Membrane pore sizes can vary from 0.1 to 5,000 nm depending on filter type. Particle filtration removes particles of 1 µm or larger. Microfiltration removes particles of 50 nm or larger. Ultrafiltration removes particles of roughly 3 nm or larger. Nanofiltration removes particles of 1 nm or larger. Reverse osmosis is in the final category of membrane filtration, hyperfiltration, and removes particles larger than 0.1 nm.[11]
If you are looking for the best ways of treating your water, Schultz Soft Water is your best source of advice on best water purification methods and custom solutions to your water purification needs. Reverse osmosis is the best option, whereas filtering is good for basic water tasks such as sediment and chlorine removal. Reverse osmosis covers a larger spectrum of contaminant removal.

Bromine and iodine can also be used as disinfectants. However, chlorine in water is over three times more effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and over six times more effective than an equivalent concentration of iodine.[16] Iodine is commonly used for portable water purification, and bromine is common as a swimming pool disinfectant.
Bromine and iodine can also be used as disinfectants. However, chlorine in water is over three times more effective as a disinfectant against Escherichia coli than an equivalent concentration of bromine, and over six times more effective than an equivalent concentration of iodine.[16] Iodine is commonly used for portable water purification, and bromine is common as a swimming pool disinfectant.
Formally, reverse osmosis is the process of forcing a solvent from a region of high solute concentration through a semipermeable membrane to a region of low-solute concentration by applying a pressure in excess of the osmotic pressure. The largest and most important application of reverse osmosis is the separation of pure water from seawater and brackish waters; seawater or brackish water is pressurized against one surface of the membrane, causing transport of salt-depleted water across the membrane and emergence of potable drinking water from the low-pressure side.
Portable reverse osmosis water processors are sold for personal water purification in various locations. To work effectively, the water feeding to these units should be under some pressure (280 kPa (40 psi) or greater is the norm).[9] Portable reverse osmosis water processors can be used by people who live in rural areas without clean water, far away from the city's water pipes. Rural people filter river or ocean water themselves, as the device is easy to use (saline water may need special membranes). Some travelers on long boating, fishing, or island camping trips, or in countries where the local water supply is polluted or substandard, use reverse osmosis water processors coupled with one or more ultraviolet sterilizers.
Drinking water sources are subject to contamination and require appropriate treatment to remove disease-causing agents. Public drinking water systems use various methods of water treatment to provide safe drinking water for their communities. Today, the most common steps in water treatment used by community water systems (mainly surface water treatment) include:

Gas hydrate crystals centrifuge method. If carbon dioxide or other low molecular weight gas is mixed with contaminated water at high pressure and low temperature, gas hydrate crystals will form exothermically. Separation of the crystalline hydrate may be performed by centrifuge or sedimentation and decanting. Water can be released from the hydrate crystals by heating[25]

In a reverse osmosis filter system, your regular water pressure pushes the water through a membrane and additional filters to remove impurities, which are then flushed down the drain. It’s a rigorous filtering process, a GE Reverse Osmosis System filters water three times, for example. Membranes and filters need to be replaced every six months to two years depending on the type of filter and how much water you use.
We were looking for to replace an RO unit that was many years old and were impressed with iSpring's RO / UV / Ph / multi-filter options, with the More-Is-Better paradigm. Patience is required for the multipart installation because the directions are vague. We also had to run a GFCI receptacle for the UV. The UV does warm the water a bit but we remedied this by running an additional line to the fridge for cold water and ice. The system was flushed a half dozen time over two days. The initial glass was cloudy but that cleared to show some carbon from that particular filter. The water taste great and we highly recommend this drinking water system.
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.

While nearly everyone loves the taste from this water filtration system, a few people tested the pH and complained that it wasn’t as alkaline as they hoped for in a system that adds back beneficial minerals. However, the company points out that the pH filter will raise acidity by 1-1.5 levels, so the final pH will depend on the chemistry of the water that you’re starting with. 

According to a 2007 World Health Organization (WHO) report, 1.1 billion people lack access to an improved drinking water supply; 88% of the 4 billion annual cases of diarrheal disease are attributed to unsafe water and inadequate sanitation and hygiene, while 1.8 million people die from diarrheal disease each year. The WHO estimates that 94% of these diarrheal disease cases are preventable through modifications to the environment, including access to safe water.[1] Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and for storing it in safe containers could save a huge number of lives each year.[2] Reducing deaths from waterborne diseases is a major public health goal in developing countries.
We all know that dehydration can be dangerous, leading to dizziness, seizures, and death, but drinking too much water can be just as bad. In 2002, 28-year-old runner Cynthia Lucero collapsed midway through the Boston Marathon. Rushed to a hospital, she fell into a coma and died. In the aftermath it emerged that she had drunk large amounts along the run. The excess liquid in her system induced a syndrome called exercise-associated hyponatremia (EAH), in which an imbalance in the body's sodium levels creates a dangerous swelling of the brain.
Many books and articles suggest this method as a safe alternative when lacking water filtration or purification methods. Without testing equipment some methods are difficult to prove. Norseman of Survivology 101 posted two great blogs which include testing done while he trained with the Norwegian school of Winter Warfare. The testing shows that the Mash or Seep showed zero improvement in lowering the bacterial count. Norseman is a retired Marine who held a Scout Sniper Survival instructor position at the First Marine Division, and SERE instructor.
Use a commercial water filter. A commercial water filter is the easiest and most effective way to filter sediment, pathogens, metals, and other pollutants from water. These filters contain special materials like charcoal, carbon, ceramic, sand, and cloth that are specially designed to filter out dangerous pollutants.[7] There are many different types of filters you can use, including:

A reverse osmosis system is typically installed under the sink, but you can install it where your water enters the house, so all your water is filtered for contaminants. RO filter cartridges provide the most effective filtration of any water purifiers. The membrane and filters remove up to 99 percent of contaminants such as arsenic, lead, ammonia and chlorine, as well as toxic fluoride, sodium, nitrates and heavy metals. The 6 stage RO filters provide a deep filtering process, leaving you reverse osmosis water, free of sediments and toxins. RO water is perfect for drinking, cooking and making ice.