To Soften or Not to Soften?

By Hans Peterson, Saskatchewan Research Council and Ken Williamson, Alberta Agriculture, Food and Rural Development

Hard water is a very common problem in most parts of the prairies. Hard water causes scale to form in water pipes, plumbing fixtures and kitchen appliances. Scale buildup in hot water tanks and boilers increases hot water heating costs and can lead to premature failure of heating equipment. Scale deposited in clothing during washing will cause increased wear and tear on the fabrics. Soap reacts with hard water to form a curd and hard water can also cause skin flaking and irritation. In addition, more soap or detergent is needed when washing or laundering with hard water.

Dugouts that receive most of their water from spring snowmelt generally have low levels of hardness, with average levels around 100 mg/L. Dugouts that receive inputs from groundwater and wells, however, often have hard water across most parts of the prairies.

Hardness is primarily caused by the dissolved chemical compounds of calcium and magnesium. The amount of hardness is expressed in milligrams per litre (mg/L) or grains per gallon (gpg) as calcium carbonate (see table).

The level at which hardness becomes inconvenient depends upon individual preference, with scale buildup and problems with soaps and detergents becoming increasingly larger for very hard water (180 mg/L). Softening water with hardness levels between 200-1,000 mg/L will result in decreased scaling and better performance of soaps and detergents. At even higher hardness levels it becomes uneconomical to soften due to the extreme quantities of salt required.

Water softeners work on the principle of ion exchange. A synthetic resin bed (zeolite) is charged with sodium ions by regeneration with sodium chloride (salt) or potassium chloride. Hard water, containing calcium and magnesium ions, flows through the resin. Ion exchange occurs when the calcium and magnesium ions attach themselves to the resin, displacing the sodium ions. The result is soft water, free from calcium and magnesium, but with more sodium.

Usually the sodium content increases approximately 50 mg/L for every 100 mg/L of hardness removed. The amount of hardness that a water softener can remove depends primarily upon the amount of resin in the softener. One (1) cubic foot of a high capacity resin can remove 30,000 grains, or about 500,000 milligrams of hardness. This means if water is 500 mg/L hard, one cubic foot of resin will soften 1000 L of water before requiring regeneration with salt.

Today's soaps and detergents are developed for moderately hard waters (as defined above). In such water, the normal dosage of detergent provides effective cleaning. It also prevents excessive foaming and frothing, which has nothing to do with the cleaning capacity of a detergent. This capacity is determined by a combination of chemicals including surfactants. For water that exceeds the "moderately hard category", Proctor and Gamble recommends 50% more detergent be used "for every 50-70 mg/L of hardness." According to Maytag, this practise is only effective to about 240 mg/L of hardness -- they recommend softening above this amount.

Automatic dishwashing results are also affected by water hardness. Hard water will leave a white film on glassware. This film can be removed by soaking the glasses in a vinegar solution for 15 minutes. The film can also be prevented by using a rinse aid along with the correct temperature setting and amount of detergent.

Can water be too soft? Perhaps zero hardness sounds ideal, and water softening units are certainly capable of producing a finished water with zero hardness.

However, water with zero hardness is quite corrosive, and when used in dishwashers, will literally attack glass surfaces, making the glasses thinner. A hazy sheen will appear on your glasses. This sheen is called "rainbow etching" and it cannot be removed. It can be minimized by using low levels of detergents, but please follow manufacturers' suggestions of quantities to use at different hardness levels.

Before purchasing a water softener, have a thorough chemical analysis done to determine the hardness, iron, sodium, and sulphate content of your water. Determine what you would like to see in your treated water and ask a water treatment professional if it can be achieved using softening.

Water that is softened has increased sodium or potassium (depending on which salt is used) levels and may be detrimental to people on sodium restricted diets, while others may be sensitive to increased potassium levels. Consumption of softened water that is high in sulphates may increase the laxative effect and cause unpleasant taste. Softened water should not be used for drinking water.

Five-cycle, fully automatic water softeners are recommended for domestic softening. They automatically backwash and regenerate with salt, which is essential for efficient operation.

Select a meter-initiated type control valve; it will substantially reduce the amount of salt required for regeneration. The twin tank systems allow for easy cleaning of the salt tank. Water softeners can readily remove up to 3 mg/L of iron, however either a resin cleaning compound or salt with a resin cleaner added must be used. Resin cleaners prevent iron from accumulating on the resin and reducing softener performance.

Thank you to Procter and Gamble, Maytag, Lever Brothers, and The Soap and Detergent Association (USA) for their advice in preparing this article.