Calcium Build-Up in Kettles and Domestic Pipes
Puzzle 5 of New Year's Resolutions Easy Pack
Question is: Calcium Build-Up in Kettles and Domestic Pipes
and the answer is: LIMESCALE
Word Meaning:
LIMESCALE — A white, chalky deposit of calcium carbonate found in kettles, washing machines etc., especially in a hard water area.
Definitions from Wiktionary.