A Solar Still is a device that can be constructed in order to distill contaminated water into drinking water, or to pull condensation from damp resources in order to produce enough water for consumption. Solar stills can be a life-saving device if stranded in the desert without water or if lost at sea. This simple device uses the sun to evaporate contaminated water from a collection basin and collect the condensation in another basin. The condensation is essentially distilled and drinkable. It can be done with saltwater and can even be constructed to pull moisture from the ground if water isn't available at all. Solar stills can either be constructed out of simple materials or purchased and used for emergency. To learn how to make a solar still in a survival situation or to purchase one in case of emergency, read our detailed article about solar stills here.
Permanent water chlorination began in 1905, when a faulty slow sand filter and a contaminated water supply led to a serious typhoid fever epidemic in Lincoln, England.[44] Dr. Alexander Cruickshank Houston used chlorination of the water to stem the epidemic. His installation fed a concentrated solution of chloride of lime to the water being treated. The chlorination of the water supply helped stop the epidemic and as a precaution, the chlorination was continued until 1911 when a new water supply was instituted.[45]
Ultraviolet light (UV) is very effective at inactivating cysts, in low turbidity water. UV light's disinfection effectiveness decreases as turbidity increases, a result of the absorption, scattering, and shadowing caused by the suspended solids. The main disadvantage to the use of UV radiation is that, like ozone treatment, it leaves no residual disinfectant in the water; therefore, it is sometimes necessary to add a residual disinfectant after the primary disinfection process. This is often done through the addition of chloramines, discussed above as a primary disinfectant. When used in this manner, chloramines provide an effective residual disinfectant with very few of the negative effects of chlorination.
Disinfection is accomplished both by filtering out harmful micro-organisms and by adding disinfectant chemicals. Water is disinfected to kill any pathogens which pass through the filters and to provide a residual dose of disinfectant to kill or inactivate potentially harmful micro-organisms in the storage and distribution systems. Possible pathogens include viruses, bacteria, including Salmonella, Cholera, Campylobacter and Shigella, and protozoa, including Giardia lamblia and other cryptosporidia. After the introduction of any chemical disinfecting agent, the water is usually held in temporary storage – often called a contact tank or clear well – to allow the disinfecting action to complete.
It occurred to me that chlorine gas might be found satisfactory ... if suitable means could be found for using it.... The next important question was how to render the gas portable. This might be accomplished in two ways: By liquefying it, and storing it in lead-lined iron vessels, having a jet with a very fine capillary canal, and fitted with a tap or a screw cap. The tap is turned on, and the cylinder placed in the amount of water required. The chlorine bubbles out, and in ten to fifteen minutes the water is absolutely safe. This method would be of use on a large scale, as for service water carts.[49]
Large-scale industrial/municipal systems recover typically 75% to 80% of the feed water, or as high as 90%, because they can generate the high pressure needed for higher recovery reverse osmosis filtration. On the other hand, as recovery of wastewater increases in commercial operations, effective contaminant removal rates tend to become reduced, as evidenced by product water total dissolved solids levels.
What many poor people, backcountry hikers, and those living in remote areas have in common are a reliance on untreated, local sources of water that may be contaminated, and must be purified before it can be safely consumed. There are two basic approaches to water purification: using a reverse osmosis filter, or a tag team of two methods working together to eliminate two separate contaminants.
Chlorine dioxide is a faster-acting disinfectant than elemental chlorine. It is relatively rarely used because in some circumstances it may create excessive amounts of chlorite, which is a by-product regulated to low allowable levels in the United States. Chlorine dioxide can be supplied as an aqueous solution and added to water to avoid gas handling problems; chlorine dioxide gas accumulations may spontaneously detonate.

Prefiltration antiscalants: Scale inhibitors (also known as antiscalants) prevent formation of all scales compared to acid, which can only prevent formation of calcium carbonate and calcium phosphate scales. In addition to inhibiting carbonate and phosphate scales, antiscalants inhibit sulfate and fluoride scales and disperse colloids and metal oxides. Despite claims that antiscalants can inhibit silica formation, no concrete evidence proves that silica polymerization can be inhibited by antiscalants. Antiscalants can control acid-soluble scales at a fraction of the dosage required to control the same scale using sulfuric acid.[23]


When particles to be removed do not settle out of solution easily, dissolved air flotation (DAF) is often used. After coagulation and flocculation processes, water flows to DAF tanks where air diffusers on the tank bottom create fine bubbles that attach to floc resulting in a floating mass of concentrated floc. The floating floc blanket is removed from the surface and clarified water is withdrawn from the bottom of the DAF tank. Water supplies that are particularly vulnerable to unicellular algae blooms and supplies with low turbidity and high colour often employ DAF.[6]:9.46
It isn’t the most affordable system, but it does reduce wastewater compared to many other systems. For every 1 gallon of purified water, there is just 1 gallon of wastewater, thanks in part to the permeate pump. Maintenance is easy for this reverse osmosis system—you’ll only need to change the filter once per year or every 2,000 gallons. So pour yourself a glass of clear, clean water and drink with peace of mind thanks to the Home Maker Full Contact Reverse Osmosis System!
Within the United States Marine Corps, the reverse osmosis water purification unit has been replaced by both the Lightweight Water Purification System and Tactical Water Purification Systems.[14] The Lightweight Water Purification Systems can be transported by Humvee and filter 470 litres (120 US gal) per hour. The Tactical Water Purification Systems can be carried on a Medium Tactical Vehicle Replacement truck, and can filter 4,500 to 5,700 litres (1,200 to 1,500 US gal) per hour.[citation needed]
It occurred to me that chlorine gas might be found satisfactory ... if suitable means could be found for using it.... The next important question was how to render the gas portable. This might be accomplished in two ways: By liquefying it, and storing it in lead-lined iron vessels, having a jet with a very fine capillary canal, and fitted with a tap or a screw cap. The tap is turned on, and the cylinder placed in the amount of water required. The chlorine bubbles out, and in ten to fifteen minutes the water is absolutely safe. This method would be of use on a large scale, as for service water carts.[49]
Water Waste Unlike traditional water filters, not all of the water that is pumped through a reverse osmosis filter comes out the other side as drinkable water. Only a relatively small percentage—50 percent or less—is filtered, and the rest is considered waste. When possible, avoid units with 75 percent or more waste, especially if you are treating a high volume of water per day.
A reverse osmosis filter is the do-it-all of water purification. The process is the only one that addresses both harmful microorganisms and pollutants at the same time. It works by forcing water under pressure through a membrane made of thin film composite, with a inner matrix of dense polymers. The result leaves purified water on one side of the membrane, and contaminants on the other side. The technology is reliable, but expensive and relatively cumbersome, and requires electricity to work. It is therefore a sound choice for use in fixed positions or by those who can afford to tow a small trailer with a small electrical generator around, but anyone on the move or without access to electricity needs to use other methods.
In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (high water potential), through a membrane, to an area of high solute concentration (low water potential). The driving force for the movement of the solvent is the reduction in the free energy of the system when the difference in solvent concentration on either side of a membrane is reduced, generating osmotic pressure due to the solvent moving into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications.
Photo by purolipanFor flexibility, a good multi-tool is a camper’s best friend, and there are hundreds of models on the market. When comparing the need for different functions and the tool’s weight, it becomes apparent that simpler is better. Look for a multi-tool that has a regular and serrated blade, pliers with a wire cutter, carbide knife sharpener, bottle and can opener, and a lanyard loop. Pay close attention to the materials and quality; look for titanium handles, 154CM steel blades, and 420 stainless steel construction. If you plan on carrying a small hatchet for cutting firewood, consider a multi-tool hatchet and take one tool instead of two.

DO: Avoid shark-infested waters, unless you are Andy Casagrande. As for bears, always carry repellent pepper spray when hiking; it can stop a charging bear from as much as 30 feet away. To reduce the risk of an attack, give bears a chance to get out of your way. "Try to stay in the open," says Larry Aumiller, manager of Alaska's McNeil River State Game Sanctuary. "If you have to move through thick brush, make noise by clapping and shouting."


Water, apart from shelter, can become the most immediate need in a survival situation. Drinkable water is a vital resource. Depending on the level of activity, and ambient temperature, a person can live about 3 days without water. Prolonged activity without proper hydration coupled with malnutrition will quickly lower chances for survival. Finding a way to create and maintain a source of clean drinking water is essential for both short and long term emergency preparedness. Whether you find yourself lost in the wilderness or in an urban emergency scenario such as Katrina and Toledo's water crisis, water is life. Just one day without this precious fluid and we begin to see the symptoms of dehydration.
Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc.
The other half of the tag team is to eliminate pollutants. The best way to do this is with a homemade carbon filter. This uses the same technology as Brita filters. Carbon is a chemically active substance, with a tendency to bind to most anything. At a microscopic level, charcoal is a heavily pitted and striated material, which vastly increases its real surface area. The result is that when water slowly runs over charcoal, pollutants find themselves glued to the charcoal surface. An improvised filter can be made out of ground-up charcoal, a strainer and a funnel. Bear Gryllis made a purification drinking straw out of little more than a reed and some charcoal bits for the Discovery Channel's "Man vs. Wild." It's a simple technique, but it is highly effective.

Only a part of the saline feed water pumped into the membrane assembly passes through the membrane with the salt removed. The remaining "concentrate" flow passes along the saline side of the membrane to flush away the concentrated salt solution. The percentage of desalinated water produced versus the saline water feed flow is known as the "recovery ratio". This varies with the salinity of the feed water and the system design parameters: typically 20% for small seawater systems, 40% – 50% for larger seawater systems, and 80% – 85% for brackish water. The concentrate flow is at typically only 3 bar / 50 psi less than the feed pressure, and thus still carries much of the high-pressure pump input energy.
The pore size of the filter, usually measured in microns, will determine what will be filtered through. While a standard micron size of 0.2 is small enough to block heavy metals such as lead and copper and large parasites such as Cryptosporidium, it will not block viruses. The National Sanitation Foundation sets a standard for effective water filtration products so look for an NSF stamp when selecting a filter to purchase.
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