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]

A specific "large-scale" form of slow sand filter is the process of bank filtration, in which natural sediments in a riverbank are used to provide a first stage of contaminant filtration. While typically not clean enough to be used directly for drinking water, the water gained from the associated extraction wells is much less problematic than river water taken directly from the river.

My old RO filter (with UV) was not working right, even after replacing all the filters. So I was looking for a new RO system with good reviews and decided on 2 systems: Tap Master TMAFC Artesian Full Contact Reverse Osmosis with Alkaline by Perfect Water and iSpring 6-stage with RO Alkaline. The Tap Master had tons of great feedback, but so was iSpring (the non-alkaline model). The only reason why I ended up purchasing iSpring was the price.
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.
In 1904, Allen Hazen showed that the efficiency of a sedimentation process was a function of the particle settling velocity, the flow through the tank and the surface area of tank. Sedimentation tanks are typically designed within a range of overflow rates of 0.5 to 1.0 gallons per minute per square foot (or 1.25 to 2.5 litres per square meter per hour). In general, sedimentation basin efficiency is not a function of detention time or depth of the basin. Although, basin depth must be sufficient so that water currents do not disturb the sludge and settled particle interactions are promoted. As particle concentrations in the settled water increase near the sludge surface on the bottom of the tank, settling velocities can increase due to collisions and agglomeration of particles. Typical detention times for sedimentation vary from 1.5 to 4 hours and basin depths vary from 10 to 15 feet (3 to 4.5 meters).[6]:9.39–9.40[7]:790–1[8]:140–2, 171
A process of osmosis through semipermeable membranes was first observed in 1748 by Jean-Antoine Nollet. For the following 200 years, osmosis was only a phenomenon observed in the laboratory. In 1950, the University of California at Los Angeles first investigated desalination of seawater using semipermeable membranes. Researchers from both University of California at Los Angeles and the University of Florida successfully produced fresh water from seawater in the mid-1950s, but the flux was too low to be commercially viable[4] until the discovery at University of California at Los Angeles by Sidney Loeb and Srinivasa Sourirajan[5] at the National Research Council of Canada, Ottawa, of techniques for making asymmetric membranes characterized by an effectively thin "skin" layer supported atop a highly porous and much thicker substrate region of the membrane. John Cadotte, of FilmTec Corporation, discovered that membranes with particularly high flux and low salt passage could be made by interfacial polymerization of m-phenylene diamine and trimesoyl chloride. Cadotte's patent on this process[6] was the subject of litigation and has since expired. Almost all commercial reverse-osmosis membrane is now made by this method. By the end of 2001, about 15,200 desalination plants were in operation or in the planning stages, worldwide.[2]
The ultraviolet rays of the sun can be extremely destructive to microorganisms. We as humans avoid it as much as possible as it can cause skin cancer and other diseases. But we have learned to harness its power and use it to our advantage, especially in decontaminating our water from harmful bacteria and pathogens. UV light has been a standard in the disinfection of water supplies at the municipal level for decades but has recently become available for home use.

The booster pump included with this tankless reverse osmosis system requires electricity but helps to maximize the efficiency of the system. It can achieve up to a 1:1 ratio of purified to wastewater. However, in real-world use, some people found that wastewater was more like 2 gallons for every 1 gallon of purified water produced. iSprings points out that many factors affect this efficiency rating, so some variance in results is to be expected.

The APEC Ultimate 6-Stage Reverse Osmosis system removes up to 99 percent of bacteria, contaminants, and solids. But it also adds back in calcium and magnesium, which are beneficial minerals for your health and improve the taste of drinking water. The system is rated for purifying up to 75 gallons per day, which is plenty for the average family’s daily needs. The system includes a flow restrictor and an automatic shutoff valve that help to reduce wastewater to 3 gallons for every 1 gallon of purified water produced. Some other systems produce in excess of 5 gallons of wastewater to every 1 gallon of purified water.
Like most under sink reverse osmosis systems, you’ll need to clear enough space for the 3.2-gallon pressurized storage tank and the filter cartridges. But once you do, you’ll find that the rest of the installation is easy according to most reviewers. One user mentions that they move every 3 years but are happy to uninstall and re-install the system in each new residence due to the high performance and easy set-up of the iSprings RCC7AK.
Pressure exchanger: using the pressurized concentrate flow, in direct contact or via a piston, to pressurize part of the membrane feed flow to near concentrate flow pressure. A boost pump then raises this pressure by typically 3 bar / 50 psi to the membrane feed pressure. This reduces flow needed from the high-pressure pump by an amount equal to the concentrate flow, typically 60%, and thereby its energy input. These are widely used on larger low-energy systems. They are capable of 3 kWh/m3 or less energy consumption.
Water conditioning: This is a method of reducing the effects of hard water. In water systems subject to heating hardness salts can be deposited as the decomposition of bicarbonate ions creates carbonate ions that precipitate out of solution. Water with high concentrations of hardness salts can be treated with soda ash (sodium carbonate) which precipitates out the excess salts, through the common-ion effect, producing calcium carbonate of very high purity. The precipitated calcium carbonate is traditionally sold to the manufacturers of toothpaste. Several other methods of industrial and residential water treatment are claimed (without general scientific acceptance) to include the use of magnetic and/or electrical fields reducing the effects of hard water.[20]

Iodine solutions kill bacteria by upsetting the ion balance within the cell, replacing chemicals that the bacteria needs to survive with iodide ions. Iodine can also be poisonous to humans, and can be especially harmful to young children, and pregnant women. You should be careful not to use too much iodine when purifying your water, and if at all possible avoid using it as a primary purification method for extended periods of time. If you find yourself in a survival situation, for an extended period of time, you should consider setting up a still, or boiling the water if possible.
There are multiple built in filters water bottles choices. Vestergaard's Lifestraw Go and Sawyers Personal Water Bottle are two examples. The Lifestraw Go filters specs say it will filter up to 1,000 liters (264 gallons) of water down to particulate matter larger than 0.2 microns Source Sawyer's Personal Water bottle absolute hollow fiber membrane inline filter down to 0.1 micron. Source
Desalination – is a process by which saline water (generally sea water) is converted to fresh water. The most common desalination processes are distillation and reverse osmosis. Desalination is currently expensive compared to most alternative sources of water, and only a very small fraction of total human use is satisfied by desalination. It is only economically practical for high-valued uses (such as household and industrial uses) in arid areas.

To clean the filter, water is passed quickly upward through the filter, opposite the normal direction (called backflushing or backwashing) to remove embedded or unwanted particles. Prior to this step, compressed air may be blown up through the bottom of the filter to break up the compacted filter media to aid the backwashing process; this is known as air scouring. This contaminated water can be disposed of, along with the sludge from the sedimentation basin, or it can be recycled by mixing with the raw water entering the plant although this is often considered poor practice since it re-introduces an elevated concentration of bacteria into the raw water.
Filter out pathogens with pine trees. Certain plants are effective at removing pathogens from water, and pine trees are among the best. To remove viruses and bacteria from your water, remove a small branch from a pine tree. Strip the bark from the stick and place the bare stick into a bucket. Slowly pour the water, letting it trickle onto the stick and into the bucket.[10]
The simplest levels of filtration can be achieved by running the water through a cloth. The tighter the weave of the cloth the better it will filter water, as it will be able to capture smaller/finer particles. Just about any cloth will catch the “big” stuff. Folding the cloth to form multiple layers will help in this process. If you are setting up a long term camp, you can set up a more intricate filtration system, that will not only filter particulates, but also improve taste.
Because the the semi-permeable membrane filters particles at the molecular level, reverse osmosis is extremely effective at removing bacteria, viruses, parasite cysts such as Giardia and Cryptosporidium, heavy metals such as lead and mercury, hard water minerals such as calcium and magnesium, and even fluoride and arsenic. It will not, however, remove certain pesticides and solvents small enough to pass through the membrane.

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
In addition to desalination, reverse osmosis is a more economical operation for concentrating food liquids (such as fruit juices) than conventional heat-treatment processes. Research has been done on concentration of orange juice and tomato juice. Its advantages include a lower operating cost and the ability to avoid heat-treatment processes, which makes it suitable for heat-sensitive substances such as the protein and enzymes found in most food products.
Use sedimentation. When you don’t have access to anything that you can use to filter the water, you can remove large particulate from water by letting it settle. Collect the water in a bowl or jar. Leave the water to settle for one to two hours. During this time, heavier particles will sink to the bottom, and lighter material will float to the top.[3]

Reverse osmosis is extensively used in the dairy industry for the production of whey protein powders and for the concentration of milk to reduce shipping costs. In whey applications, the whey (liquid remaining after cheese manufacture) is concentrated with reverse osmosis from 6% total solids to 10–20% total solids before ultrafiltration processing. The ultrafiltration retentate can then be used to make various whey powders, including whey protein isolate. Additionally, the ultrafiltration permeate, which contains lactose, is concentrated by reverse osmosis from 5% total solids to 18–22% total solids to reduce crystallization and drying costs of the lactose powder.

Advantage is that you are not adding any chemicals to your water, which takes out the guess work as far as dosage. The disadvantage, if it can even be called that, is that you have to have a source of heat(fire, stove, etc.) in order to bring the water to the boiling point. Also we have to remember that this does not remove chemical such as petroleum or pesticides which can be harmful as well.