Abstract: Apparatus and method for removing hardening calcium-containing and similar minerals from water, in which raw water is passed through a passage, having a reduced cross-sectional area, in an elongated core of a suitable alloy. The passage is provided with closely-spaced parallel walls which have been polished to an image reflective smoothness and etched to create a multiplicity of randomly-positioned microscopic channels and a multiplicity of complementary mesas having smooth, flat tops. The reduced cross-sectional area causes a pressure drop in accordance with Bernoulli's Principle, which causes carbon dioxide to come out of solution, the presence of which inhibits precipitation of calcium carbonate and forms carbonic acid to attack existing scale. The small size and shape of the mesas allow calcite crystals to begin to grow but permit them to break off after a certain size has been attained. The freed calcite crystals then provide nuclei for crystals to grow from the supersaturated solution.