As far as I can tell the only effect is an electrostatic one. You can see how a charged rod held next to a fine stream water will deflect the stream. There's a video of it on YouTube. This is a common classroom demonstration and you can find it explained all over the web in lots of places. There's also something called Lord Kelvin's water dropper which uses dropping water to create a charge difference that can make a spark or light some bulbs. You can learn more at Wikipedia. On the microscopic scale in so-called nanotech devices these electrostatic properties of water are used in tiny pumps and other mechanisms. Water begins having very strange properties at very small scales due to it's polar nature and also from a phenomenon called hydrogen bonding--the weak bonding force responsible for water tension. A google search on nanofluidics will provide more information.
If you are asking this question because you are thinking of investing in a magnetic or electrical device to treat water, beware of con artists. You will find TONS of stuff out there about magnets affecting or fixing the flow of water in pipes, or purifying water, or making water healthier or imbuing it with some kind of power, but this is pseudoscience, or snakeoil. There are no respected papers published on these phenomena in accredited physics or chemistry journals. A good review of all this "junk science" can be found at H2O dot con.
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