Hard water – how tough can it be on your Washer-Disinfector?

What is hard water?

When water passes through soil and rocks it dissolves magnesium and calcium, among other minerals, and that is how so called hard water ends up in our taps. Water is considered hard when concentration of minerals exceeds 180mg per litre. That said, in the East of England tap water often exceeds 600mg – off the chart. And to make things even more complicated hardness of water may change over the course of the year!

Do you have a problem?

Easiest way is to test a sample of water. You can also simply find out whether you really have a problem looking for chalk like sports and stains hard water leaves once it dries out. If you can spot them – it is worth checking how bad it is.

What implications does it have on a Washer-Disinfector?

Untreated Hard water leaves Instruments after the cycle covered in chalk-like scales – visually their cleanliness is questionable. This, however, is the least of our worries, as this deposit is made from water that was used in disinfection stage only – in principle – it should be protein free.

However, what we have not yet considered, is the fact that our process chemicals react with minerals dissolved in water. This means that a part of our “chemical cleaning force” gets absorbed by water itself. Popular water softeners work on the principle of Ion Exchange – a process where calcium and magnesium get exchanged for sodium or potassium. Now think of what is the basic ingredient of your alkaline detergent… Yes you are right, it is one or the other.

In case of enzymatic detergents the chemistry involved is more complex. Different enzymes are responsible for breaking down proteins, fats and lipids and the formulae from different manufacturers will differ significantly. One thing is certain, irrespective of the formula, detergents will react with minerals dissolved in water as well.


The hard truth is that hard water will increase costs. You can tackle the problem by installing an Ion Exchange water softener. It will resolve the problem of scaling but what needs to be taken into the account is the fact that this chemical process “exchanges” Ions but does not remove them.

The ideal solution would be to use Reverse Osmosis (RO) water, as this process involves pushing water through semi permeable membrane, which removes minerals. The problem is the cost versus the efficiency of the plant – which is high, to say the least. In some cases Washer-Disinfectors use RO water for the final rinse but this will only partially resolve the problem..

Third solution is the chemistry. The primary concern is the efficacy of the wash itself, therefore the amount of chemical used should be adapted to compensate for water hardness. Secondly, a rinse aid of some sort should be added to the disinfection stage to remove scaling. Rinse aid through lowering surface tension will also speed up drying and for these two reasons it is highly recommended.


You cannot ignore or escape from the hard water problem – not unless you relocate – so the most sensible option is to compare the cost of each solution in your particular case. It is important to do it over a longer period of time and find out what makes more sense. To go outside of the box, think whether you could use softened water for more than just your Washer-Disinfector. RO water could be used in Autoclaves, while Ion Exchange system could provide softened water in all your taps.

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About the author

Pawel de Sternberg Stojalowski

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Pawel de Sternberg Stojalowski MBA, MSc, BSc is a research and development specialist focusing on innovation within decontamination sciences. He’s been involved in R&D since 2007, designing equipment, processes and methodologies for cleaning, disinfection and sterilisation of surgical instruments as well as medical and laboratory equipment.