Finding the best water treatment for a home is no simple matter. The first impulse is to buy the cheapest water treatment system available, but this might be a mistake. Water problems can be caused by several factors, each needing a specific kind of treatment. To get the wrong one is a bother and a waste of money, so the selection should be done with care.

The first step in addressing any home water problem is to determine what it is. Perhaps the homeowner has detected a nasty smell and color in their water, or maybe there's a ring around their plumbing fixtures. The best water treatment can only be determined by analysis of the water. In some cases this can be done by an office of the municipal or county government, while in other cases it will be necessary to use a testing lab.

This analysis should pinpoint the cause of the problem. In all likelihood, it will be one of several possibilities:

• Hard water: One common problem is hard water. This occurs when the soil contains high levels of magnesium and calcium ions which dissolve in the groundwater. Results including mineral buildup, bathtub rings, poor foaming of soaps and detergents, premature fading of textiles and skin irritation after bathing.

These minerals can build up inside pipes and water heaters, restricting water flow and eventually causing expensive damage. When this buildup gets thick inside a water heater the heating element must work harder, resulting in unnecessarily high power bills.

The best water treatment for this difficulty is a softener. Here water passes through a filter made of ion-exchange resin treated with sodium ions. As this happens, the calcium and magnesium ions in the water are exchanged for sodium ions in the filter. Sodium does not cause the problems associated with hard water, so the water is said to have become softened. Eventually the filter will become saturated with magnesium and calcium, causing a loss of filtering ability. When this happens the filter is backwashed to remove magnesium and calcium, after which salt is applied to replenish the sodium ions.

• Particulate matter: A common problem, especially in households using well water, is suspended particulate matter.

The most effective water treatment for this problem is a fiber filter in which water is forced through a filter of rayon or cellulose. If color and smell persist it may be necessary to use multiple filters. Fiber filters are often effective at removing fuel products, pesticides and other organics. They are also the cheapest water treatment system available.

• Iron: In some areas dissolved iron results in rust buildup on plumbing fixtures. A softener system is sometimes the best water treatment for this, though high iron levels may require chlorination, a special iron filter or both.

• Ph: Another issue with some homes' water is the Ph level. Ph is a measure of acidity and alkalinity, and it should be around 7. If it is too low or high it can cause corrosion, making metals dissolve and build up inside pipes. The best water treatment for this is either a neutralizing filter or a chemical feed pump.

A neutralizing filter can treat water with a Ph as low as 6. Buyers should be aware that some of these filters use magnesium oxide as a filtering medium, and will make the water harder.

A chemical feed pump is used for water with a Ph less than 6. This device pumps sodium carbonate, sodium hydroxide or potassium into the water. Sodium carbonate and sodium hydroxide are the cheapest water treatment in this case, but will raise the sodium content of the water. Potassium does not do this, but costs more makes the water harder. If the Ph is higher than 7, diluted sulfuric acid is used in the chemical feed.

Be careful! Sulfuric acid is extremely dangerous, and the owner should never try to add acid to the system. When more acid is needed, a professional water maintenance service should be called.

• Other metals and minerals: This category includes harmful substances like arsenic, mercury and lead as well as minerals like nitrate and sulfate. These are the most dangerous contaminants in household water, some of which are known to cause mental retardation, birth defects and other extremely severe effects. The best water treatment for this category is either a reverse osmosis unit or a distiller.

A reverse osmosis system will have a pre-filter to remove particulate matter, a filter of activated carbon and a membrane for further filtration. This membrane must be replaced periodically as instructed by the manufacturer. This is a large unit including a holding tank for the filtered water, which may cause space problems. It's not the cheapest water treatment system, with units typically ranging from $600 to $900, but in some areas units can be rented.

A distiller evaporates water and re-condenses it, removing virtually all contaminants. Here again, a possible obstacle is the size of the unit, which must include both a boiling tank and a storage container. Unlike other systems that are driven entirely by water pressure, this one must use electricity to heat the water to boiling.

• Bacterial growth: While some newer systems use ultraviolet light or ozone to kill bacteria, the most common method is chlorination. A professional water service will first "shock" the water by adding a large amount of chlorine to kill the existing populace of bacteria. This may be done more than once. When the desired result is achieved, a continuous chlorination system is installed to keep a low level of chlorine in the water and discourage future bacterial growth.

With this information and the results of a water sample analysis, the homeowner can make an intelligent choice of water treatment system. One should always keep in mind that some systems have higher operating and maintenance costs than others, so the one with the lowest price tag may not be the cheapest water treatment system in the long run. Professional services who install these systems will be glad to advise shoppers about the best water treatment unit for their home.