Household Water Purification Methods

Households use a variety of methods to purify their water. This includes filtration, chlorine and distillation.

Water filters remove chemical and biological contaminants. They can reduce the concentration of nitrates, bacteria, viruses and parasites. Some filters are also designed to reduce the presence of the germ Cryptosporidium, which can cause diarrhea in people with compromised immune systems.

Water Filtration

Water moves constantly through ecosystems in a process called the water cycle. As it does, it has plenty of opportunities to pick up minerals, sediment and other debris. These contaminants can affect water quality and taste, making it unfit for use in your home. Filtration addresses these issues by removing impurities in the water, giving you safe, clean drinking water.

There are a number of different types of household water filters available, from jugs to whole house systems. Some filters use multiple filtration methods to remove more contaminants. These include carbon block resins, granular activated carbon, depth filters and metallic alloys. Others use a single method, like reverse osmosis or ultrafiltration.

Some filters have a large internal surface area, packed with nooks and crannies that trap chemical impurities through a process called adsorption. They may also have a specific pore size, which can help reduce chlorine and chloramines in your tap water.

Other filters, such as those used for water distillers, work with a natural process known as osmosis. They have a semipermeable membrane with one side having a higher concentration of solutes than the other. This creates household water purification a pressure differential that allows fluid with fewer solutes to flow through to the other side, where it is collected. Water distillers are the highest-performing household water filters, delivering the purest water of all.

Chlorination

Upon addition to water, chlorine gas hydrolyses to produce hypochlorous acid and hypochlorite ions. Together these compounds are called ‘free chlorine’ and they have a high oxidation potential making them a very effective disinfectant.

When chlorine reacts with organic particles in the water, it forms chloramines (monochloramine and dichloramine at pH levels below 4.5 and trichloramine at higher pH levels). Chlorine is very effective against bacteria, but less so against viruses and protozoan cysts (e.g. Giardia and Cryptosporidia). Free chlorine levels of up to 4 milligrams per liter (mg/L) are safe in drinking water, although many people would find this unpleasant.

Chlorination does not need to be done at a specific time point in the process of water treatment, and can be added as soon as the initial filtering and sedimentation stages are complete. However, the longer that chlorine has contact with microorganisms in the water, the more effectively it will disinfect them.

Chlorination is not the only way of disinfecting water, but it is a cost-effective method that can be used to treat water from unknown sources. This is especially important in rural and poor areas where visual inspection of water can often not be relied on for determining whether it is suitable for human consumption. Water should always be tested using chemical and microbiological methods before deciding on the appropriate water treatment method.

Disinfection

Disinfection involves the addition of a chemical to water that reacts with or destroys disease-causing microorganisms. The disinfectant may be chloride or its derivatives, oxidizing agents (such as potassium permanganate or iodine), or ultraviolet radiation (UV) or light (Ozone).

In order to achieve microbial inactivation by a disinfectant, the concentration of the substance well water filter and softener must remain high enough for an adequate time. The nature and level of the residual needed for microbial inactivation is determined by the water source, condition and temperature; the degree of aggregation of the test microorganism; the presence of solids and particulates (which might react with or consume the disinfectant); and the propensity of the disinfectant to produce unwanted by-products.

There is a wide variation in the susceptibility of bacteria, viruses and protozoa to different disinfectants. It is therefore impractical to obtain detailed information on inactivation of specific microorganisms by disinfectants. The dosage of a chemical agent and the duration of exposure are also important for the achievement of disinfection or microbial inactivation, and must not adversely affect the aesthetic quality of the finished water.

Household-level water treatment together with safe storage and good hygiene practices can significantly reduce diarrhoeal diseases. It can help to reach the millennium development goals and is particularly suitable in places where drinking water from large centralised systems is contaminated during distribution or at household level.

Softening

A water softener removes the minerals calcium and magnesium that make hard water by replacing them with sodium ions. Water passing through a softener passes over a bed of resin beads that are saturated with sodium. The calcium and magnesium ions of household water are drawn to the resin beads and exchanged for sodium ions. The softened water then exits the system, eliminating mineral buildup and preventing soap film and spotted glassware.

The softer water produced by home softeners helps to extend the life of washing machines, dishwashers and hot water heaters. Hard water can cause these appliances to clog, which can lead to expensive repairs or early replacement. Water softeners also help to reduce cleaning products, such as detergents, soaps and shampoos, from creating soap curds, leaving behind a filmy residue in tubs, sinks and showers.

In addition, water softeners can help to improve the appearance of clothing, kitchen ware and other items that are exposed to hard water over time. Clothes that are washed with hard water can develop a dull and weathered appearance, while whites may fade in color. Water softeners also make dishes and glassware sparkle, while providing a richer clean with less effort. Regular cleaning and maintenance of a water softener is necessary, as the granules of resin can become fouled with iron or manganese fouling. This requires commercial cleaners to be used, as directed, to keep the softening process working properly.