Why does slaked lime water lose alkalinity over time?
If you dissolve slaked lime in water it will absorb carbon dioxide from the atmosphere over time.
Carbon dioxide will react with hydroxide ions from the slaked lime forming mainly hydrocarbonate ions. Hydrocarbonate ions will equilibrate with water and at about pH &lt; 8 carbon dioxide will slowly be liberated from the solution. After some time, no significant amounts of hydroxide ions will be left from the slaked lime and the pH of the solution will close into neutral pH.

Well, what will happen to the calcium ions from the slaked lime? You will probably find them as an insoluble deposit at the end. This is because carbonate ions will also be formed during the process, forming calcium carbonate of very low water solubility.