It is very easy to magnetise water once it has come from the tap. You simply place magnets of a sufficient type and strength in the water, these tend to be Neodymium magnets and they have to be coated in a non corrosive type substance to actually stop them from rusting. The easiest way is to use what is called a water wand or a coaster which is placed into the water or you place the water on a coaster. The difference between using a wand to a coaster is, when you place the wand into the water the magnetism is taken quicker because the wand is placed directly into the water. If you place your glass or cup or your bowl or jug of water on to a magnetic coaster it takes a lot longer for the magnetism to go through because it has to penetrate through the vessel