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Water Quality Calculator

Understanding your water quality is critical to great coffee and keeping your coffee machine in its best condition.

The Langelier Saturation Index (LSI) allows you to determine how corrosive or scale forming your water is by inputting a number of simple test results. This method takes into account the total dissolved solids (TDS); pH; general hardness (GH); alkalinity (KH) and the temperature of the water sample.

Results can range from corrosive to scale forming and the choice of water filter can then be determined to bring your water quality into a range that is both suitable for your coffee experience and which will protect your boiler and metal pipes from scale build-up. We offer a range of water filters here.

Of course, scale formation is dependent on temperature, so we look at the room temperature of water entering the coffee machine, the boiler temperature at 95 C and the steam boiler temperature of around 125 C.

Use the calculator below to determine your water quality by inputting the values and pressing “Calculate”.

Where you find that water at 95 C has an LSI reading of greater than 0.7, then scale formation is likely in the boiler and a scale reduction filter must be used to protect your boiler.

You are looking for an LSI of between 0.2 and 0.7 in your boiler at 95 C for excellent coffee and boiler protection.


TDS (ppm)
GH (Calcium ppm)
KH (Alkalinity ppm)
Temp °C


°C 23 95 125

When you have your result you can select a water fiter that will manage your water appropriately. We can do this for you too as we have not only sourced water filters with varying filtration capacity, but we also calculate the bypass needed to ensure your water falls into the zone recommended by the Specialty Coffee Association for general hardness and alkalinity (on page 13). What you want is that AFTER filtration, the general hardness and alkalinity values fall into the acceptable range at 95 C and 125 C. 

Bypass valves on the filter head are absolutely critical because you must have some calcium ions passing into your boiler or you risk corrosion and certainly flat coffee.

So after installing a water filter, setting the bypass, and making a few coffee drinks, test the water coming out of the water filter. Check that general hardness and alkalinity are within range at ambient temperature and then plug the values into the LSI calculator above, and see that your LSI falls between 0.2 and 0.9 at 95 C.

You can then be sure you have optimal water for great coffee! 


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