FAQ: After mixing a solution of limewater is the sediment left in the bottom of the container reusable till it is completely dissolved or should it be discarded ?

It is very likely that the excess calcium hydroxide (kalkwasser or lime water) that has settled to the bottom will not dissolve and will have to be discarded. The longer it sits, the more likely the hydroxide will convert the CO2 in the water to carbonate. This carbonate will form a precipitate with the calcium (calcium carbonate) and will not dissolve.