I mentioned here that getting clean potable water can be difficult in many parts of the Amazon, including the larger cities. In fact, I strongly recommend against drinking any untreated water in the Amazon, no matter how clear and tempting it might appear. And that includes rainwater, unless you know that the containers in which the water has been caught and stored have been properly cleaned and maintained.

Even when you get water through a pipe, the quality of the water depends on where the water comes from and whether the pipe has any cracks or leaks. In addition, the single most important cause of gastrointestinal illness in the wilderness is oral-fecal contamination from dirty hands. Sure, you wash your hands after using the latrine, but does everyone who handles your food and water?

So, if you are thinking of heading into the jungle, here are some survival tips.

There are three sorts of waterborne microorganisms that can cause human illness in the wilderness — viruses, bacteria, and protozoan cysts. Bacteria in contaminated water may include Escherichia coli, Shigella, and even Salmonella; protozoa may include Giardia and Cryptosporidium — all potential contaminants whenever animal or human fecal material gets into your water source. It is worth bearing in mind that just about any gastrointestinal infection you get from contaminated water can do more than just spoil your trip.

Apart from packing in your own bottled water, there are four ways of treating water in the jungle.

Boiling is completely effective against protozoan cysts, nontoxic bacteria, and viruses. Bringing the water to a rolling boil is enough, except at higher altitudes, where longer boiling is required because the water boils at a lower temperature. If you are backpacking, there is nothing extra to carry, since you have a pot and stove anyway. On the other hand, boiling takes time and uses up your fuel. Boiling also does not remove sediment, but filtering the water through a bandana usually takes care of that.

Halogens such as iodine or chlorine kill bacteria and viruses, but may not kill all protozoan cysts. Iodine tablets such as Potable Aqua and saturated iodine solutions such as Polar Pure are readily available, inexpensive, and lightweight. You can make your own water treatment kit by putting iodine crystals in the bottom of a small bottle, filling it with water, and using capfuls of the resulting saturated iodine solution to treat your drinking water. If you just keep refilling the bottle with water, the iodine will last indefinitely.

Some people dislike the iodine taste of treated water, but the taste can be eliminated by adding some vitamin C, as in powdered fruit drinks; in fact, the Potable Aqua “taste neutralizer tablets” are simply ascorbic acid. Another drawback is that the halogen must be given time to work before you can drink the water — anywhere from fifteen minutes to an hour, depending on how cloudy or cold the water is. Pregnant women and people with thyroid conditions may have adverse reactions to iodine.

Mechanical filtration forces the water through a finely porous internal element inside the case in order to physically strain out solid materials, including fine sediment and most — but not all — microorganisms. Bear in mind the difference between a filter and a purifier. A filter mechanically removes protozoa and bacteria from contaminated water. A purifier goes a step further and eliminates viruses as well, by passing the water through either a matrix containing iodine, which kills them, or a filter medium that carries an electrostatic charge, which traps them. A device must inactivate 99.99 percent of viruses to be labeled as a purifier.

There is spirited debate about the relative merits of filters and purifiers. Portable filters and purifiers are compact, relatively speedy, efficient, and you can drink the water immediately. On the other hand, they are heavy, a chore to operate, occasionally cranky, and easily become clogged with sediment.

Ultraviolet light, if strong enough and applied long enough, destroys the DNA of microorganisms, making them unable to reproduce and cause illness. A small portable ultraviolet light source, weighing less than four ounces, called the SteriPEN Adventurer is designed to be inserted into a wide-mouth water bottle, and is supposed to take about fifty seconds to purify sixteen fluid ounces and about ninety seconds for a liter. It is said to be effective against viruses, bacteria, and protozoa, and it leaves no iodine taste.

A drawback is that the device is operated by batteries, and batteries require recharging or replacement, which may not be feasible in wilderness conditions; and the device’s performance is significantly affected by the quality of the batteries used. You can get the device with a solar panel battery charger storage case, but it can take two to five days to recharge two cr123 batteries, depending on sun conditions. The device does not remove sediment, but, as with boiling, you can prefilter with a bandana.