Most electricity we deal with every day is flowing in wires, cables, etc. However, electric charges can be collected on materials that do not conduct electricity well, such as plastic. Once that's done, these charges exert an electrical field around them.Insulators such as plastic can become "electrified" or have their surface charged up through rubbing, or rapid separation from other insulators. A simple example is to run a comb through your hair when the humidity level is low. Your hair will tend to stand away from your head as some of the electrons from molecules on the surface of the hair move over to the surface of the plastic comb. With fewer electrons, your hairs are charged up, and since they're all charged positively they repel each other, causing them to lift up.Water is a polarized material. Water molecules tend to have a small separation between their "plus" side and their "minus" side, forming what are known as dipoles (from "di" or two, and poles, referring to the plus and minus). When water is near an electrical field, these molecular dipoles change direction. If the field is due to an excess of electrons, the plus poles are pulled toward the source of the field, and the minus poles are pushed away.The force exerted by the electrical field loses strength rapidly as distance increases. If the distance is doubled, the force drops four-fold. If the distance is tripled, the force loses all but 1/9 of its strength. This behavior is known as "inverse square law" where the field strength drops off as the square of the distance.Getting back to the water, since the positive poles are closer than the negative poles to the electrons causing the field, the attraction exerted by the electrons on the positive poles is stronger than the repulsion exerted on the negative poles. The net result is that the water is drawn towards static electric fields.The following experiment is a fun way to prove the above.
