The Water Course

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Make Predictions — Protect Your Equipment

TWC 3.01.1 – An App to Calculate Your Water’s LSI

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LSI Calculator
Bottle Calculator
0 °C:
95 °C:
125 °C:
ppm    (mg/L)
ppm    (mg/L)
ppm    (mg/L)


Using the App

There are three separate calculators built into the app: to switch between them, click on the title at the top. Once you’ve selected the calculator you want to use, enter your measurements on each line, and click ‘calculate’. The results are displayed at the bottom.



Where relevant, you can choose different units with the drop-down menus on the right. If you are using a drop test kit to measure your GH and KH, one drop is normally equivalent to one degree of hardness (°dH). Otherwise, hardness measurements in ppm refer to CaCO3 equivalents.


LSI Calculator

This makes calculating your LSI as simple as possible. Check your water’s TDS, pH, hardness (GH), and alkalinity (KH), and enter the values in the app. You can also optionally enter a temperature.

The app assumes that all the GH in your water is due to calcium. For most people, the GH is nearly all calcium, so this is a reasonable approximation. If you do know the calcium and magnesium concentration of your water, then you should enter the GH reading from calcium alone for a more accurate result. If your water treatment includes a magnesium mineralisation step, then it’s essential to measure the calcium concentration separately.

NB: If you are making your own water with magnesium salts (such as epsom salts) then the LSI calculation does not apply as no calcium is present. We do not recommend using this kind of water in espresso machines.

The app will calculate the LSI of your water at three temperatures: 95 °C (the temperature of a brew boiler); 125 °C (the temperature of a steam boiler); and the temperature you chose.

An LSI above 0 indicates that scale is likely to form, while an LSI below 0 indicates corrosion is more likely. A thin layer of limescale is helpful to protect a machine against corrosion, so we recommend adjusting your water treatment to achieve an LSI between 0.2 and 0.7.