Water Softener Function

This article is a guide to the use and function of water softeners in commercial catering appliances - particularly regarding dishwashers, glasswashers and washing machines. This is nothing to do with the purification or filtering of drinking water; or indeed the use of artificially softened water for drinking purposes. We are dealing here with the softening of mains water for the washing and cleaning of kitchen utensils, glassware and laundry.


Hard Water

Around 60% of UK households and businesses are in hard water areas. We often hear the terms hard water and soft water, but what exactly is meant, and is one “better” than the other?

Hard water contains many more minerals in its make-up; specifically calcium and magnesium, mainly in carbonate form. This, on the face of it, sounds like a good thing: minerals are good for us, aren’t they? In fact hard water as a drink is far more beneficial.

Soft water, on the other hand, has much less mineral content. There is of course lots of middle ground where water could be described as “slightly soft” or “moderately hard” etc.

The problem with these calcium and magnesium salts in water for washing and cleaning (and for boiling in kettles and water boilers) is that they have several disadvantages.

The first is that hard water is incapable of producing an effective lather when mixed with a soap or detergent. Whatever it is you’re cleaning – dishes, glasses or clothes - doesn’t get thoroughly clean; and even if it does, it takes much longer. And because you have to use very large amounts of soap, it becomes an expensive operation as well. The minerals in the water react with the detergent to form a solid precipitate, a soap scum, rather than a lather. This precipitate is responsible for the stains and discolouration sometimes seen on cutlery.

Second, these minerals form deposits, usually called limescale, that clog pipes, tanks and plumbing. These are deposited as off-white solids on the internal surfaces of pipes and will eventually block, for example, the rotary jets of a dishwasher.

Thirdly, galvanic corrosion of metals can occur when different metals are continually immersed in hard water. Regular and on-going use of hard water will greatly shorten the working life of the appliance. This is expensive. 

So, the first thing to work out is the level of water hardness in your part of the country. This can be discovered quite easily by visiting the web site of your water supplier, where levels of calcium and magnesium are given, usually under the heading water quality.

Also, water testing kits are readily available from DIY stores and online retailers for a more precise reading at your premises. Water hardness is normally expressed in parts per million (ppm). The average reading in this country is surprisingly high at 286ppm.

There is no requirement for a water softener in levels of less than 100ppm; although it may still be a good idea because even low levels of minerals will eventually cause failure of the appliance. And at the very least, a water softener will lessen the need to dismantle equipment frequently to deep clean rotary jets. At levels of 100 – 300ppm a water softener is strongly recommended. Water with a reading of over 300ppm requires a high-spec softener.


Water Softener Function 

So, let’s have a look at how water softeners work.

Water softeners’ active constituent is an ion exchange resin in the form of polystyrene beads. These beads attract and bind the calcium and magnesium ions in the hard water and exchange them for sodium. After a time, and depending on the frequency of use of the machine and the hardness of the water, the beads become full of the calcium and magnesium and the resin needs to be cleared of them, or “regenerated”, to become functional once again.

This involves flushing with brine, a solution of salt, or sodium hydroxide, which is then flushed away. It’s basically a chemical transfer.


Selecting a Water Softener

Some models of dishwashers and glasswashers have integral water softeners; so there is no need to make a separate purchase. As we outlined above, the ion exchange resin in the water softener needs to be “regenerated” at regular intervals through the addition of salt or salt water. With integral water softeners this happens automatically, which is a great labour-saving benefit as well as bestowing peace of mind.

What does need to be borne in mind though is that water softeners don’t function as well in water temperatures greater than 30°C. This may affect the decision on a hot fill or a cold fill warewasher. There are machines on the market today, however, which allow temperatures up to an absolute maximum of 60°C.

The other decision to be made is the type and size of warewasher most suitable for your business: a front loading machine or a pass-through washer. That, of course, is a subject in itself but here we are concentrating on the use of water softeners.

In terms of water softener activity, the DC range of warewashers will complete, at 300ppm hard water, 40 wash cycles (or 125 litres) for front loading machines and 80 wash cycles (or 250 litres) for pass through machines before the water softener must be regenerated.

Turning briefly to washing machines, we see similar problems in hard water areas. Limescale build-up on the heating element will shorten its life. The scale acts as insulation and the element gets hotter than is intended, leading to eventual failure or break down; a side-effect of this obviously is a greater consumption of electricity. Similarly, limescale residue on internal surfaces, including hoses and seals, will accelerate their disintegration.

Again, more detergent is required in hard water areas to wash clothes properly, and hard water itself can damage the fibres in clothing.

The good news is that most manufacturers of washing machines state, unequivocally, that the problems above will be avoided if a good quality detergent is used and, equally importantly, at the correct dosage. If the correct dosage is not used then the ingredients of the detergent which are designed to soften the water will not work.