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What Contaminants are in River Water?

In order to make raw water safe to drink, we need to first understand what dangers the water source holds.   Whether treating water in the backwoods or in a modern industrial Drinking water treatment facility, the steps needed to clean and purify water depend on the contaminants in the source.  

The United States Environmental Protection Agency (EPA) is the regulatory body charged with defining the effluent quality needed for municipal and commercial water treatment.  These limits are often expressed in terms of milligrams per liter of water, levels far below what we can hope to achieve with improvised treatment methods, but they can help guide us in understanding what kinds of dangerous contaminants occur.  To put it plainly, we will not be able to make water totally safe in the backcountry, only make it less unsafe.  

The EPA has two sets of drinking water standards, primary and secondary. 

Primary vs Secondary Drinking Water Standards

Primary drinking water standards are mandatory, for the protection of health and safety.  Secondary standards are recommendations to help control odor, taste, and prevent undue wear on pumps and other machines. 

Water that meets all primary standards is “safe to drink”, per the EPA, even if it does not comply with all secondary standards.  This water could taste, look, and smell terrible, but still be safe.  On the other hand, water that looks and tastes wonderful could be very, very dangerous if it meets all the secondary standards, but fails to meet even one of the primary ones. 

However, our senses can still be helpful, as many biological contaminants do make water look cloudy and smell awful.  In general, clear, fast-moving water will be of better quality than smelly stagnant water, but it should still undergo at least some treatment.

The primary drinking water standard contaminants are divided up into six categories: microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, and radionuclides.  Many of these are undetectable without special equipment, even at dangerous concentrations.


Microorganisms include cryptosporidium, giardia, legionella, and E. Coli as directly limited, as well as controls on the total turbidity (water cloudiness) as an indirect control on the many other detrimental microorganisms.  In fresh surface water sources like lakes and streams, microorganisms are the most likely contaminant, and as such will be our major focus.  Microorganisms are only harmful when present and alive in drinking water.  Filtration (through a fine enough filter) and settling can remove them from the water, or they can be killed off with heat, Chemical disinfectants, or enough exposure to ultraviolet radiation (like sunlight).

Disinfectants and Byproducts

Chemical disinfectants like chlorine or iodine are molecular poisons.  They excel at killing off microorganisms, but are also hazardous to human health, so limits exist on their concentrations when the water leaves the treatment plant for the distribution network. 

Unfortunately, the byproducts of chemicals like chlorine tearing microbes apart are also dangerous, though in a less immediate sense than Legionnaire’s Disease. 

“Trihalomethanes”, methane with three of the hydrogen atoms replaced with chlorine or other halogen atoms, have been recognized as causing cancer. 

No one wants to drink carcinogens, so disinfection byproducts are limited as well.  These are unlikely to be encountered in the backcountry, but could well be found downstream of overzealous water and wastewater treatment facilities.

Chemical disinfectants rarely occur naturally, but can be introduced into water by some industrial and agricultural activities.  The most likely source in the backcountry is those awful iodine tablets.  They don’t just smell and taste bad, they actually leave behind residuals that can have adverse health effects, though properly following the instructions with the neutralizing tablet helps limit them. 

Disinfectants are normally reacted out of the water chemically, placing them firmly outside the scope of the average improvising outdoorsman or outdoorswoman.  None of the techniques discussed in later chapters will be very effective in their removal, short of full-on distillation operations, or the limited success that can be had from adsorption.

As a side note: Some small amount of chlorine is typically left in US municipal water to kill off any microbes that make their way into the pipes.  In much of the European Union, disinfection of drinking water is instead accomplished by running the water under extremely bright ultraviolet (UV) lights, and no residual disinfectant is added.  B

oth approaches have their drawbacks, as the “purer” European water is much more vulnerable to microbes that may infiltrate the distribution system, while the American chlorinated water will transform those microbes into carcinogens.  This may help explain the higher occurrence of Legionnaire’s Disease in Western Europe, versus the higher cancer rate in the US.

Inorganic Chemicals

The inorganic chemicals group is made up of arsenic, heavy metals, and nitrates/nitrites.  For the most part, these will be difficult to detect on your own unless they are present in very high concentrations.

Side Note: I once lived in a house with well water that was very high in nitrates, and once the water was softened, it smelled like a cured ham.

Heavy metals and arsenic are usually leached out of naturally-occurring deposits that the water interacts with, either over veins on the surface, or permeating through subsurface deposits.  Nitrates and nitrites tend to occur from fertilizer runoff. 

Most of these are tough to recognize on your own, but the good news for survival situations is that many of them take time to build up to toxic levels.  They *hopefully* won’t do you in as quickly as massive dehydration brought on by dysentery, which is helpful, as options for dealing with them in the backcountry are very limited. 

Avoidance is the preferred method, but distillation can work for many of them, as well as adsorption to a limited extent.

Organic Chemicals

Organic chemicals, like benzene and PCBs, are usually introduced to water sources by industrial or agricultural operations.  Proper removal requires a laboratory and some knowledge of organic chemistry, so we won’t go very deep into them. 

Some fall into the category of Volatile Organic Compounds (VOCs), and give off very strong odors that can warn of their presence, but others are stealth killers.  Usually not a concern unless there is heavy industrial/agricultural activity in the area, avoid drinking from water sources downstream of mining operations especially.  Some of these can be driven off by boiling, as they have a lower boiling point than water, but not all.  Some can also be adsorbed by activated charcoal.


The final category, radionuclides, is the scariest of the bunch.  Without a Geiger Counter, you will have no idea they’re present, but in high concentrations or prolonged exposure to low concentrations, they’re still quite lethal.  Caused by water flowing over and around natural deposits of uranium and the like, our only hope is avoidance. 

Get to know the geology of your preferred outdoor recreation area.  Make a point of avoiding areas with large deposits of uranium and other radioactive ores (usually a good idea in any case), and surface water sources will be unlikely to pose much threat. 

However, many more groundwater sources have high levels of radionuclides, so be aware of the threats in your area.  A friend from New Hampshire mentioned that up that way it’s common practice to have regular testing of any private well tap water.

Salt Water

Additionally, it’s not a good idea to drink salt water.  Though not specifically listed in the primary drinking water standards above, drinking salt water will kill you more quickly than water contaminated with many of the contaminants we’ve already talked about. 

Your body will suck pure water out of your cells to try to dilute down the salts in seawater, which will dehydrate you very quickly.  Kidney failure is also quite common with seawater ingestion cases, as the kidneys go into overdrive trying to filter out the high concentrations of a whole trove of salts and minerals.  The best way to deal with the salt is some form of distillation.

Knowing Contaminants

Most outdoor enthusiasts don’t carry fully-stocked water quality test kits in the field, nor do we know how to do anything meaningful with them.  Our best way to be prepared is to be informed.  Ask around about the water quality issues anywhere you plan to spend some time, even if it’s just for a day trip. 

Many park rangers will be quite knowledgeable of the common contaminants in their area, and can even make recommendations on what filter mesh size is required to extract the most common microbes.  Pay attention in visitor’s centers, as many will have signs giving the same information.  The internet is also a treasure-trove of information for popular outdoor travel spots.

Limitations of Improvised Water Treatment

Keep in mind that water will almost never have just one contaminant or class of contaminants.  Seawater is rich in minerals and microorganisms.  Groundwater is much more likely to be contaminated with heavy metals and radionuclides.  Surface fresh water often has microorganisms of all sorts, and may have other issues as well. 

Conventional drinking water treatment consists of several stages designed to settle out sediment, filter out remaining small contaminants, and disinfect what’s left.  To this framework, many distinct auxiliary processes are added to neutralize the particular threats of the source water, such as pH adjustment, heating to remove VOCs, or chemical treatments to reduce chemical and radiological contaminants.  

Especially with improvised treatment methods, it’s important to use as many methods as feasible to ensure that the water is as clean as possible.  Filtered and boiled water can still be rich in arsenic and lead.  Each treatment method only works on some of the threats, and it’s impossible to know without testing exactly which threats were in the water to begin with.  We can only do our best with what’s available, and hope it’s enough.

Grab the Full Book!

This has been an excerpt from the chapter on Contaminants in my latest book on Drinking Water Treatment for Adventurers and Preppers.

If you’ve enjoyed it and want to learn more, grab the full book on Amazon today, available in both print and eBook formats!

This post first appeared on Ben Gordon Outdoors, please read the originial post: here

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What Contaminants are in River Water?


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