If we look closely around our surroundings, we see everything as objects. Each and every object are made up of many composition composed of sub compositions. However, if we go to deeper compositions, we would realize these objects are made of atoms.
Each and every atom carry a charge called proton and electron. Protons are positive charges and electrons are negative charges. The state of an atom is called neutral if the number of protons is equal to the number of electrons. These charges by law of physics attract each other.
When two objects collide (like rubbing each other), the atoms of these objects clashes and their charges mixes up. Depending on the material, like rubber, some attracts more charge than the other. Thus, if we look at the video above, the rubber balloon became negatively charged because it took a lot of electrons from the hair. On the other hand, the hair became positively charged because most of its electrons are transferred to the rubber thus leaving mostly protons. Since electrons and protons attract, the hair remained sticking to the rubber balloon as an effect. The flowing water from the faucet is also made of atoms that is in neutral state. However, when the negatively charged balloon got close to the water, it attempted to attract the positive charges from the water making it bend.