Magnetic water conditioning to prevent lime scale formation has a long and controversial history. The current interpretation of the working principle is that the magnetic field interferes with crystal nucleation and growth processes resulting in formation of less adherent forms of calcium carbonate. Here we report an observation that sheds new light on the working principle. We conducted hard water through an orthogonal magnetic field. The application of the magnetohydrodynamic force on the water caused pronounced fragmentation of the natural suspended particles. This formation of suspended nanoparticles provides solution borne nucleation centers for crystallization of calcium carbonate thus preventing limestone deposition on the macroscopic surfaces. (C) 2009 Elsevier Ltd. All rights reserved.