Shutdown: Why Is There S#!t In My Basement, Sewage Emergency: Thunder Bay Flooding and A City Without Sanitation to see just how disgusting our once clean (or not so clean) cities will become.

Zombie, Horde, Zombie horde, the walking dead, set pictures

Zombie Horde (geektyrant.com)

Speaking of sanitation, people will die from unsanitary conditions. That means dead bodies, not just zombies, but regular dead bodies. Cholera is an excellent example of a waterborne disease that is a direct result of decomposing animal tissues in a water supply. Thirst will drive people to the nearest supply of water, then many will die on the banks and contaminate the lakes and rivers. Remember at this point I’m not talking about zombie contamination of water sources. That’s coming up later. This is a real danger when thirsty people or animals die in water supplies.

Depending on how zombies are created there may be a serious water vulernability. There are already bacteria, viruses, parasites and other micro-organisms that use both water and human bodies as part of their natural life cycle. Typically we call the effect of these micro-organisms “water borne disease”. Also there are already parasites that can take control of other organisms even to the point of making the host suicidal. Specifically there is a fungus that will radically alter the behaviour of ants turning them into zombie ants. (read more about zombie ants).  We are talking about total control of the host for the benefit of the parasite. Finally there are countless micro-organisms and insects that thrive and depend on rotting flesh to survive either for food or as a vital part of a life cycle stage like maggots turning into flies.

Bacteria thrive on and cause decomposition of deceased organic matter

Those three characteristics which already exist, put a zombie making organism on the edge of being possible. Nature has already made all the organisms necessary to create a zombie, luckily for now the necessary skills are in different organisms and target different organisms. The problem is, if nature caused one organism to eat rotting flesh, it can teach another organism to do the same. Same thing with learning to disperse through water and to take control of other organisms.

Zombie Ant With Fungus Growing Out Of Its Head (nationalgeographic.com)

Let’s assume this is the cause of zombification, what then can anyone do to protect themselves? The good news is that modern water treatment is very good at removing and inactivating micro-organisms. The combination of chemically assisted filtration and disinfection should (if done correctly) remove 99.999% of micro-organisms. Depending on the size of this fictitious zombie bug/parasite/virus it might be possible to remove even more than 99.999% if it is on the large end of the size scale. If it is a virus, which is the smallest type of micro-organism then removing 100% of the z-virus will be next to impossible. That means we better hope that there is a disinfection method that can kill the virus either chlorine, UV, ozone or boiling.

Zombies Again (beyondhollywood.com)

One thing many people haven’t thought about when they are talking about zombies and water.  Water is very heavy.  If you have to haul water from its source to your secure facility it will become very difficult to run at the same time.  Now vehicles are an option as are hand carts and if you have the resources pumps and pipes are best.  Just remember that they are all noisier and may attract unwanted attention from nearby zombies.

Those are some of the challenges I see affecting our ability to drink safe potable water in the event of a zombie outbreak.  I tried to be as true to real science as is possible when talking about zombies.  At the very least I hope you were entertained.  Can you think of anything I missed?

Grid Shutdown: Boil Water Advisory

If you have ever had a water main break on your street or any other service disruption to your water supply you may have experienced a Boil Water Advisory or a Boil Water Order. Boil water advisories/orders are the official response from the people running the water system. Below is a brief description of when a system would issue a boil water advisory or order and some general ideas for what should and should not be done as someone under a boil water advisory/order.

Source: districtgov.org

The good news about a boil water advisory is that they are often issued as a precautionary measure. Meaning they are often used in cases where the water isn’t actually dangerous. The system operators issue the warnings so they have done the proper due diligence. The liabilities involved if someone gets sick or dies and the public wasn’t informed are huge. Ok, at this point you may be wondering what sort of situations would require a boil water advisory. Typically any time there will be work on the distribution system requiring lowering the pressure or if the disinfection of the water system is interrupted for a long time.

Boil water orders are more serious. They come into place when large and persistent problems occur. Things like contamination of the source water and major failure of critical treatment equipment can cause boil water orders.

Boil Water Notice From The Regional District Of North Okanagan (source: vernonblog.blogspot.com)

The first thing you should do when you learn about a boil water advisory or order is read the information given to you. It will have instructions for you. It will have essential information for you like the cause if it is known and the expected duration. It will also list acceptable uses of the water, you might need to boil before drinking but washing is fine. Or you may not be able to use the water for gardening if the reason is due to chemical contamination. If you actually read the notice you will appear to have inside knowledge because in my experience very few people will ever read them. It will also list sources for alternative drinking water supply. Watch how fast the corner store sells out of water. In my experience, people only let this happen once. Then they start keeping a supply.  The written notice will usually only talk about “drinking” but the list of activities that require boiled water include food preparation, coffee makers (some don’t boil the water long enough or hot enough), brushing teeth, making ice, making infant formula and anything going into an immune compromised person.  Veterinarians also recommend that any water given to a domesticated house pet should also be boiled.  Livestock are a different story.  Anything that is already free range is already drinking untreated water and will probably be unaffected by drinking the unboiled water.  However, there is still a limit for bacteria concentrations in water consumed by livestock, free range or not, just like there is for every other animal (including us) on the planet.  Here is a link to the standards for water uses for the Province of British Columbia, use table 1 as a guidline for how to use water during a boil water advisory or boil water order.  If table 1 says “no applicable standard” then it is safe to use the unboiled water. http://www.env.gov.bc.ca/wat/wq/BCguidelines/microbiology/microbiology.html#toc

The biggest thing you should not do is abandon drinking tap water in favor of bottled water. This is a mistake. If you do this you are still at risk but you are significantly less likely to hear about it if something is wrong. Another thing to avoid doing is panic. This is one of those things where no news is good news. I tell the people that if you stop seeing me and hearing from me then everything is back to normal. This is because I am legislated to tell the public when there is a problem. At this time I also tell them the time line as does the written notice. After two consecutive clean water tests the system and water return to normal. It is also way too time and cost prohibitive to go back door to door and say “everything is fine now”.
If you live in a large city, there will probably be some media coverage of the return to normal situation. Otherwise if you don’t hear anything. After the date on the notice your water is fine. If there is still a problem they are legally required to tell you again about the problem.  Neither a boil water advisory or boil water order is something to panic about it is not time to call a well driller and go off the water system completely (if that is even an option where you live). It is time to start using your preparations and your backup water supplies.

If you don’t want to or can’t boil your water then you can always use an alternative form of disinfection.  Either ultraviolet radiation, sodium hypochlorite or calcium hypochlorite are acceptable alternatives.  Be careful of using these alternatives for highly turbid water sources.  The floating debris in the water can hide pathogens, cryptosporidum is highly resistant to chlorine as is girarda adding enough chlorine to kill these two microorganisims will make the water unsafe to drink.  Turbidity can also react with the chlorine to form hazardous chemical byproducts. Remember turbidity is removed from the water by setteling and filtering before disinfection to avoid these two problems. You may want to install a water filter in your home or purchase a portable water filter as a backup.

All that is left is what needs to be done after the boil water notice or order is lifted and everything returns to normal.  Flush all water-using fixtures like faucets and showers for at least one minute. Drain and flush all ice-making machines in your refrigerator. Run water softeners through a regeneration cycle.  Drain and refill hot water tanks set below 45 C (normal setting is 60 C). Change any filters either under sink style, on the faucet style and the ones in a jug in the refrigerator, regardless of the type of filter.  Filters that are designed for untreated water will not need to be changed unless they are used up.

Disinfection Of Water Using Ultraviolet Radiation

Ultraviolet light is a very popular method of disinfecting water.  UV radiation is part of the electromagnetic spectrum that has incredible properties for the killing of microscopic organisms.  While there are varying degrees UV resistance within microscopic organisms, not one has yet been able to develop a total resistance.  Because UV disinfection systems are not chemical or biological they have an extremely long shelf life.

The Electromagnetic Spectrum with a UV Focus (From: agtuv.com)

There is a wide variety of ultraviolet disinfection systems that range from the size of a pen to large banks of meter long light bulbs and many options in between. UV systems tend to be very simple to install and operate and UV leaves nothing behind and there are no disinfection by-products from its application.  In fact ultraviolet radiation can break down some potentially harmful chemicals like chlorine and chloramine compounds.

Ultraviolet Lamp (from: halmapr.com)

The limitations of UV disinfection are; distance, time, turbidity and electricity.

Proximity is critical for UV disinfection, the water needs to be very close to the UV light source. The farther away the water is the more radiation is absorbed by the water. Meaning that with increasing distance you get weakening disinfection.  Proximity becomes even more critical in hard water.  Hard water sources leave a white chalky residue of calcium carbonate which covers the UV light bulb, making the radiation emitted significantly weaker.

Time is another significant limitation of UV disinfection. The amount of time pathogens spend in the UV greatly affects whether or not the pathogen is neutralised. This is similar to how people get worse sunburns the longer they are exposed to the sun.  Time is directly related to the flow of the water, if the flow is too much, the water will not spend enough time exposed to the radiation and will not be disinfected.  Slow moving water or even static water is best.

The efficiency of UV disinfection is greatly reduced by turbidity. Turbidity physically shields the organisms from the UV light. Exactly the way a beach umbrella shades people from the sun. This is called line of sight disinfection.  There is no disinfection in the shadows when using UV radiation.

Electricity is another limitation of UV disinfection systems.  They are limited in two ways by electricity.  First by the fact that  they are quite literally light bulbs placed underwater and secondly by fluctuations in the electrical source cause fluctuations in the UV radiation field emitted from the bulbs.  Both these problems are easily overcome.  By sealing the system in clear waterproof chambers can effectively keep the system safe from the water.  Fluctuations in the electrical source can be minimized through proper system design and using fresh/charged batteries in battery powered systems.

SteriPen Portable Ultraviolet Disinfection (from wikipedia.org)

Portability is a mixed blessing with UV disinfection systems. Smaller, pen-like devices are easy to transport, but are significantly less powerful. That means they need to be used on slower moving/still water and used for longer than larger UV systems.  Another mixed blessing of ultraviolet disifection is the fact that there is no disinfection residual left in the water.  Not having a disinfection residual is great if you are drinking the water immediately, otherwise recontamination can occur very quickly after the UV lamps are shut off.  UV is not enough if you plan on storing the water for a long period of time.

Recirculating the water to be disinfected a second or third time will greatly increase the chances of proper disinfection.  Remember that disinfection whether by UV or chlorine or any other method is one of the final stages of water treatment.  Forgetting to filter the water first will make disinfection significantly more difficult.  Regardless of the size of the of the system used, ultraviolet radiation can be used to supplement any water treatment process.