Source : Webster's Revised Unabridged Dictionary (1913)

Water thermometer \Wa"ter ther*mom"e*ter\ (Physics)
   A thermometer filled with water instead of mercury, for
   ascertaining the precise temperature at which water attains
   its maximum density. This is about 39[deg] Fahr., or 4[deg]
   Centigrade; and from that point down to 32[deg] Fahr., or
   0[deg] Centigrade, or the freezing point, it expands.