I have asked a bank manager once. He told me that the real inflow of money is when people lends money from the bank. The interest of the borrowed that are quite big are the ones they use to pay their employees. When somebody deposits in the bank they got their money addded with interest but at the same time this money can be an asset to the bank should they need to use it for lending.
Many circulation is how the banks make money. They have share holders that invest on them which is being used to lend money on other people and give interest from it. Though people are gaining from the savings that they put in the banks there is much higher interest the bank get when they give loans to their members.