The Collaborative International Dictionary of English v.0.48:

Limewater \Lime"wa`ter\ (l[imac]m"w[add]`t[~e]r), n.
   Water impregnated with lime; esp., an artificial solution of
   lime for medicinal purposes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

limewater
    n 1: solution of calcium hydroxide in water used as an antacid