The pH of saturated limewater is 12.54 at 25 deg C. At lower temperature, but still saturated, the pH is higher. pH is not an especially good way to monitor limewater saturation because it only drops about 0.3 pH units when the concentration drops by a factor of 2. But it is qualitatively useful to compare the pH side by side of a saturated limewater standard (say, 2 teaspoons in a cup of water) to whatever you want to measure.
Conductivity is a better way to measure limewater potency, and I show how to use it in this article:
The Degradation of Limewater (Kalkwasser) in Air
http://reefkeeping.com/issues/2003-0...ture/index.htm