I have a hot water dispenser, which heats the water to the temp you specify, on-the-fly. Sometimes this technology is called “insti-heat”. Instead of filling a kettle and waiting, it pumps water from a tank and heats it inline as fast as it draws it. Likely similar to how Nespresso machines work.
This means the limescale is hidden in the internal tubes. When descaling solution is put in the tank and the descaling program runs, there are no white chips of limescale like you would get in a water kettle. Yet it seems to be working because after descaling the water flows smoothly (as opposed to coughing and sputtering which is what happens when limescale is built up).
So it’s a mystery- where did the limescale go? Does it actually dissolve into the descaling solution? I ask because I’d rather not be wasteful.. I’d like to reuse the descaling solution, if that’s sensible.
If you have pH test strips or even a pH-meter you can check it yourself. Dissolving the lime scale will change the pH of the solution. So just check the ingoing and outgoing solution.