Water filters remove the impurities of the water by biological process or chemical process. The filters usually clean water for various purposes including drinking water, swimming pools, irrigation and aquariums. Filters use the processes like adsorption, sieving and ion exchange for the cleaning of the water. By these processes the filters trap the contaminants, bacteria and dirt. Removing these hazardous substances will purify the water. The filters have the capability to filter substances larger than a single water molecule. So many invisible toxins are removed during filtration process.
There are different types of water filters including portable water filters, Faucet-Mount filters, refrigerator filters, shower filters, water softeners, whole house water filters, canister filters etc. Portable water filters are mainly used by the military, aid organizations during emergencies, hikers etc. These water purifiers are capable of removing dirt from all sources of waters including ponds, streams, rivers etc. These filters are light weighted, portable and small in size. So it is very easy to carry portable type of filters in the emergency kit. Faucet-Mount water filters reduce the dirt, rust and sediment content in the water. These fitters can be installed in the bathroom and kitchen faucet. The taste and smell of the water is improved a lot after installing these filters.
Shower filters are mainly user to filter the chlorine content in the water. The chlorinated water often makes the skin hard and rough. Also this type of water reduces the smoothness of the hair. Shower filters helps to prevent the skin and hair problems to a great extent by reducing the chlorine content in the water. Water softeners help to remove the harmful minerals in the water. The minerals usually leave residue on everything which in turn leads to the wear and tear of the heating and plumbing appliances. Water softeners help to remove these harmful minerals and thus save the money on cleaning supplies, clothing and energy costs.
Refrigerator filters helps to filter the ice an ice maker. Whole house water system filters the water faucets in the entire home. The contaminants and dirt in the entire water in your house is removed through this system. This system is good for removing materials like sediments and rust. Canister filters is considered as the simplest form of water purifiers. This purifier consists of a pitcher and a lid with filtration system. The water reaches the reserve tank through the filter and so the water received at the reserve tank will be pure.
The main advantage of the water filters is that they reduce the probability of getting infected to various diseases. A huge number of gastrointestinal diseases are caused by consuming impure water. Nowadays most of the water sources are contaminated. So there is great importance for the water filters in the present situation. There are a lot of visible and invisible poisonous particles in the tap water. These harmful particles cause many diseases. Recent studies reveal that some types of cancers are caused by the hazardous particle present in the drinking water. Water purifiers make the water safe to drink by removing the contaminants in it.
I have a Sweetwater Guardian, and I like it. It’s probably easier to pump than any other filter because of the lever it uses. I do know (from using at REI) that it pumps easier than an MSR filter with a similar lever. However, if I were buying a filter for the first time, I would consider an MSR Miniworks or Waterworks or a Katadyn Pocket Filter or Minifilter. The MSR filters attach directly to a water bottle (or my MSR Dromedary water bag), so there’s no output hose to get contaminated. The Katadyn filters seem to get the most use out of their replaceable filter elements, if their claims as to filter life are accurate. All of those filters have the requisite pore size (.2 microns, I believe) to filter out cysts, protozoa, and most bacteria. In any case, check out the monthly panel here about water filters and contaminants, or go to rei.com and find their chart that compares the abilities of various makes and models of filters, to make sure the one you buy removes the things from the water that you want it to. And remember this is only one opinion (mine) among many. You may place greater emphasis on other factors in choosing a water filter. A trick to extend the life of any water filter, which I probably read in this newsgroup, is to cover the “prefilter” at the end of the intake hose that goes into the water source with a coffee filter, to strain out the larger contaminants and keep them from clogging the filter element. 
After living with intestinal distress for a long time, and driving ourselves insane trying to figure out what could have been causing it, we have finally fixed on tap water as the most likely cause. (We’ve known for a long time that the water here was hard — stains on the toilet attest to that! — and it may be that, or it may be something else.)
I’m off to Nepal to do some trekking soon and considering taking a water purifier with me mainly to ensure a safe supply of drinking water but also to do my bit at reducing the plastic bottle pollution epidemic. Can anyone recommend a good purifier that’s both compact and capable of producing enough clean water for two people for the duration of the Annapurna Circuit trek I’m reckoning on about a liter each a day for twenty one days. All I can say is, make sure you have some iodine tablets (and something to kill the taste) because you never know when the darn machine’s going to break.
We have a Pur water purifier which needs a replacement filter every so often. When we recently went to our local camping store, where the purifier was bought, to buy a new filter, we were told they are no longer allowed to sell these. There are plenty of stocks we were told, but they are not allowed to sell them, or the purifiers. However they cannot or will not say why, or whether this is a permanent or temporary state of affairs. They also refused to tell us how or where to contact the makers of the product! They say a similar ban applies to the Sweetwater brand purifier. Does anyone know anything about why the purifier & filter are banned, &/or where to contact the manufacturer, or any other relevant information?
A water purifier is very different from a water filter. Figure out what you need. A purifier may be a desalinizer, such as a reverse osmosis membrane that removes salt from sea water. these will be more expensize to buy and keep up (replace membrane cartridges).
