You know you need to filter, treat or boil water you find in the wilderness. But why? Well, there's a number of answers, starting with words like E. Coli, Hepatitis A, Giardia and Cryptosporidiosis.

Let's look at some common sources of waterborne diseases/infections/stuff that will give you the shits, examine what they are, what they do to your body and, lastly, how you can avoid getting them in your system.

Protozoa

Protozoa are little single-celled critters and the relevant ones to this discussion are parasites. The two most common of those you'll encounter outdoors are Giardia and Cryptosporidium.

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Giardia is much more common and is said to be found in literally every single body of water in the United States. Its source? Poop. From us and other animals. If you get some in you, it'll spend two to three days building up in your body, then you'll get messy case of the runs sometimes accompanied by extreme amounts of gas and stomach cramps. In most cases, it'll clear up on its own, but in immunosuppressed sufferers it can lead, in some extreme circumstances, to your small intestine atrophying. Treatment is easy with a prescription vermicide; if you think you've got it, see your doctor.

Cryptosporidium also has a two to three day incubation period and then leads to Cryptosporidiosis or just "Crypto" to most folks. It's also spread through poop in water and also leads to cramps and diarrhea. But, it's also a more serious disease that can lead to pancreatic or, in an immunosuppressed person, severe, cholera-like symptoms. In AIDS patients, it's been shown to spread to other organs beyond the intestines including the lungs and ears and can lead to death.

Prevention: You kill Giardia with a simple iodine treatment and it's taken out by most filters. Crypto is more persistent, requiring chlorine dioxide to kill it. Most filters aren't capable of removing it from water, the popular Aquamira tablets and drops are. To be safe, boil any water you're worried about. According to the CDC, there's 748,000 cases of crypto in the US each year.

Photo: Phil Moyer

Bacteria

There's a whole host of bacteria that can get into a water source from poop, decaying corpses of dead critters or even just rotting vegetation. Escherichia Coli being the most common.

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The potential effects of E. Coli vary (and it already exists in your gut!), but the Mayo Clinic says it can cause diarrhea, cramping, abdominal pain, nausea and vomiting. If you think you've been exposed, then hydration is your first goal and you may need prescription antibiotics if the infection is severe.

Prevention: Luckily, it's easy to kill. Treating your water with iodine, tablets, drops, filters, UV pens or even day-long exposure to sunlight in a clear bottle will do the job.

Photo: Microbe World

Viruses

Spread again through poop in water, Hepatitis A is the most common virus you'll encounter outside. Symptoms can take two to six weeks to appear and include your typical diarrhea and vomiting, this time accompanied by yellow skin, a fever, joint pain and cramps.

Treatment is usually just a case of you being sick for a few days, drinking a lot of liquids, acting like a total wuss and then getting over it.

Prevention: There's a vaccine which, if you're traveling to a gross part of the world, is a really good idea. And, if you get it once, you become immune. The CDC says treatment with iodine or chlorine dioxide or boiling are the most effective ways to kill viruses in water.

Chemicals

Pollution. This can run from heavy metals to toxic sludge to just runoff from roads — gas and oil and soot and all sorts of nastiness. Symptoms will range from your usual diarrhea and cramps to growing a third eye or dying.

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Not drinking nasty polluted water is the best way to avoid becoming a CHUD. Consider your water source. Does a river flow down towards you from a chemical plant? Maybe don't drink that. Same goes for roads, cities, farms, and pretty much any other form of human civilization.

Prevention: The only way to remove chemicals from water is to evaporate the water and capture the steam. A solar still can do this and is also capable of producing potable water from the ocean. But doing that takes a lot of time and effort, which is probably better spent just finding a better water source.

The Real World

I've been drinking water largely untreated my entire life, and been going camping my entire life. In those 34 years, I've gotten Giardia once. And that was from a nasty water source in a high traffic area with visible trash and which was stagnant and nearly dried up during the Southern California summer. In short, I should have remembered my damn iodine. The infection manifested itself a few days later with a moderate case of diarrhea that lasted less than a week. It was a worse case of diarrhea than you'd get from, say, a bad meal from a crappy restaurant, but it was largely manageable.

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Should you filter your water? Absolutely. But, if you come across a natural spring and just want to see what it tastes like right out of the ground or, if you're stuck out somewhere without a good means of doing so, use some common sense and don't be too afraid to just drink the damn water already. You'll die from dehydration much faster than you will from an infection.

Top photo: Proyecto Agua

IndefinitelyWild is a new publication about adventure travel in the outdoors, the vehicles and gear that get us there and the people we meet along the way. Follow us on Facebook, Twitter and Instagram.