Because magnets wear out. Magnetic perpetual machines can never work because magnets eventually wear out. This isn't the reason they don't work. Magnets can lose their magnetism in several ways; Heat them to very high temperatures. Hit them repeatedly with a hammer.
It'd never work as the first law of physics is that the law of conservation of energy. It states that energy is often preserved. To keep a machine moving, the energy applied ought to stay with the machine with none losses. As a result of this reality alone, it's not possible to make perpetual motion machines.
Water has strong hydrogen bond dipole-dipole intermolecular forces that give water a high surface tension and a high heat of vaporization and that make it a strong solvent.
