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

The Water Calculator

Everything you need for perfect water, in one app

This tool helps you to design the perfect water for your coffee. Whether you’re checking that your RO water is safe to use in your espresso machine, or designing your own custom water for filter brewing, the app can simplify the calculations you need to make, so that you can spend more time brewing.

There are three parts to the app:

  • LSI Calculator (langelier saturation index). This tells you if your water is liable to cause limescale or corrosion inside your espresso machine.
  • Remineraliser. If you’re mixing up your own water recipes, this tells you how to get to the water you want. Armed with this calculator, you can use mineral water as a base to make your own custom water, instead of buying distilled water.
  • Bottle calculator. Not sure if your favourite brand of mineral water is good for brewing? This calculator translates the mineral composition into GH and KH for you.

For more information about how each calculator works, read the detailed instructions at the bottom of the page.

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.

You can read more about the LSI and how it works in The Water Course, only available with a Barista Hustle Unlimited subscription.


This calculator helps you design your own custom water, using the concentrate recipes found in our Water Recipes blog post, and extends it to work with any kind of water.

You need to make your concentrate solutions with the same water you intend to mineralise — so if you want to experiment with remineralising Spa water for example, then you should also use Spa water to make the concentrates.

Your concentrate recipes are as follows:

  • Hardness: 2.45 g of Epsom salts in 1L of water
  • Buffer: 1.68 g of sodium bicarbonate in 1L of water

Then we can use those concentrates to create the water that you want. First, enter the GH and and KH of your starting water. You can pick from common brands of soft mineral water in the dropdown on the right, or enter your own measurements.

Next, enter the GH and KH of the water that you want to produce. You can pick some of the standard BH recipes in the dropdown on the right, or choose your own target GH and KH.

Finally, choose an amount, in either litres or gallons, and click ‘calculate’.

Bottle calculator

If you don’t know the GH and KH of your favourite mineral water, you can save yourself the trouble of measuring it and use this handy calculator instead. Look on the label for the ‘mineral analysis’ or ‘nutrition information’. This lists the amount of various minerals in the water, in milligrams per litre.

The numbers that we’re interested in are Calcium, Magnesium, and Bicarbonate. Enter these in the app and it will calculate the GH and KH of this water for you.